L'-RARY
UNIVERSITY OF
CALIFORNIA
DICHROISM AND SPECTRA OF PRECIOUS STONES
SAPPHIRE
RUBY
EMERALD
PERIDOT
BROWN TOURMALINE
BROWN TOURMALINE
ANDALUSITE
ALEXANDRITE
ALMANDINE GARNET
a B C D
E b
ZIRCON
a B c D
BOARD OF EDUCATION, SOUTH KENSINGTON,
VICTORIA AND ALBERT MUSEUM.
PRECIOUS STONES
CONSIDERED IN THEIR SCIENTIFIC AND
ARTISTIC RELATIONS
WITH A CATALOGUE OF THE TOWNSHEND COLLECTION
BY
A. H. CHURCH, F.R.S..
M.A., D.Sc., F.S.A.,
Professov of Chemistry in the Royal Academy of Arts in London.
NEW EDITION.
LONDON :
PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE,
BY WYMAN & SONS, LIMITED, FETTER LANE, E.C.
1905.
Price Is. 6d. ; in Cloth, 2s. 3d.
At Museum 1/6
EARTH
SCIENCES
t'BRARY
CONTENTS.
Page
PREFACE ... v
PREFACE TO FIRST EDITION . viii
BIBLIOGRAPHICAL NOTES .
CHAPTER I.
DEFINITION OF PRECIOUS STONES . . . . . .
CHAPTER II.
PROPERTIES AND DISCRIMINATION OF PRECIOUS STONES.
CHAPTER III.
CUTTING AND FASHIONING PRECIOUS STONES . . . . . . . . 25
CHAPTER IV.
ARTISTIC EMPLOYMENT OF PRECIOUS STONES
CHAPTER V.
ARTIFICIAL FORMATION OF PRECIOUS STONES ... . .48
CHAPTER VI.
IMITATIONS OF PRECIOUS STONES . . . . . . .51
8445. 1000 Wt. 29306. 5/05. Wy. & S. 3407r a
iv PRECIOUS STONES.
CHAPTER VII.
Page
DESCRIPTIONS OF PRECIOUS STONES - . . . . . , .54
Diamond, 54 ; Corundum, Sapphire and Ruby, 61 ; Spinel, 67 ; Tur-
quoise, 70 ; Topaz, 72 ; Tourmaline, 75 ; Garnet, 78 ; Peridot, 85 ;
Beryl and Emerald, 87 ; Chrysoberyl, 90 ; Phenakite, 91 ; Euclase, 92 ;
Zircon, 92 ; Spodumene,'96 ; Hiddenite, 96 ; Kunzite, 96 ; Opal, 97 ;
Quartz, 99 ; lapis-lazuli, 102 ; lolite 103 ; Crocidolite, 104 ; Labrador-
ite, 105 ; Moonstone, 105 ; Sunstone, 106 ; Obsidian, 106 ; Epidote, 106 ;
Axinite, 107 ; Sphene, 107 ; Cossiterite, 107 ; Diopside, 108 ;
Apophyllite, 108; Andalusite, 109; Jade and Jadeite, 110; Pyrites,
111; Haematite, 112 ; Amber, 112 ; Jet, 113; Malachite, 113;
Lumachella, 114; Pearl, 114 ; Coral, 117.
THE TOWNSHEND COLLECTION OF PRECIOUS STONES . . . .119
CATALOGUE OF THE TOWNSHEND COLLECTION 122
INDEX 133
ILLUSTRATIONS.
FIGURES 1 to 11 . . . ... . . Coloured Frontispiece.
FIGURES 12 to 20 ..." . pages 26 to 30
SPECIMENS IN THE TOWNSHEND COLLECTION : pages 122 to 125
Figures 1 to 20, Plate I ... . . . facing page 122
Figures 21 to 29, Plate II .. "^ ..... 123
Figures 30 to 42, Plate III . . 124
Figures 43 to 50, Plate IV .. 12 5
PREFACE.
Since 1882, when the " Handbook of Precious Stones " was published,
the volume has been several times reprinted from stereotype plates.
Occasionally a few alterations and corrections were made in the text,
but no opportunity occurred to improve the arrangement of the work
or to add fresh material. The present issue, however, represents a
thoroughly revised edition. A large number of paragraphs have been
wholly rewritten, while so many additions have been made to the
accounts given of the different kinds of precious stones and other beauti-
ful minerals that the 112 pages of the original handbook have been
increased to 140. Among the minerals which have now received fuller
treatment may be named diamond, sapphire and ruby, and the
different varieties of garnet and of zircon. But readers who desire to
make themselves more intimately acquainted with the optical properties,
the crystal-forms and intimate structure, the modes of occurrence and
formation and the chemical composition and constitution of precious
stones, will find it necessary to turn to works in which full details of
these subjects are given. In this connection may be named the treatises
of Dana, of Professor Lewis of Cambridge, Professor Maskelyne and
Professor Miers, for in the pages of the present handbook only such
scientific considerations find place as can be easily grasped, and which,
at the same time, help to explain the beauty of precious stones and afford
methods of identifying the different kinds.
The chief localities where precious stones are found have leen named
in Chapter VII. under the headings of the several species and varieties.
But this subject cannot be adequately discussed without having recourse
vi PRECIOUS STONES.
to maps, both geographical and geological, to which no space could be
allotted in an elementary handbook. But there is one rich district
which seems to require special notice here in order to remove what seems
to be a prevalent misconception. In the body of the present handbook
frequent references are made to the occurrence of many gem-stones in
Ceylon. The search for these beautiful minerals and the traffic in them
has, in fact, been going on in that island for ages, while the plumbago and
mica industries are affairs of to-day. Yet it is strange that the im-
portance of the Ceylon trade in precious stones remains unrecognised
not only in newspaper correspondence but in official documents and
in standard looks. One meets with such a statement as this " Plum-
bago is, practically, our only mineral export" ; and this, " The yield
of gems in this island is not large, the total value of the annual pro-
duction being said to be no more than 10,000." A glance at the true
figures suffices to demonstrate the incorrectness of such statements.
The value of plumbago exported from Ceylon in 1903 amounted to
119,316. Now the value of the gems exported in an average recent
year by a single Colombo merchant was 30,000, while there are a score
of other Ceylon gem merchants who together export no less than 200,000
worth annually. With casual sales to visitors to the island and to
travelling dealers, a moderate estimate of the annual export of gems
from Ceylon will be 300,000. The variety of kinds found is large,
sapphires, spinels, alexandrites, chrysoberyls, beryls, topazes, catseyes,
tourmalines, zircons, garnets and moonstones being the chief : diamonds,
emeralds and turquoises do not occur, while pearls belong to a different
category, being organic products. But it must be allowed that the precious
stone industry constitutes now, as it has done for many centuries, an
important feature in the resources of the island.
In concluding these prefatory notes I have much pleasure in acknow-
ledging the help of Dr. C. A . MacMunn, to whose skill in spectroscopy
many scientists are largely indebted. He drew for me the absorption-
spectra of almandine and of zircon, reproduced in the coloured frontis-
piece. Although more exact in details, these drawings do not, I am glad
- . , '; PREFACE. vii
to say, present any obvious differences from the corresponding figures
in the plate issued in 1882 with the first edition of this handbook. But
they do show a marked superiority over the spectra figured in subsequent
issues. The nine upper figures in the Frontispiece show the twin
colours of certain precious stones, figs, i to 6 representing the hues as
seen in the dichroiscope.
A.H.C.
KEW GARDENS, February, 1905.
PREFACE.
(To THE FIRST EDITION).
A revised Catalogue of the Townshend Collection of Precious Stones
in the South Kensington Museum originated this Handbook, in which
an attempt has been made to associate, if not to combine, the scientific
with the artistic study of precious stones. It has been necessary to
confine this work within somewhat narrow limits, and hence to omit
much which might fairly find a place in a comprehensive treatise on
the subject. The writer, however, trusts that what is here offered for
the consideration of students and amateurs may increase the intelligent
appreciation of precious stones, and further their more judicious
treatment in jewellery. Notwithstanding the exquisite skill of a few
modern artist-workmen, it must be affirmed that there is room for
improvement in the ordinary productions of jewellers' shops, with.,
respect to knowledge, taste, and finish. Chiefly in fault, however, are
the purchasing public, who still tolerate the horseshoes, anchors, and
clumsy cables of a debased time, and are not quick to appreciate refine-
ment and originality in the selection and artistic mounting of precious
stones. So a few words about these beautiful materials their nature
variety, and employment -may prove of wider service than a mere
descriptive catalogue of the specimens belonging to the South Kensing-
ton Museum.
A. H. C.
KEW, Nov., 1882.
BIBLIOGRAPHICAL NOTES.
The following books and papers on precious stones and on related
topics may be consulted, especially for such technological,
historical, and archaeological details as do not fall within the
scope of the present work.
MDME.-DE BARRERA. " Gems and Jewels." London : Bent-
ley - - 1860
MAX BAUER. " Edelsteinkunde," pp. xvi. and 712. Leip-
zig : Tauchnitz - - 1896
MAX BAUER and L. J. SPENCER. " Precious Stones, " pp.
XVI. and 627. London : C. Griffin and Co. - - 1904
SIR G. C. M. BIRDWOOD. " Industrial Arts of India." Vol.
ii. pp. 17-32. London : Chapman and Hall - - 1881
E. BOUTAN. " Le Diamant," pp. 325. Paris : Dunod - - 1886
A. H. CHURCH. " Physical Properties of Precious Stones. "
Proc. of the Geological Association, vol. v., No. 7 - - 1878
A. H. CHURCH. " Precious and Curious Stones," " Spectator,"
July gth - - 1870
A. H. CHURCH. " Discrimination of Precious Stones. "
Journal of the Society of Arts, vol. xxix, pp. 440-446,
April 8th - 1881
L. DIEULAFAIT. " Diamants et Pierres Precieuses." Paris :
Hachette - 1871
C. DOELTER. '* Edelsteinkunde, " pp. viii and 260. Leipzig ;
Veit 1893
2 PRECIOUS STONES.
with these gems, there are doubtless several hard and beauti-
ful stones which are found in less abundance, but which remain
less costly because in less demand. Yet there is something to
be said in favour of the high position commonly given to the
diamond, the ruby, the emerald, the sapphire, and we may add
the pearl and the opal : they all possess a very conspicuous and
obvious beauty. By brilliancy and colour they force them-
selves upon our attention, while the spinel, the jargoon, and the
tourmaline generally need to be studied, to be looked into, that
their merits may be discovered. But the argument that beautiful
stones ought not to be employed in the higher kinds of bijouterie
unless they are costly is an unworthy one. It will not bear
criticism. Why should not moonstones, even if they can be
bought for a shilling apiece, be introduced into goldsmiths' work
of the most artistic sort ? Surely they may rank at least with
coloured enamels, which are of extremely small money value, but
which are prized highly when employed with skill in well -designed
jewels.
It has been before stated that the caprice of fashion influences
and alters the market value of precious stones from time to time.
The peridot, the amethyst, the cat's-eye, and the aquamarine have
each had their day, and then been abandoned for new favourites.
Even the emerald has suffered vicissitudes, and so has the opal.
The causes of such changes in the popular esteem in which particular
species of gems are held cannot often be traced. A new fashion
is set or an old one restored, and once set is blindly followed. The
introduction of a little-known gem, however beautiful it may be,
is generally a most difficult matter. A jeweller who was in the
first rank of artistic workers was showing a customer a bracelet
beautifully set with the rich green garnets of Bobrovka. This
lady admired the stones and the workmanship immensely, but
spoke of the former as emeralds. The jeweller honestly said :
" They are not emeralds, but a rare sort of garnet from the Ural
DEFINITION OF PRECIOUS STONES. 3
f
Mountains." Forthwith the lady rejoined : " Well, after all,
I do not think I care so very, very much for this bracelet ; please
show me something else." Not that she knew that there did exist
a real objection to these green garnets they are not quite hard
enough to stand much wear. For the ignorance that prevails
about precious stones, not only among the wearers and owners
of them, but also among jewellers themselves, is indeed dense.
A London goldsmith had six stones to mount as rings ; in return-
ing them finished, the invoice gave to the specimens five wrong
designations ! A few years ago how very few jewellers understood
what was wanted when a tourmaline or a jargoon was asked for !
and yet the tourmaline and the jargoon have been long known.
Diamond, ruby, emerald, sapphire, pearl, opal, turquoise ; tur-
quoise, opal, pearl, sapphire, emerald, ruby, diamond such is
the range and variety of acknowledged gems. If a novelty has to
be introduced it must be called by some modification of these
well-known names, and must become a " Cape ruby " or an
" Uralian emerald." In speaking further on, in reference to the
artistic use of precious stones, something more will be said upon
this point of the neglect of certain kinds of extremely beautiful
stones.
From the statements just made it will be gathered that although a
stone to be precious must have, in very good measure, the qualities
of beauty, durability, and rarity, yet we cannot arrange precious
stones in any fixed and definite order, by assigning them places in our
list in accordance with the degrees in which they possess these three
qualities. Even if all stones going under the same name were
equally fine this would be impossible ; much more is this the case
when we learn that two specimens say of ruby each weighing
the same, might be worth five pounds and fifty pounds respectively.
In placing these three necessary qualities of beauty, durability, and
rarity in this sequence, the intention has been to express the pre-
eminent necessity for beauty in stones deserving the name of precious ;
8445, A 2
4 PRECIOUS STONES.
the importance of durability, which must claim the second place ;
and the desirability of a certain degree of rarity, especially where the
quality of durability may not exist in the highest degree. How far
a very beautiful and hard mineral would maintain its position as a
precious stone in the event of its becoming exceedingly abundant,
one cannot venture to judge ; but as we have to deal with existing
facts only, the problem is one which practically has not yet been
presented for solution.
As precious stones have just to be looked at and worn, or used
in decorative work, it will be readily understood why no occult
property is of much moment in determining their value. Individual
and learned amateurs may indeed value a stone according to what
they know of its history, its romance, its memories-, or the curiousness
of its components ; but in ninety-nine cases in a hundred any en-
hancement of value through such causes is out of the question.
Still, from the mineral ogical and chemical points of view, it is
perhaps legitimate to import some elements of interest when ap-
praising the right of a stone to be called precious, or its place in the
list of gems. One need not follow those writers who speak of
precious, semi-precious, and common stones ; but one may reasonably
arrange the different kinds in a few groups or classes, according to
what we may call the average sum of their merits. To assign a
precise place to each species is not possible. Hence the futility of
such a classification as that published in 1860 by K. E. Kluge wherein
emerald takes lower rank than zircon, and precious opal comes after
garnet, while to turquoise is assigned a place beneath nine other
stones only one of which (peridot) is even known to dealers in
precious stones, and to the purchasers of jewels.
CHAPTER II.
PROPERTIES AND DISCRIMINATION OF PRECIOUS STONES.
SUCH properties of precious stones as are perceptible to the eye
unaided by optical apparatus, but trained to keenness of vision,
afford valuable means of discriminating precious stones from one
another, but do not exhaust such means. Indeed, such mechanical
properties as hardness and specific gravity are of the greatest
use in determining the species of a stone, and are more commonly
available than the majority of optical tests. Optical properties
must, however, ever hold a chief place in all artistic classifications
of precious stones, so that it will not be unadvisable to begin the
present chapter by a synopsis of the most obvious characters of
this class. They may be arranged in the form of a tabular view,
the use of which is twofold, enabling us to define the several optical
properties found in gem-stones, and also to appreciate their artistic
capabilities. We arrange these optical (or mainly optical) qualities
under the general heads of " Surface " and " Substance : "
/ 1. Plane.
SURFACE.
Form.
Lustre.
2. Curved.
3. Metallic.
4. Adamantine.
5. Resinous.
6. Vitreous.
7. Waxy.
8. Pearly.
9. Silky.
SUBSTANCE.
PRECIOUS STONES.
10. Transparent,
11. Translucent.
Light. ^ 12. Opalescent.
Chatoyant.
Opaque.
Iridescent.
16. Monochroic.
\ 17. Pleochroic.
[ 18. Fluorescent.
The greater number of these terms will be found illustrated in
the present and succeeding chapters : we now proceed to the
discussion of the qualities which underlie them, and of other im-
portant physical characters of precious stones. The order which
will be followed may be gathered from this scheme :
REFRACTION.
DISPERSION.
POLARIZATION.
PLEOCHROISM.
HARDNESS.
SPECIFIC GRAVITY.
FORM.
STRUCTURE.
Refraction of Light. The familiar experiment of plunging a
stick in a vessel of water and observing the broken appearance
which it assumes, serves to illustrate the action called " refrac-
tion," or bending back. This refraction of light occurs in the
majority of cases where a ray of light falls upon one transparent
medium from another say from the air upon a diamond. Part
of the incident light enters the diamond, and follows a different
path is refracted. The diamond, like liquids, glass, and other
molten or vitreous that is non-crystalline matter, possesses the
property of simple refraction ; many precious stones, indeed the
REFRACTION OF LIGHT. 7
majority, are doubly refractive. A bright spot of light, say a
small candle-flame, when viewed through a single refracting stone
appears single ; through a doubly refracting stone, double. The
stone should be moved from the eye until, even when at a con-
siderable distance, the flame seen through it appears single or
double, as the case may be. All crystals belonging to the cubical
system, such as diamond, spinel, and garnet, are, like glass and
strass, simply refracting ; ruby, beryl, topaz, and quartz are all
doubly refracting. There are very precise and beautiful methods
for ascertaining this quality in transparent crystals, but they are
not applicable generally to cut and polished gem-stones. The
results of some of these accurate measurements of the indices of
refraction of transparent minerals will be found in chapter vii. ;
that they differ much in different species .may be seen from this
brief list of indices for the yellow ray :
Diamond . . . 2-417
Zircon .... 1 '950
Almandine . . . T810
Ruby . . . .. 1-779
Pyrope . . . T750
Chrysoberyl . . 1'748
Peridot . 1-659
Tourmaline ... 1 -642
Heavy flint glass . 1 -619
Beryl . . . . 1'575
Rock crystal . . 1 -549
lolite . . . . 1-540
Crown glass . .1 '524
Water 1-336
Although this series of refractive indices may be accepted as
containing numbers near the truth it must be remarked that
every doubly refracting substance has two indices of refraction
for each ray, although the difference between these indices rarely,
if ever, exceeds five units in the second decimal place, and generally
amounts to no more than one unit. And it should be mentioned
that the same species of stone, even in its apparently purest con-
dition, does not present, in all specimens, precisely the same optical
features ; there are differences due in part to chemical, in part
to molecular causes. Thus there have been observed in fine
diamonds variations of refractive index amounting to several units
8 PRECIOUS STONES.
in the second decimal place, while in the case of zircon specimens
of the different varieties have furnished, for the ordinary refractive
index with yellow light, figures ranging between 1-95 and 1*84,
that is a difference of 0*11. The unit to which all these indices
are referred is that of air, which is taken as i ' o. In connection with
the refraction of light by precious stones mention should be made
of the phenomenon of total internal reflection. This, so con-
spicuous in the case of diamond and other gems of high refrangibility,
fills the stone with light and contributes very largely to the beauty
of its appearance. This subject is fully discussed in Part I. of
the volume on Precious Stones by Dr. Max Bauer and Mr. L. J.
Spencer.
Dispersion of Light. When a ray of light passing from one
medium to another is bent or refracted, the light being composite
and consisting of rays having different degrees of refrangibility, it
suffers dispersion as well as refraction. In this way the several
component rays, differently coloured, are separated more or less
widely from each other, .and are said to be dispersed. Upon this
property of gems depends that peculiar quality of " fire " the
play of prismatic hues, which is the most marked characteristic of
the diamond. It is the difference between the extreme indices of
refraction of the red ray and of the violet ray at the ends of the
visible spectrum. It is best measured by taking as standards
certain fixed lines in the solar spectrum ; but for the purpose of
comparing the dispersive powers of different stones the following
list of approximate dispersion- coefficients (quoted fromM. Jannettaz)
will perhaps suffice :
027
019
015
014
Polarization of Light. There are several ways in which light
may suffer the remarkable change known as polarization. If we
Diamond
Borosilicate of lead
Flint glass .
Blue sapphire
044
049
.036
029
Red garnet
Tourmaline
Crown glass
Rock crystal
PLEOCHROISM. 9
assume that a beam of ordinary or natural light*, freely traversing
any medium, has what we may call identical properties on all its
sides, then, should that beam encounter any obstacle, as by
reflection or refraction, it exhibits to a greater or less extent
different properties on different sides is, in fact, polarized. One
quality of this polarized light is that it cannot be again reflected
at a certain angle, nor can it again traverse in a certain direction
the crystal in which it has suffered this change. But the amateur
of precious stones is mainly concerned with these two facts, that
in some doubly refracting crystalline minerals the two oppositely
polarized beams are of different colours ; and, secondly, that some
transparent gem-stones are more or less opaque, in one direction
at least, to one of the two oppositely polarized beams. Thus it
will be clear that upon double refraction and its concomitant
polarization depends that property of many gems which is known
as pleochroism, and which may be mostly easily recognised
by that useful little instrument, the dichroiscope.
Pleochroism. When a distinctly coloured precious stone is
examined by means of a dichroiscope it will invariably show
two images of the same hue or of different hues. Should the two
images of the square opening of the instrument be identical in
colour," then the specimen may be a garnet, a spinel, or a diamond ;
it cannot be a ruby, a topaz, or a beryl, all of which show twin
colours differing in a perfectly recognizable degree from each other.
However, before proceeding with the description of the special
applications of the dichroiscope, a word on the construction of
the instrument may be introduced. It consists of a cleavage
rhombohedron of Iceland spar, having its longer edges nearly
an inch long and its shorter edges about three tenths of an inch
each. In the original form of the instrument a small glass prism
of 1 8 was cemented on each of the small end faces of the prism ;
but this may be done away with if these end faces be ground and
polished so as to be perpendicular to the length of the prism.
10
PRECIOUS STONES.
A sliding cap at one end has a square perforation of about *I2
inch ; at the other end is a lens, or combination of lenses, of such
focal length as to show a distinct image of the square opening when
the cap is pulled out a quarter of an inch or so. With an instru-
ment so constructed the pleochroism of the vast majority of gem-
stones may be determined at a glance. Of course this quality is
so conspicuous in some species (tourmaline and iolite) that no
instrument is usually needed to discern it. For it is easy to notice
that the colours of some crystals, seen by transmitted light, vary
with the direction in which they are viewed. If the transmitted
ray be analysed by a Nicol's prism, its colour will be found to vary
as the prism is turned round its axis ; in fact, the two differently
coloured beams are polarized in opposite planes. It is of course
only in doubly refracting crystals that this phenomenon of di-
chroism occurs. In the descriptions given further on, of the several
species of stone, these twin colours, as seen by the dichroiscope,
are duly recorded. Here, however, it may be useful to group
a few conspicuous instances of dichroism together ; several are
illustrated by Figs, i to 9 of the Frontispiece.
NAME OF STONE.
TWIN COLOURS.
Sapphire (blue) . .
Greenish straw
Blue.
Ruby (red) . ...
Aurora red .
Carmine red.
Tourmaline (red)
Salmon .
Rose pink.
,, (brownish red)
Umber brown . .
Columbine red.
(brown) .
Orange brown
Greenish yellow.
(green) .
Pistachio green .
Bluish green.
(blue) .
Greenish grey
Indigo blue.
Emerald (green)
Yellowish green .
Bluish green.
Topaz (sherry) ....
Straw yellow
Rose pink.
Peridot (pistachio) .
Brown yellow
Sea green.
Aquamarine (sea green) .
Straw white
Gray blue.
Beryl (pale blue)
Sea green
Azure.
Chrysoberyl (yellow)
Golden brown
Greenish yellow.
Iolite (lavender) , .
Pale buff . .
Indigo blue.
Amethyst (purple) . . .
Reddish purple
Bluish purple.
HARDNESS. ii
When examining a stone for dichroism it is necessary that the
specimen should be looked through in some direction other than
that (along a certain optic axis) in which the crystal is only singly
refracting. Trials in different positions, for the optimum effect,
having been made, the stone should be fixed in such a way that it
can be placed close to the square opening of the dichroiscope. A
disc of millboard having a hole in the middle may be used as a
holder, the specimen being fixed in position by means of a little
blackened beeswax. Then the two images of the square opening
of the dichroiscope should be focussed sharply by means of the
sliding cap. It will be observed that one image of the opening is
nearly central ; this represents the ordinary ray, for which, in the
present volum , the symbol o> is employed. The other image,
formed by the extraordinary ray and expressed by the symbol e,
is more displaced, and is distinguished by a narrow blue border on
its outer edge, and by a narrow red border on its inner edge. On
turning the instrument round the greatest differences of hue between
the two images furnished by a dichroic stone will be seen four times
during a single rotation ; four times the two squares will be identical
in colour^ These phenomena correspond to eight positions, all
45 degrees apart in the circle of 360 degrees. With coloured glasses
and all other singly-refracting substances the images are alike in all
positions.
Further discussion of the optical properties of precious stones,
including the colour-effects produced by diffraction, absorption,
and interference, would be out of place in a handbook of elementary
character. For detailed description of the phenomena in question
reference may be made to any treatise on experimental optics ;
for a brief account the author's little book on " Colour " (Cassell
& Co.) may be consulted.
Hardness. One of the characters by which gem-stones. may be
distinguished from each other and from their^imitations is that of
the degree in which they possess the power of resisting abrasion,
i2 PRECIOUS STONES.
Many hard minerals may, however, be easily broken, fractured, or
chipped, though they cannot be scratched : a very hard stone may
be a very fragile one. Emeralds, zircons, and diamonds have
often been ruined by a fall or a blow.
The scale of hardness adopted for minerals was devised by Mohs.
Fragments of transparent minerals, which may be conveniently
mounted in handles, are applied in succession to the stone under
examination, so as to attempt to scratch its surface. When the
stone neither scratches nor is scratched by any member of the scale,
the hardness of the two stones is the same. When it scratches the
softer, and is scratched by the harder of the two test-stones, some
notion of its position between them may be gained by passing all
three specimens, with slight pressure, over the surface of a fine,
clean, hard file, one end of which rests upon the table, and noting
their different degrees of resistance to abrasion and the sounds
produced. In chapter vii. of this book will be found, under the
description of each kind of precious stone, numbers which nearly
represent the average hardness of good specimens of the several
sorts according to the common mineralogical scale, which
is
Diamond . . . .10
Sapphire .... 9
Topaz . ... .8
Quartz .... 7
Apatite . '.. ' V . 5
Fluorspar . . . . 4
Calcite .... 3
Rock Salt or Gypsum . 2
Felspar . ... 61 Talc . ; . . , . . 1
A list of the degrees of hardness of a considerable number of
different gem-stones will serve to show their relative positions with
regard to this scale. Although this character of hardness cannot
be extensively used in the discrimination, of cut and polished gem
stones, yet it is sometimes available even in the case of such speci-
mens when unmounted, the " girdle " of the stone offering a suitable
surface for a trial of hardness.
Diamond .
Sapphire and Ruby .
Chrysoberyl
Spinel
Topaz . .
Aquamarine . .
. 10-0
. 9-0
. 8-5
. 8-0
. 8-0
. 7'8
lolite ,, .
Cinnamon stone
Jadeite .
Amethyst . . .
Peridot .... .
Jade .
Emerald .
Zircon
Tourmaline
Phenakite
Almandine
. 7-6
. 7-5
. 7-5
. 7'5
. 7'5
Moonstone
Green garnet .
Turquoise . . .
Opal
Lapis-lazuli
SPECIFIC GRAVITY. 13
TABLE OF HARDNESS. +
7-3
7-0
7-0
7-0
6-5
6-2
6-3
6.0
6-0
6-0
5-2
As the property of hardness is of great value in the case of precious
stones, those kinds which are scratched by quartz, and which,
consequently, are below 7 degrees of hardness, are ranked as half-
hard, or " demi-dures." Stones scratched by a knife are below
5 degrees.
There are two remarks as to degrees of hardness which it is
proper to introduce in this place. Firstly, the degree of hardness
of a crystal or a cut stone varies, generally, however, within narrow
limits, on different faces and in different directions. Secondly,
the usually accepted scale of hardness is one having very different
values for the different intervals. Unlike the degrees of the
thermometer where the interval between one degree and the next
above it or below it has the same value, whatever part of the scale
be chosen for comparison, the degrees of hardness on Mohs' scale
show extraordinary divergences.
Specific Gravity. The most generally applicable of all modes
of discriminating precious stones from one another is to ascertain
their specific gravity that is, the relative weights of equal bulks
the weight of a bulk or volume of distilled water (commonly taken
at 60 F. or I5'6 C.) being employed as the unit with which all
the others are compared. There are three modes of ascertaining
the specific gravity of a stone : (i) By placing it in heavy liquids of
known specific gravity, and noting the position which it takes up.
(2) By weighing it in air, and then in water (or other liquid), and
I 4 PRECIOUS STONES.
thus learning the weight of water which the stone displaces that
is, the weight of an equal bulk of water. (3) By measuring or
weighing, directly or by difference, the water which the stone dis-
places when immersed in water in a small vessel of known capacity.
We will now briefly describe these three methods.
i. Several different liquids have been used for the purpose of
ascertaining the density of minerals, and even for separating species
having different densities from one another. One of these liquids,
which has done good service in its day, is a saturated solution of
potassio-mercuric iodide. This may be prepared so as to have a
density of 3*18 at 15 C. It is a yellow liquid called after its dis-
coverer Sonstadt's Solution. Unfortunately this liquid is very
poisonous and rapidly destroys, by amalgamating the metal, any
brass apparatus with which it may come into contact. Two sub-
stitutes for this liquid are now in use. One is an aqueous solution,
which may be diluted at will with water, of the compound known
as cadmium boro-tungstate. The crystals of this salt, to which
the formula Cdj W a B 2 O 31 , 2 H 2 O + i6aq. has been assigned, when
fused, over a water-bath in their own water of crystallization,
yield a liquid which at 75 C. has the specific gravity 3 '55. At
22' C. this cadmium tungstoborate in crystals requires but i-ioth
of its weight of water for solution : a very small further addition
of water enables one to secure a solution which at 15 C. presents
the specific gravity of 3*28. The other heavy liquid to which
reference has been made, as a second substitute for Sonstadt's
Solution, is methylene iodide, the formula of which is CH 2 L.
This compound has the density of 3 32 at 15 C. Its density may
be lowered by the addition of toluene, which, at the same tempera-
ture, has the density 0*869. On the other hand, the density of
methylene iodide - may be raised by saturating it with iodoform
(C H I 3 ) and iodine. It is well to be content with the addition of
iodoform only, for iodine makes the liquid too dark in colour for
the movements of a stone put therein to be observed. It will be
SPECIFIC GRAVITY. 15
seen that we have now at our disposal liquids* which present a
range of density sufficiently wide to permit of the identification of
minerals having densities up to about 3*4: and this result can be
achieved without having recourse to those liquids which need to
be warmed above 15 C. in order to maintain them in a liquid con-
dition. It ought to be mentioned that the methylene iodide pre-
parations, owing to their volatility and to their high coefficient of
expansion when heated, yield results, which, in the absence of the
necessary precautions, may easily be somewhat inexact.
In order to furnish a liquid which will enable one to deal with
stones having a density above 3*4, the double nitrate of thallium
and silver may be taken. It is better to purchase this salt ready
prepared, but it may be made by melting together 150 grams of
crystals of commercial thallium nitrate and 64 grams of silver
nitrate along with a little water and heating the mixture with con-
stant stirring until the temperature of 70 C. has been reached. It
is possible thus to obtain a liquid which at 75 C has a density of
4 '8, but in practice this figure need not be reached. It must be
remembered that all the dilutions of this liquid have one common
property they are poisonous ; moreover they stain the skin a
dark slaty purple not easy to remove.
For the purpose of the collector and connoisseur in precious
stones it will suffice to have at hand the follows six heavy liquids :
A. Thallium and silver nitrate solution of specific gravity 4 '5 maintained
at a temperature well above its fusing point.
B. Thallium and silver nitrate solution of specific gravity 4'1 maintained
at a temperature well above its fusing point.
0. Thallium and silver nitrate solution of specific gravity 3 '9 at 15 C.
D. Thallium and silver nitrate solution of specific gravity 3*5 at 15 C.
E. Cadmium boro-tungstate solution of specific gravity 3 '28 at 15 C., or
methylene iodide slightly diluted with toluene.
F. Cadmium boro-tungstate solution of specific gravity 2*67 : this is pre-
pared by diluting E. with water until a fragment of beryl sinks and a
fragment of amethyst floats therein. Or methylene iodide, diluted with
toluol to the same density and with the same indicators, may bq
substituted,
i6
PRECIOUS STONES.
The stone to be determined should be first placed in liquid
A, in which all stones but red, dull-green, puce, yellow, white,
and brown zircons will float. After removal from A, washing
with hot water and wiping dry with a cloth, the stone (which has
not sunk in A) is placed in liquid B, where, if it sinks, it may be
almandine, spessartite or golden -zircon. Should it not sink,
it is transferred with due precautions to C. Here, if it sinks, itmay
be ruby, sapphire or one of the other varieties of corundum, or
possibly a green zircon. If, however, the stone floats in C it may
belong to one of the much larger groups, with which we will now
endeavour to deal in a tabular form :
In solution D
Diamond }
Topaz
Spinel
sink
In solution
Jadeite
Diopside
Peridot
Chrysolite
sink
sink, while
float
Chrysoberyl
Alexandrite
Pyrope
Demantoid >
In solution F
Beryl
Emerald
Turquoise
Phenakite
Jade
Tourmaline
Spodumene
Much may be learnt by the behaviour of a stone in the liquid
employed. It may sink or rise slowly when its specific gravity is
near that of the liquid, or it may remain, as it were, suspended in
the midst, in cases where its density is the same as that of the
liquid. Before using any of the solutions their specific gravity
should be carefully determined , they must be preserved from
/Opal
Moonstone
' Lapis-lazuli
lolite
Amethyst
SPECIFIC GRAVITY. 17
dust, evaporation, etc., in suitable stoppered ancf capped bottles
or short wide tubes in the case of A and B. A number of weighted
glass bulbs or a series of small mineral fragments of ascertained
specific gravity are very useful as " indicators." It is a good plan
to keep one or more of these indicators in each liquid to be employed.
To avoid doubt and confusion these indicators, whether bulbs or
mineral fragments, should present so characteristic a form or colour
or marking that their identity and value can be recognized at once.
It is worth while adding the remark that liquids A, B, and C, are re-
quired much less frequently than the less dense liquids, and that
when the position of a doubtful stone has been once fixed by the
density test so as to prove that it belongs to a particular group,
then it may be necessary to call in the aid of the dichroiscope and
of the scale of hardness in order to learn to what species in that
group the stone really belongs.
2. By weighing a stone in air and then in some liquid of known
density, the weight of the bulk of the latter displaced by the stone
is ascertained. If, for example, a sapphire weighing 4 grains in
air weighs but 3 grains in water, it has evidently displaced i grain
of water, becoming lighter by that amount. So the number 4
represents the specific gravity of sapphire, showing, as it does, the
number of times that the weight of any bulk of that stone contains
the weight of an equal bulk of water. An example of an actual
experiment of this kind will serve to illustrate this, the ordinary
method of taking specific gravities, better than any further ex-
planation of the principle involved.
A yellow sapphire weighed in air . . 12.896 grams.
water . 9.677
Difference, that is, weight of water displaced 3-2IQ
The proportion will be :
VVt. water displaced. Sp. gr. water. Wt. sapphire. Sp. gr. sapphire.
3-219 : 1 12-896
x .= 4-006
8445.
i8 PRECIOUS STONES.
There are several corrections which are needed before an exact
result can be reached. They are these : Firstly, the stone and
the water must be compared at the same temperature, usually
that of 60 F. or 15 '6 C. This is the most important correction
and the only one usually applied ; it is well to avoid the necessity
of introducing it, by conducting the experiment at the standard
temperature. The second correction originates in the fact that
the stone is weighed in air, and consequently is buoyed up to some
extent by that fluid, appearing lighter than it would be if weighed
in vacno. The third correction depends upon the material of the
weights. These, if of brass, displace from one-half to one-third
of the amount of air displaced by the stone in the other pan of the
balance, and consequently involve another error. The several
corrections we have named may be learned with sufficient accuracy
by the following methods : The correction for temperature may
be applied by multiplying the difference between the weight in
air and the weight in water, not by unity, but by the actual specific
gravity of water at the observed temperature,* then proceed with
the calculation as before. The correction on account of the air
and the brass weights is given by the formula :
y = w -0012
(a - ' 12 )
where w is the observed weight in air of a given substance ; d its
approximate specific gravity ; * 0012 the mean density of atmo-
spheric air ; * 12 the reciprocal of the specific gravity of brass, and
* If the specific gravity of water at 4 C. be taken as 1,
gravities at higher and lower temperatures will be :
then the specific
99987
7
99993
14
99930
1
99993
8
99989
15
99916
-2
99997
9
99982
16
99900
3
99999
10
99975
17
99884
4
1-00000
11
99966
18
99865
5
99999
12
99955
19
99846
6
99997
13
99943
20
99826
SPECIFIC GRAVITY. IQ
y the weight by which the substance when weighed with brass weights
will appear too light. The true weight, W, in vacuo will then be :
W = w + y
Now, with the true weight, W, in vacuo, the specific gravity
may be calculated according to the equation previously given.
To furnish a notion of the value of this correction, it may be stated
that a fragment of rock crystal weighing 10 grams will become
10*0031 grams, a grain of 3 parts in 10,000.
When the specific gravity of a small gem is to be taken, an assay
balance of great accuracy may be advantageously employed. f
In this case the full advantage of the delicacy of the instrument
cannot be secured if water, which has a high surface-tension, be the
liquid in which the stone is weighed, the friction between it and the
stone and immersed pan being too great. Alcohol considerably
diluted with water answers well. A fair quantity is prepared and
preserved in a well -stoppered and capped bottle. Its specific gravity
is best ascertained by means of Dr. Sprengel's tube. In the follow-
ing example of an experiment a dilute alcohol of sp. gr. '8488 at
15 C., and containing about 80 per cent, by weight of absolute
alcohol, was used :
Specific gravity of brilliant-cut specimen of phenakite.
Weight in air . . . i . 1294 gram.
,; alcohol at 15 C. 0.8064
Alcohol displaced 0.3230 ,,
The equation will be :
1 -12Q4 x -8488
. 3 * 3 = 2-9676 = sp. gr. of phenakite.
The one objection to this use of diluted alcohol consists in the
tendency which it has to change its density by loss of alcohol ; on
this account pure toluene, a liquid hydrocarbon, having a density
of '869 at i5C., affords a convenient substitute for spirit.
t M. Jolly's spring balance, as modified by Mr. C. F. Cross, is another
useful form of instrument for this purpose.
8445. B 2
20
PRECIOUS STONES.
3. The third method of taking specific gravities does not admit
of great exactness. A small wide-mouth bottle or beaker, with
a ground rim and ground glass cover, both truly plane, is filled
with water, the cover placed in position, avoiding air-bubbles
and wiping off any water outside the vessel, and then weighing
it and its contents. Let this weight be x. Now introduce the
gem and replace the lid as before ; let the present weight be y,
and that of the gem in air w ; then approximately,
= sp. gr.
w + x y
In employing this method the vessel used should be no larger
than will contain the specimen.
Specific gravities may be ascertained by means of contrivances
dependent upon the measurement of the liquid the objects dis-
place from a vessel of known capacity or carefully graduated. The
space at our disposal will not allow of any further details on this
subject. But a caution as to the necessity in all specific gravity
experiments of getting rid of air-bubbles may not be out of place.
To attain this end boiled water should be used, and if mechanical
contrivances fail (a feather or sable pencil) then the liquid and
stone should be placed under the receiver of an air-pump and the
air exhausted.
Details concerning the specific gravity of each kind of precious
stone will be found in chapter vii. The following table gives a
fair number of average densities arranged in regular sequence :
FOUR AND ABOVE,
Haematite
Pyrites . .
Zircon
Almandine
Sapphire .
THREE AND
ABOVE.
TWO AND
ABOVE.
5-3
Green garnet
. 3-85
Phenakite .
. 2-98
5-2
Chry so beryl .
. 3-76
Turquoise
. 2-75
4-6
Pyrope .
. 375
Labradorite .
. 2-72
4-2
Hessonite
. 3-66
Beryl .
. 2-70
4-0
Spinel .
. 3-65
Amethyst
. 2-66
Topaz .
. 3-55
Rock crystal .
. 2-65
Diamond
. 3-52
lolite .
. 2-63
Peridot .
. 3-38
Moonstone .
. 2-58
Spodumene .
. 3-20
Opal
. 2-20
Tourmaline .
.. 3-10
LUSTRE. 21
The following brief notes as to the physical or* mechanical pro-
perties of minerals not already discussed or described must suffice .
Form. The forms of crystals are all referable to one or other
of these six crystallographic systems, (i) The cubic or monometric;
(2) the pyramidal, dimetric, or tetragonal ; (3) the rhombohedral
or hexagonal ; (4) the prismatic, trimetric, or orthorhombic ; (5)
the oblique or monoclinic ; (6) the triclinic or anorthic.
Structure. The mode of mechanical aggregation or intimate
texture of minerals may often be learnt by disruption of the mass,
or by splitting or cleaving it. Structure is often crystalline, laminar,
fibrous, or columnar. Fractured, not cleaved, surfaces are less
instructive they may be conchoidal, uneven, splintery, or hackly.
Transparency. For want of a more comprehensive term, the
various degrees of resistance to the transmission of light through
minerals are included under this title. The degrees are five :
Transparent when objects can be seen distinctly.
Semi-transparent when objects can be seen dimly.
Translucent when light, not objects, can be seen.
Subtranslucent when light is transmitted through thin
splinters.
Opaque when light is not transmitted.
Lustre. This character, although it needs some practice to
discern it accurately, is of importance as an element not merely of
the, beauty but also in the discrimination of precious stones. The
terms employed to designate its various qualities are these :
Metallic, as on pyrites.
Adamantine, ,, diamond.
Resinous, ,, garnet.
Vitreous, ,, emerald.
Waxy, turquoise.
Pearly, moonstone.
Silky, crocidolite.
22
PRECIOUSVSrONES.
Metallic and adamantine lustres are connected with high re-
fractive indices. The colours of precious stones are discussed in
chapter iv.
In the five tables which follow have been arranged certain physical
data of precious stones so that they may be discriminated from one
another by comparing their specific gravities, their behaviour when
examined with the dichroiscope, and their hardness.
DISCRIMINATION OF PRECIOUS STONES.
WHITE STONES.
NAME.
I
DENSITY.
j PLEOCHROISM.
HARDNESS.
Opal , . - / . . .
2-20
N(
me 6
Moonstone . . .
2-58
6
Rock-crvstal . . .
2-65
7
Beryl ". . . . ..
2-69
7|
Phenakite . .
2-98
: 7|
Diamond . . . .
3-53
10
Topaz . . . ...
3-57
8
Sapphire . . . '' *
4-00
9
Zircon . . . ...
4-75
74
RED AND PINK STONES.
NAME.
DENSITY.
PLEOCHROISM.
HARDNESS.
Tourmaline . . . -i.
3-05
Strong
71
Kunzite . . . ' .
3-18
,,
6f
Topaz . . . : .
3-53
,,
8
Spinel . . ...
;}-58
None
8
Pyrope . ...
3-75
,,
74
Ruby . . .
4-00
Strong
9
Almandine .
4-15
None
71
Zircon . ...
4-70
Weak
H
DISCRIMINATION OF PRECIOUS STONES. 23
ORANGE AND YELLOW STONES. ^
NAME.
DENSITY.
PLEOCHROISM.
HARDNESS.
Cairngorm . . .
2-66
Weak
7
Beryl . ' . . . . ' ..
2-69
Strong
71
Tourmaline . .
3-11
,,
74
Spodumene . . . .
3:20
Weak
6?
Diamond . .
3-53
None
10
Topaz . . . '
3-53
Strong
8
Hessonite . . .
3-66
None
7
Chrysoberyl . . . .*'.'
375
Strong
84
Sapphire . , . . . ~
4-00
,,
9
Spessartite . . . .
4-15
None
7i
Golden Zircon . . .'
4-40
Weak
7
Yellow Zircon . . : .
4-67
M
7i
GREEN STONES.
NAME.
DENSITY.
PLEOCHROISM.
HARDNESS.
Emerald
2-70
Strong
71
Aquamarine . . .
2-70
71
Jade
3-00
Distinct
6
Tourmaline .
3-11
Strong
7|
Hiddenite
3-15
it
6|
Jadeite
3-32
Distinct
7
Diopside
3-34
Weak
6
Peridot ....
3-40
Strong
6J
Epidote ....
3-44
>
6i
Spinel .
3-58
None
8
Alexandrite .
3-65
Strong
8*
Demantoid .
3-85
None
6
Sapphire
4-00
Strong
9
Zircon ....
4-05
Weak
u
PRECIOUS STONES.
BLUE AND VIOLET STONES.
NAME.
DENSITY.
PLEOCHROISM.
HARDNESS.
Lapis-lazuli .
lolite :
2'40
2-63
None
Strong
u
Amethyst . . .
Beryl .
2-66
2-69
Weak
Strong
7
71
Turquoise
Tourmaline .
2'75
3-10
None
Strong
6
Topaz ....
3-55
,,
8
Spinel . .
3'65
None
8
Sapphire , .
4-00
Strong
9
Zircon ....
4-65
Weak
74
On pages 6 to 20 there have been described easy methods of ascertaining the
density, pleochroism and hardness of precious stones. The index of refraction
may also now be determined, thanks to Mr. G. F. Herbert Smith's improved
Keiractometer, which is available for all gems of which the index of refraction
lies between T45 and T74. The instrument, as made by Mr. J. H. Steward, is
accompanied by instructions how to use it and how to interpret the observations
made ; also by a table of indices corresponding to each division of the graduated
scale. The Refractometer is standardized for use with the yellow light of a
sodium flame, but white light may be employed if approximations suffice.
Place a small drop of a highly refractive liquid a bromonaphthaline, for
example upon the plane surface of the hemispherical lens. Then press a flat
face of the gem into the liquid, so that the latter has a uniform thickness.
Light being admitted through the ground glass " window " of the instrument,
and the scale focussed, it will be seen that different parts of the scale are
differently illuminated ; the edges or boundaries of these regions where they
coincide with the scale-divisions are to be noted. With glass and other singly-
refracting substances, the edges due to these solids are single, with doubly-
refracting minerals double. It is essential that the edge arising from the
refractive liquid itself should be beyond the edge due to the stone. So when
spodumene, peridot and spinel, with indices ranging between 1 *65 and 1 '73, have
to be tested, methylene iodide, with a refractive index of 1 "74, must be substi-
tuted for bromonaphthaline, the refractive index of which is only 1 '658.
CHAPTER III.
CUTTING AND FASHIONING PRECIOUS STONES.
VERY few precious stones, as we receive them from the hands of
nature, present the beautiful qualities for which we look in these
concentrated treasures of the earth. Often they are waterworn
pebbles, roughened by attrition and blows during years or even
centuries of wanderings in the beds of streams and rivers. If we
find them intact in their rocky homes, they are oft-times obscured
with flaws and intruding matters which mar their beauty. If trans-
parent and without speck or fracture, yet the natural forms in
which crystallised gem-stones occur are but rarely adapted for
direct employment in objects of jewellery. In shape or size they
are awkward for such use, while many of those marvellous optical
qualities which distinguish them from the crowd of commoner
materials are brought into prominence only by the artificial
processes of cutting and polishing. These processes convert
rough crystals into shapely gems, having fine qualities of
surface lustre and interior colour, and, withal, much less
liable to fracture than the original stone. Now and then
a perfect natural octohedron of flawless diamond or rosy
spinel may be set in a ring or jewel ; but such instances
are exceptional, and gem-stones, in order that all their
elements of beauty may be developed to the uttermost, must
be cut and polished according to rule.
All the different forms into which precious stones are cut may
26
PRECIOUS STONES.
be arranged into the two groups (i) those having plane surfaces ;
(2) those having curved surfaces : but, under special circumstances,
facets or plane surfaces are occasionally associated with curved
surfaces in the same specimen. The further subdivision of the
two groups of forms may be tabulated thus :
Group 1. Plane surfaces
Group 2. Curved surfaces
Brilliant-cut.
Step or trap-cut.
Table-cut.
Rose-cut.
Single cabochon.
Doable cabochon.
Hollowed cabochon.
Tallow top.
A few words descriptive of each of these modes of cutting stones
may now be given.
The old brilliant-cut, though susceptible of many small modifi-
cations as to the size of the facets, their mutual proportions and
inclinations, and even their number, requires, when perfect, 58
facets thus arranged :
1 Table
8 Star facets
4 Templets or bezels
4 Quoins or lozenges
8 Cross or skew facets 1
8 Skill facets*
33
The
" Crown,"
or upper
part of the
brilliant.
Fig. 12.
* The cross and skill facets are sometimes called half-facets ; the former
are known as cldtures by the French lapidaries.
BRILLIANT-CUT.
2 7
1 Culet or collet
4 Pavilion facets
4 Quoins
8 Cross facets
8 Skill facets
= The " Pavi-
lion," or base,
or under part
of the brilliant.
Fig. 13.
There are thus 58 facets in a brilliant, while the " girdle " or
edge bounding the widest part of the stone divides the crown from
the base, and is concealed, in part at least, by the mounting or
setting. This girdle must not be very thin (it is liable to be so
in what are called " spread," that is, shallow, stones), for then it
may become chipped and break away during mounting. If it be
thick, on the other hand, the brilliancy of the stone is lessened,
and its material wasted by the concealment of a good deal of it in
the mount. This form of cutting is reserved particularly for the
diamond so much so, that the word "brilliant" used alone
signifies a diamond cut after this fashion. Of late years the girdle
of brilliants has been made to approach a circular outline ; the
templets and quoins are nearly of the same size, and eight star
facets are cut round the culet, thus making a stone of 66 facets.
Certain rules have been laid down for the relative proportions,
not only of the several classes of facets in a brilliant-cut diamond,
but also for the thickness of the finished stone in each and all its
diameters. Thus i-3rd of the total thickness should be occupied
by the crown or upper portion above the girdle, 2-3rds being below.
The table should be 4~9ths of the breadth of the stone, and the
PRECIOUS STONES.
culet i -6th to i-5th of the table ; bu-t according to some modern
experts, both these facets, but chiefly the former, may be reduced
with advantage below these proportions. Two of the most famous
diamonds of the world show large departures from the typical
proportions of a brilliant : The Koh-i-nur in its present form is
far too broad for its depth or thickness ; the Regent is a good deal
too thick for its breadth. But the same rule of proportion, although
it may hold good for such diamonds as admit of being subjected to it
without extravagant loss of weight, must be modified with stones
of other species, and especially with coloured stones. With colour-
less topazes, sapphires, etc., the surfaces and inclinations of the
facets must be modified to suit the refactive indices and other
optical constants of these minerals ; with coloured stones, if pale
(certain alexandrites for example), greater depth must be secured ;
if dark in hue, then greater " spread " and less depth (deep red
garnets furnish instances).
The style of cutting known as the step-cut or trap-cut is adopted
for the emerald and many coloured stones. It is subject to rules
of proportion far less strict than those devised for the cutting of
the diamond in the brilliant form. Each species of stone needs
special study, that the typical step-cut
may be so modified as to bring out the
full beauty of the gem. The fault most
common with step-cut stones is the too
great breadth of the table, for the in-
ternal reflections from the lower facets
are best seen through the sloping bezels
of the crown, not through the flat sur-
face of the table. In the step-cut (fig.
14) we have then a table, two or more
sloping step facets, and then the girdle,
while the lower part of the stone (fig. 15)
is cut into three or more sets or zones of Fig. 15.
Fig. 14.
CABOCHON. 29
diminishing steps, with an oblong square or Hexagonal or octagonal
culet as termination. Some trap-cut stones are brilliant cut below
the girdle, or vice versa.
The table-cut needs little description : it has a very largely
developed table with bevelled edge, or a border of small facets.
It is employed ioi covering fine gold-work and miniatures ; in
the sixteenth century and later it was used in Europe for much
diamond-work.
The rose-cut (fig. 16) shares with the table-cut a much greater
antiquity than the brilliant-cut. It may be
compared with the latter by supposing the table
to be replaced by six triangular or star facets,
and the crown to be represented by eighteen tri-
angular cross and skill facets which together con-
stitute what the French call la dentelle. The F - 1( ,
base is either flat or a duplicate of the upper part.
The other forms given to faceted stones are not of sufficient
importance to need description ; the star-cut and the pendeloque
may just be named as patterns sometimes followed in the cutting
of diamonds.
Translucent and opaque stones are commonly cut en cabochon
(fig. 17); the opal and the turquoise are
characteristic examples. The moonstone,
avanturine, cat's-eye, and star sapphire, too,
would not show their peculiar properties were the
confusing reflected lights from facets to be
mingled with the white sheen, the brilliant
spangles, the silver thread, or the six-rayed
star which these stones respectively present
when properly fashioned. The one transparent
stone which is frequently cabochon-cut is the
garnet, which is then called a carbuncle. A
variety of cabochon used for this gem is
30 PRECIOUS STONES.
somewhat hollowed behind (fig. 19), to receive a piece of foil as
well as to lessen the depth of colour in very dark stones. Our
figures represent the simple cabochon (fig. 17), the double cabochon
(fig. 18), the hollowed (tvidt) cabochon (fig. 19),
and the flattened form much used for opals,
and called tallow-topped (fig. 20). The double
cabochon is usually cut with the base of lesser ' Fi^ 19
curvature than the crown ; but with many
stones a more brilliant play of coloured light
within the stone may be secured by reversing
these proportions. Although the cabochon
form is almost essential to many precious Fig. 20.
stones, and is useful to hide the poverty and
flaws of others, and also is convenient in the case of stones to be used
in the decoration of vases and other objects to be handled, yet it
ought not to be allowed to displace the various faceted forms.
Doubtless there is a quiet beauty and richness in a good cabochon
ruby, sapphire, emerald, or jargoon, but we lose some of the most
striking characteristics of these gems when we so cut them as not
to admit of the display of their dichroism, and their dispersive
and reflective powers. The narrow view that all faceted stones
are vulgar is based on caprice and ignorance ; it is the mere un-
intelligent whim of a clique of artists and amateur writers on art.
For the faceting of the great majority of transparent stones is an
operation necessary for the development of those optical qualities
upon which the beauty of precious stones mainly depends. It
should be performed in strict accordance with certain rules of
proportion, which may be deduced from the optical constants of
each species of stone.
Information as to the mechanical processes and the materials
employed in the cutting and polishing of precious stones may be
found in the works of Jannettaz and Dieulafait. Horizontal
wheels of steel, gun-metal, copper, lead, pewter, tin and wood
CARBORUNDUM. 31
charged with various grinding and polishing pofvders, are employed
for different stones, and in different stages of the operations. The
wheel, or disc, or lap as it is called, is usually horizontal and is
made to revolve with great rapidity. The grinding or polishing
powder, mixed, according to its nature, with olive oil or water,
becomes partially embedded, in the lap. This powder, in the case
of diamonds, must be of diamond itself, generally in the form of
boart, a dark and rather porous variety of the mineral. The com-
paratively new and artificial compound of silicon and carbon
known as carborundum is now largely used in the case cf the harder
stones, but emery, garnet-powder, tripolite, rotten stone, jeweller's
rouge, pumice, putty-powder, and bole are in constant requisition
for the grinding and polishing of stones less hard than the diamond.
The whole subject of this mechanical treatment of stones, including
splitting, dividing and shaping operations, is one which cannot be
discussed here, involving as it does a large number of minute tech-
nical details of no interest from an artistic standpoint.
CHAPTER IV.
ARTISTIC EMPLOYMENT OF PRECIOUS STONES.
SOME acquaintance with the less obvious characters and qualities
of precious stones, and especially with the distinctive properties
of those kinds which remain practically unrecognised and unap-
preciated, may serve more than one good purpose. Not only may
the jeweller's art receive new impetus and suggestion, but the
buyers and connoisseurs of bijouterie may learn to appreciate
more highly well- conceived design, new combinations, and ex-
quisite workmanship. Most admirable and pleasant colour-com-
binations may be attained by the aid of materials which in many
instances are now by no means costly. Curious and delicate hues
of luminous and refined quality, preserved in enduring substance,
may be arranged and grouped in forms of endless beauty and
variety. Neither silks, nor paints, nor even enamels can ever
equal the colours of precious stones in durability, or in brilliancy
and pulsating variety of hue. And it cannot be doubted that
when knowledge of the true nature of any art material (such as
precious stones) becomes more intimate, exact, and diffused, a more
intelligent and lively interest will be created in examples of good
work wrought in the substance in question. Every connoisseur
or collector of artistic objects must have shared in experiences of
this kind. He may have been once quite dead to the peculiar
merits of certain works, say in bronze, not even glancing at any
specimens falling in his way. Then some casual circumstance,
perhaps an exciting contest for a fine piece of work at a sale
APPRECIATION OF PRECIOUS STONES. 33
between two enthusiastic collectors, or perhaps 'the gift of a choice
specimen, may have drawn attention, not perhaps to the merits of
such specimens, but at least to the esteem in which they may be
held. Curiosity it may be an intelligent curiosity is excited.
Investigation, more or less searching, follows. The hardness of
the metal, its provenance, its designer, its age, the mode of manu-
facture, whether by casting or hammering ; the manner of decora-
tion, whether by chasing, engraving, or inlaying ; the colour and
texture of the surface, the presence or absence of patina ; and not
a few other points of interest, constitute the materials of complex
study. Study provokes observation, and observation study, so
that before long the neglected group of artistic bronzes exerts a
kind of fascination upon the new votary. If his knowledge be
superficial and inaccurate, or if he be merely an ameteur or col-
lector just because it is a fashionable pursuit to gather together
or to admire certain classes of artistic objects, well then, he does
not really know what and why he admires. Forgeries delight
him just as much as genuine works, so long as he is not sure that
they are forgeries ; but he has not sufficient patience for the
mastery of, or sufficient insight into, the characteristics of true
productions to discriminate them from those that are false. It
often happens thus with the amateur of precious stones. He
knows nothing of the optical elements, say of surface lustre, and
the pleochroism which go to make up the tout ensemble of any
particular gem, and is quite satisfied with a well-cut bit of paste,
or a cleverly contrived doublet. No doubt, in some cases, even
an educated keenness of vision does not suffice to distinguish the
true stone from the false, although the durability of the genuine
specimens will ultimately prove their superiority. But it is not
difficult to learn to appreciate the peculiar and essential characters
of the majority of the species of precious stones. The few simple
pieces of apparatus and the appliances described in the second
chapter, will serve to supplement and correct the deductions of a
8445. C
34 PRECIOUS STONES.
trained eye and touch. And with a spectroscope, a polariscope,
in addition to a good hand magnifier or pocket lens, such an array
of evidence may be marshalled that there can remain but few cases
in which the identity of a stone shall continue doubtful. But for
the purpose of the artistic employment or appreciation of precious
stones such a table as that given on pages 5 and 6 will prove more
useful than any recondite method of inquiry. Some of the uses of
that tabular arrangement of conspicuous optical qualities may be
gathered from the following examples. Referring to the shape of
stones we note that their boundaries are either plane or curved.
Now if we have to use, in any piece of personal ornament, stones
having curved surfaces, it will not answer in general to associate
with them other curved surfaces, like those of the en cabochon
moonstone ; and especially is this the case where the size of the
stone, as well as the character of the curved surface, is nearly
identical ; but a happier result will be attained by combining a
step-cut stone with one having a curved surface. Again, citing an
example from the series of adjectives expressing qualities of sur-
face, it will be found that gems having an adamantine lustre assort
better with those which present the less brilliant surface known as
waxy, than they do with those which show a nearer approach to
the adamantine surface, and which are called resinous. The
diamond and the jargoon do not improve or bring out each other's
qualities, for they have too many points in common ;- but the
diamond accords well with the pearl, and the jargoon with the
turquoise, that is, the adamantine with the pearly, and the re-
sinous with the waxy. Looking, now, into the substance of stones,
rather than on their surface, their relations to the transmission
of colourless light furnish many illustrations of wise and unwise,
or effective and defective combinations. For example, chatoyant
stones, like cat's-eyes, do not associate well with translucent stones,
like the chrysoprase and the chalcedony the translucency of the
latter confuses, because it resembles too closely, ] the chatoyancy
ARTISTIC ASSOCIATIONS. 35
f
of the former. But transparent stones accord well with all those
which interrupt the passage of light by such internal reflections.
The diamond, on this account, combines admirably with the cat's-
eye and the pearl, but it affords too strong a contrast, especially
when of large size, with the turquoise, to associate pleasantly with
this nearly opaque stone. From amongst the qualities pertaining
tc the colour of stones, examples of the utility of the table may be
cited. When a stone has much " fire " in it- -that is, when its
refractive and dispersive actions upon light are high and it shows
prismatic hues, then it looks best if associated with gems in which
this property is less developed. Again, monochroic stones, which
in all directions transmit beams of the same colour, should be
associated with pleochroic stones, which exhibit two or more hues,
while the latter should not be mixed together.
We are led from the study of these examples of associations
of gem-stones to inquire into the principles which underlie artistic
combinations. Probably we are satisfied with arrangements of
precious stones in which the leading motif is either identity, or
seriation, or contrast. When stones match, when they are gra-
duated, or when they offer a distinct but not startling contrast, the
resulting effect is at least capable of being made satisfactory.
When we speak of identity, seriation, and contrast, as expressing
the elements of decorative association in the mounting of precious
stones, we use words into which we are compelled to import special
meanings. By identity, we mean that very close resemblance
which selected specimens of choice stones of the same kind will
exhibit ; seriation expresses the orderly sequence of tones or
colours with the presence of a pervading and dominant element ;
contrast implies an effect of change rather than of passage , and
may include contrast of tone and of lustre as well as contrast of
colour. Instead of further discussing the question of the artistic
employment of precious stones in precise accordance with the
three principles of association before laid down, a more useful and
8445. C 2
36 PRECIOUS STONES.
generally available plan will be to follow a classification according
to colour. For as the ornamental or artistic employment of
precious stones conveys primarily, if not wholly and ultimately,
an appeal to the eye, it is clear that such optical properties as
can be comprised in the terms lustre, light, and especially colour,
should be our first consideration. After all, as, on the whole, the
prominent feature of precious stones is their colour, so the easiest
way of considering their colour is to adopt the order of succession
of the colours in the ordinary rainbow or prismatic spectrum,
beginning with the white light, which contains them all, and origi-
nates them all.
White Stones. The diamond naturally takes the first position
if we consider its hardness, its remarkable composition, and its
strong refraction and dispersion of light. Its properties, so far as
they appeal to the eye, differ much from those belonging to the
majority of other stones, and it forms, partly in consequence of
this peculiarity, as good a border or setting to other gems as a gold
frame generally does to a picture. Of course much depends upon
the quality of the diamond, and much upon the shape which is
given to it by the lapidary. The flat plates of lasque diamonds,
and, in less degree, the step-cut stones with broad tables, exhibit
the unique and splendid lustre which is peculiar to the polished
surface of this stone ; these forms also permit the transparency
and the total internal reflection of light to be well seen. Even the
form of the diamond crystal, the regular octohedron, when its sur-
faces are really planes, well exhibits the transparency and reflection
of the stone. Next to the diamond we may place the colourless
zircon or jargoon, then the phenakite, then the white sapphire,
the white topaz, and the white beryl. Rock crystal will come
below these in point of beauty and brilliancy. The colourless
zircon sometimes approaches near in prismatic brilliancy to a dia-
mond ; so, at night especially, does the rare and curious mineral
phenakite. There is, however, always a sort of difficulty in finding
WHITE STONES. 37
an appropriate use for colourless, yet lustrous', stones in any article
of jewellery intended for personal adornment. The more lustrous
and prismatic they are the more they resemble the diamond, in
fact the less available are they for the usual purpose to which
gems are put. Still, there are peculiar qualities in these stones
which need not be lost to artistic employment, if the white stones
in question be judiciously associated with materials which pre-
vent their being mistaken for diamonds. A white diamond should
rarely or never be bordered by green tourmalines, but these stones
would form an agreeable combination with a white zircon, a phen-
akite, or a white topaz. In the white sapphire there is often a
faint suspicion of milkiness, and in the white beryl a cool green-
ish tint, which prevent these stones from resembling the diamond
so closely as to be taken for imitations of that gem. But many
of these colourless stones, notably the topaz and rock crystal, in
all probability are most appropriately used when set as bosses in
vessels and other large pieces of metal work, or employed in the
form of plaques for engraving or etching. It is scarcely neces-
sary to justify such uses of these minerals, and this is not the place
to enter upon the question, particularly as it is only by a rather
wide use of the term precious that I am able to include these
materials, and some others which I shall have to discuss presently,
amongst precious stones. Of two other white materials em-
ployed in jewellery, the moonstone and the pearl, a few words may
be introduced here. The moonstone forms an excellent substi-
tute in many combinations for the pearl, but it does not associate
so well as the latter with the diamond. With deep-coloured
amethysts, spinels, and tourmalines, few colourless gems look
more refined than the moonstone. But these stones, which fetch
a shilling or so apiece only, should always be accurately recut and
highly repolished before being used. Their forms are too irre-
gular and their surfaces too imperfect, as imported from Ceylon,
to show off their moonlight sheen with half its intensity, unless
38 PRECIOUS STONES.
they are passed again under a careful lapidary's hands. The
improvement thus effected is marvellous. The value of the pearl,
whether its " orient " be luminous with prismatic hues, or whether
it be a warm soft white merely, is too well known to be more
than named in this connection. But we may be permitted to say
one word in deprecation of the extravagant expenditure of time,
of ingenuity, and of costly materials, which the attempt to convert
large irregular pearls into structures resembling figures has so
often caused. The result is nearly always most unhappy.
Red Stones. The ruby may fitly be considered before other
coloured stones. It, with the sapphire, and all the transparent
varieties of corundum, ranks next to the diamond in hardness.
It is, moreover, a stone of great beauty. Probably the experts in
jewels are right in assigning the highest value to those rubies
which possess a " pigeon's blood " colour this is the orthodox
hue. But the paler colours, and those which verge upon pink
and crimson, and even violet, are capable of being so treated by
means of association with white and black enamel or with dark
stones, like olive-green tourmalines, as to lend themselves to the
production of very beautiful decorative effects. The great mistake
commonly made in the treatment of the paler rubies lies in the
attempt to treat them in the same way as the deeper coloured
stones.
It is difficult to describe the peculiar colour quality of the ruby
in words. In fact, our nomenclature of colours is neither ample
nor accurate. Our appreciation of delicate differences between
colours is growing, but the language by which we endeavour to
describe the hues which we have learned to appreciate is either
stationary, or else receives additions from time to time of unsatis-
factory words, derived from the caprices of French fashions. The
time has really arrived when a standard series of hues of all sorts
should be constructed and appropriately named ; but, in the case
of the ruby, the question of pleochroism comes in, and renders
RED STONES. 39
the difficulty of describing the colour quality ^f this stone greater.
There is also some prismatic " fire " in the stone, and much in-
ternal reflection of light, while its surface lustre lies between re-
sinous and vitreous. These four properties give to the red of
the ruby a peculiar richness, which the two other species of pre-
cious stones the spinel and the garnet which come nearest to
it in colour, do not equally possess. The two reds which make
up the colour transmitted by the ruby do not differ much, but yet
they help to impart, to a properly cut stone, a delicate variation of
hue which is not present in any other red stone, nor in any imitative
substance. The dichroiscope, consequently, never fails to discri-
minate between a ruby on the one hand and a spinel or a garnet
on the other. The two latter stones are, of course, softer than
the ruby, and the former is always lighter, that is, of less specific
gravity. For the ruby and the whole of the corundum family of
stones have the specific gravity of 4, and a hardness which is
nearly, and in some cases quite, 9 on the mineralogical scale.
One of the happiest uses of the ruby is in the form of an inlay,
in certain gold vessels of Indian origin. The external surface of
these vessels is covered with a system of interlacing ridges and
furrows. The rubies, generally small, oval, and cut en cabochon,
are set along the furrows. Thus they are much protected from
the chance of dislodgment, while the effect they produce, of a
rich deep crimson groundwork over which a gold netting has been
thrown, is in perfect harmony with the materials and their work-
manship. For, naturally, the metal gold, when pure, or nearly
pure, throws a ruddy tint when light is reflected from surface to
surface ; witness the interior of gilt vessels. The same thing
occurs in the golden furrows of which we have spoken, where the
rubies seem to rest in a golden sheen, of a hue in which the yellow,
and orange, and red elements, now one and now another, appear
to prevail. The gold should not be burnished where much con-
trast between the metallic surfaces and the rubies is desired, but
40 PRECIOUS STONES.
the stones themselves should be as brightly polished as possible,
in order not only to develop the full beauty and variety of their
colour, but also the very considerable surface lustre which the
ruby possesses. There is another kind of Indian jeweller's work
to which most of the remarks I have just made apply. A per-
forated plate or disc of delicate arabesque or radiated work is
found decorated with ruby beads, round or oval, attached to the
circumference of the ornament, or else introduced into its midst
in concentric circles. Here dull dead or " matt " gold is par-
ticularly appropriate, as affording a pleasant contrast to the rich,
smooth, and soft transparency of the rubies, which, from the
manner of their mounting, may be looked through. The refine-
ment of the slender gold-work, which, in this class of jewellery,
approaches the delicacy of filigree, sets off by its minuteness of
detail the simpler and bolder forms of the plain, smooth, rounded
stones, which give it colour and warmth. We must dwell for a
moment or two upon another Eastern method of dealing with the
ruby the use of this stone as an inlay or onlay that is, an in-
crustation upon jade, both white and green. It is not so much
here a beautiful contrast of colour that is attained, although the
greenish grey, or olive green of the jade, enhances the redness of
the ruby ; but it is a contrast of textures, a contrast of surfaces, a
contrast of translucencies. You see but a little way into the
jade, though it is illuminated by a soft diffused light ; but you see
through the clear deep-toned rubies, with their flashing beams of
crimson.
Now compare with these examples of the artistic employment
of the ruby the ordinary mode in which this stone is set by English
jewellers. Look at the half -hoop ruby ring, with five rubies well
matched in colour, and graduated exactly in size, set close together
in a regular row. You see, perhaps, a little speck of gold appear-
ing here and there at each end of each stone, but nothing is made
of these pieces of gold. You accept them because you know they
RUBIES. 41
are necessary to hold the stones in their places, but you find
neither invention nor beauty in these little bits of gold claws. In
fact, they are frequently prepared by the gross, ready for the
mounting of any stones, provided the shape of the latter be suit-
able. Rubies, sapphires, diamonds, garnets, and emeralds are all
set in the same way, not an attempt being made to adapt the
amount of gold surface or its form to the specific nature of each
gem. But why should not some variety and some appropriate-
ness of mounting be secured for all stones ? How exquisite, and
yet how strong, were the gold and enamel settings of precious
stones in the cinque-cento time in Italy ! Let those patrons who
desire the rather barbaric splendour of masses of rubies gratify
their taste by means of jewels in which the setting is not seen at
all. But surely a fine stone is worthy of a fine and originally
designed setting proportioning the latter in form, in amount
of work and surface, and also in colour, whether red, or green,
or yellow gold, or enamel, to the shape and the hue of the stone
to be set. And even small stones become quite beautiful when
arranged with taste and judgment, in accordance with the con-
ditions just named, and with the further condition as to collocation
of individual stones in accordance with their size and shape. In
pendants, and necklets, and lockets, and brooches there is room for
the expression of some definite and intelligible design. The mere
alternation of rubies with diamonds in rows or chequer work may, in.
some instances, achieve all that is needed. But a design of more
definite form may often be preferable, especially where the stones at
one's disposal are of differing colours and sizes. Then one may con-
struct a suitable bit of leafage or flowerage, duly conventionalised, in
accordance with the nature of the available materials, into forms of
more or less geometrical severity. It should be noted that moon-
stones and white sapphires, in which there often lurks a faint opal-
escence, accord well with rubies ; but it must be kept in mind that
the size of the colourless stones which are to be associated with
42 PRECIOUS STONES.
rubies in such designs as those named is a matter of much moment.
It is a mistake to attempt to match the colourless and the coloured
stones in respect of size, and generally of shape also. One should
be smaller than the other. Large rubies with small moonstones,
or small rubies with large moonstones, and similarly, square
stones with round, and oblong stones with round, generally pro-
duce happier effects than square with square, and oblong with
oblong. Pearls accord with rubies, not only by reason of their
colour relations, but also on account of their shape. In the case
of rubies cut en cabochon, brilliant-cut or square step-cut diamonds
will be found to yield very satisfactory combinations. A border of
small brilliants or roses is a usual and a useful mode of setting off
the qualities of a ruby. The colour of the pale stone is heightened
by contrast with the colourlessness of the diamonds ; the richness
of a rich stone is enriched, and a small stone, if surrounded by
stones still smaller, becomes magnified in proportion.
Next to the ruby, amongst the red stones, comes the spinel or
balas ruby, an entirely different mineral species, without any
pleochroism, and inferior in hardness to the true ruby. The
scarlet, aurora-red, and flame-coloured spinels are the most beauti-
ful , those which verge upon crimson, purple, and violet, looking
dull and black at night, but showing very delicate and often rare
hues by day. Red spinels accord well with small brilliants, or
with larger pearls or moonstones. A fine aurora-red spinel looks
well when surrounded with delicate foliage of white, orange, and
black enamels. Step-cutting, similar to that employed for emeralds,
accords best with the optical qualities of this stone. A biconvex
lenticular form may be so adapted to this stone as to throw a good
daal of soft and rich colour into a specimen which would otherwise
have had little beauty to recommend it. What richness of hue
the finer examples of red spinel may show is to be studied in two
specimens in the Townshend collection, Victoria and Albert
Museum, Nos. 1326 and 1327.
GARNETS. 43
From spinels the passage to garnets is easy.'' But it is not really
difficult to discriminate between the two species, even when the
colours seem the same. If you have a ruby, a spinel, and a garnet
together, the first will scratch the second and the second the third.
The ruby will show two colours in the dichroiscope, the spinel and
the garnet only one. The spinel will exhibit no black bands like
those belonging to the almandine garnet, when viewed with the
spectroscope. And there is a blackness, due to much absorption
of light, in many of the facets of a garnet, as seen from the " table "
of the stone, which will not be observed in the spinel. The garnet,
unless of remarkable size or qualit}^, will hardly be deemed worthy
of being mounted in the same costly way as the ruby or the red
spinel, but it may be said that the same general treatment suits
all these red stones. Yet there are two ways in which garnets
have for long and in many places been treated, to which I may
legitimately refer here. The plates of garnet so largely found in
Anglo-vSaxon and Celtic jewels have remained, in the majority of
cases, intact to the present day. They afford, in their breadths of
soft rich colour, a pleasing contrast to the minute filigree, granulated
and enamel work with which they are generally associated. The
other employment of the red garnet (and it may be traced back to
a far earlier date than that just cited) is as a carbuncle not neces-
sarily foiled at the back. Cut en cabochon, slightly hollowed
behind, and laid on a plain gold surface, the light, as of a glowing
coal, quivers in the midst of a good stone. There is a lovely disc
of antique gold set with five carbuncles in the Gold Ornaments
room at the British Museum. In the centre is a round carbuncle
boss ; then four long pointed arms, much like elongated pears,
radiate from this centre, alternately with a somewhat similar series
of repousse arms, beaten up from the disc of gold, and bordered
with knurled wires onlaid. There is not much work in the piece ;
the intrinsic value of gold and garnets is quite small, but the effect
is delightful ; simple, yet rich ; solid, yet elegant. Can the same
44 PRECIOUS STONES.
praise be honestly given to* modern garnet-work ? Can we feel a
genuine satisfaction either in the design, the execution, or the effect
of a compound big carbuncle of eight lobes, with an eight-rayed
star riveted into the midst of it, the aforesaid star being of hard,
poor, glittering, much alloyed gold, and containing a number of
irregular fragments of defective diamonds ? The star soon gets
loose, and later on the diamonds begin dropping out. But we
will not pursue the history of the piece any further, and will refrain
from calling attention to other obnoxious modes of using carbuncles,
as in a ring with a sham gold knot on either side.
Orange and Yellow Stones. Amongst orange and yellow stones
we may assign the first place to the yellow zircon a stone which is
sometimes found of a hue which may be aptly described as that of
transparent gold. Next to this comes the yellow sapphire, after-
wards the cinnamon stone, or hessonite ; and then we may place the
rich sherry-coloured Brazilian topaz that kind which yields when
heated the finest rose-pink stones. Then the chrysoberyl follows,
and, at some distance, the yellow beryl. Few colour combinations
have been attempted with these yellow stones; puce-coloured spinels
associate with the yellow sapphire very happily, but there are some
enamels which answer equally well. Generally a design of pale
bluish-grey enamel, with minor details wrought in buff and white,
develops the richness of gold-coloured stones. Here mention should
be made of the very rare gem, the spessartite of Ceylon. It is of an
orange-red hue, and is of most fiery brilliance, but is very seldom
met with in commerce. The North American spessartites are
inferior.
Green Stones. There are four green stones about which something
ought to be said the emerald, the tourmaline, the peridot, and the
zircon. Some persons regard the green of the emerald as vulgar.
It is too easy to construct a vulgar, coarse ornament out of emeralds,
even if they be of fine quality. But the_ emerald, step-cut, and
judiciously and quietly mounted, possesses a rich and refreshing
BLUE STONES. 45
colour, just sufficiently dichroic to show passages of bluish-green
with the green. Green tourmalines are much more markedly
dichroic, and it is much to be regretted that, with rare exceptions,
the patrons of the jeweller's art still remain ignorant, not only of the
peculiarly rich and varied qualities of the colour of the tourmaline,
but even of the existence of this gem-stone. With moonstones, or
with grey and ivory-white enamel, long prismatic tourmalines,
carefully cut, afford a delightful colour-combination peculiarly
fitted for larger pieces of personal adornment, such as pendants and
brooches. The so-called green garnets of the Urals, especially those
which are of an olive or pistachio green, are lustrous and fiery stones,
but their softness precludes their use in rings. The same objection
holds good with regard to that lovely stone the peridot ; but this
species occurs frequently of large size, and so is well adapted for
employment in jewels not subject to much attrition. It is a
dichroic stone ; it accords well with small puce, violet, or indigo
spinels, also with black and white enamel ; small dark-coloured
almandine garnets may sometimes be associated with peridots of
fair size advantageously. The most beautiful of all green stones
are those choice green zircons which show a full velvety leaf green.
These always have a low density not exceeding 4- 15, and often no
more than 4. They have the merit of appearing particularly
bright by artificial light. White enamel, or a border of very small
green zircons, enhances their beauty.
The aquamarine and other pale varieties of the beryl are stones
which lose nothing of their brilliancy at night. Their beauty may
generally be greatly enhanced by the judicious use of creamy white
enamel, with delicate arabesques of black or indigo blue. It is not
often that the hue of the beryl is such as to bear the juxtaposition
of other coloured stones.
Blue Stones. Of these there are four that claim notice in this
place sapphire, blue spinel, iolite, and lapis-lazuli. Rich yellow
dead-gold settings suggest themselves for most of these materials.
46 PRECIOUS STONES.
Pearls or diamonds enhance the colour of the paler sorts of sapphire,
spinel, and tourmaline, but afford too striking a contrast with very
richly and deeply tinted stones. A fine indicolite, step or cabochon
cut, accords well with pearls or moonstones arranged as a bordering
or in some conventional form ; the gold work may well receive
an enrichment in the form of grey or olive green enamel. In the
case of the sapphire, the twin beams of diversely-coloured light
which this stone transmits the one azure blue, the other greenish
straw contribute to produce the peculiarly rich quality of its velvety
softness. There is a glittering coldness in all the imitations of the
sapphire the timbre of their colour, to borrow a word from music, is
harsh and unsatisfactory. So a recent imitation, a kind of lime-
spinel made artificially, exhibits apparently the right colour, but it
is flat and uninteresting. To my eye, the difference between a true
sapphire and a false one is the analogue of the difference between
a piece of leafage in wrought iron, and the same piece in cast iron.
As to the arrangement of the sapphire in jewellery, so much depends
upon its depth of colour and its precise hue, that a general rule
would be fallacious. Unless it be pale, when certain green tour-
malines go well with it, the sapphire may be most safely associated
with pearls, diamonds, moonstones, or white topazes, the cutting
and size of the stones being carefully studied.
Violet and Purple Stones. The amethyst, the oriental amethyst,
and the almandine garnet cannot, as a general rule, be safely
associated with stones having strongly marked contrasting hues.
The paler sorts of peridot may, however, be combined with deep-
coloured amethysts or almandines, provided the latter be small in
comparison. The use of opaque fawn-coloured, olive green, and
brown enamel with violet and purple stones sometimes yields
happy effects.
In devising arrangements of coloured stones a mere water-
colour sketch will not suffice. It is always desirable to study with
the aid of the actual materials themselves stones, gold, silver,
ENGRAVED GEMS. 47
enamel the sum of the effects due to lustref texture, form, size,
etc., as well as the balance and distribution of colour.
In any treatment, however cursory, of the topic of this chapter,
the artistic employment of precious stones, some reference ought
to be made to the materials used by the gem-engraver. Nearly
all the minerals employed for intaglios and cameos will be found
mentioned in a subsequent chapter. Most of them are varieties
of silica coloured by small quantities of iron-compounds. Such
are the sards, cornelians, onyxes, chalcedonies, amethysts and
jaspers in which the great majority of antique gems were wrought.
An intaglio well engraved in one of the more transparent or trans-
lucent of these stones, say, on a rich golden of blood-red sard,
shows effects of beautiful colour when viewed by transmitted
light which will be sought for in vain in any faceted specimen.
And then the cameos of later dates, wrought in onyx and sardonyx,
present delightful contrasts of tone and hue in their different
strata, utilised as these layers often were in the building up of a
relief-picture. Of other minerals employed for engraving in
classic times mention may be made of beryl, garnet and plasma ;
the harder and rarer stones were, however, little used until medieval
and later days. It is well to remember that the jacinth, properly
so-called, that is, the orange brown or brownish red zircon, has
never yet been found with an engraving of classic date upon it ;
that the steatite of catalogues of engraved gems is for the most
part serpentine, a harder mineral having an essentially different
constitution ; and that under the conventional term " plasma "
several other minerals are included, such as jade and smaragdite,
both varieties of hornblende, and even the beautiful rich green
variety of serpentine known as antigorite.
CHAPTER V.
ARTIFICIAL FORMATION OF PRECIOUS STONES.
A CLEAR distinction must be made between the imitation of a
precious stone and its actual reproduction or formation by arti-
ficial methods. In the former case we simulate the appearance
of the natural substance by means of some product or prepara-
tion, which may be (and generally is) widely different in chemical
composition and even in many physical properties. In the latter
case we form the very mineral which Nature has formed, endowed
with all its chemical and physical characters, but not necessarily
produced by processes identical with those of Nature. A few
examples of the true reproduction of precious stones will serve to
explain the distinction pointed out with sufficient exactitude.
Take the case of the ruby and sapphire, varieties of crystal-
lized alumina or corundum. If, by the aid of the intense heat of
the oxyhydrogen blowpipe pure alumina, with traces of chromium
oxide or other colouring oxide, be fused, we get a sapphire or ruby
glass, having a hardness and density much less than those belonging
to crystals of alumina. But by prolonging the time of cooling
or by producing the alumina from some of its compounds during
the heating, a portion of the product will crystallise in forms identical
with those of the natural stone, and having the density of 4 and
the hardness 9. For some time the specimens made were small
in size and poor in colour and brilliancy, but the product was
identical with native corundum. Now there have been, among the
large numbers of artificially-prepared rubies, some of several carats in
ARTIFICIAL FORMATION. 49
weight which can be distinguished from the' natural stones only
by a close examination with the microscope. It is then observed
that the artificial rubies contain cavities of a different outline and
nature to those which occur in the rubies made in nature's laboratory.
These cavities are more or less spherical or pear-shaped in the
artificial ruby and their walls are curved ; in the natural stone the
cavities are really negative crystals while their walls are angular.
It was the French chemist Fremy who first made small rubies arti-
ficially, but subsequent workers, by employing larger quantities of
material, modifying the ingredients taken, and allowing the fused
product to cool more slowly, have achieved greater success. The
exact way in which the so-called re-constituted rubies are made
is not known, nor can absolute reliance be placed upon the descrip-
tions which have been given of other methods of ruby-formation.
The red spinel has also been made artificially, of good colour, and in
large crystals. The spinel is a compound of alumina and magnesia,
and by the aid of a substance such as boracic acid, which acts as a
solvent for the constituents of spinel, but which volatilizes at very
high temperatures, crystals of spinel having considerable dimen-
sions, good colours, and the hardness of 8, have been obtained
by several chemists. These stones, having been cut and polished,
could not be distinguished by any test from the natural gems.
Another method of operating, by which rock crystal and a con-
siderable number of hard transparent and beautiful compounds of
silica have been made, consists in causing two substances to act
upon each other when both are in the state of vapour, sometimes
with the aid of the vapour of water as a decomposing agent, and
sometimes without. By the reaction of fluoride of aluminium and
boracic acid, fluoride of boron and alumina are produced, the latter
crystallizing in colourless rhombohedra of white sapphire, or even,
when chromium is added, taking the colours of ruby and blue
sapphire. Similarly treated at a very high temperature in a lime
crucible, the fluorides of aluminium and glucinum have been made
8445. D
5 o PRECIOUS STONES.
to yield distinct crystals of chrysoberyl. It is probable that in
Nature the formation of gem-stones has occurred in the presence of
water, and under very great pressure continued for a long time.
Indeed, it may be concluded that the agency of a very high tempera-
ture has not been generally at work, but that the important elements
in the production of natural crystals have been time, mass, and
pressure.
Chemists have devoted much time and skill to devising methods
for producing diamonds. These methods have rarely been suc-
cessful, but M. Henri Moissan has really made a number of small
very small diamonds by causing carbon to dissolve in molten iron
at the high temperature of the electric furnace and then, by sudden
cooling of the metallic mass, causing the formation of a rigid shell
and so producing great pressure in the interior : the iron mass
treated with acid left a residue containing small diamond crystals :
by slow cooling graphite only was formed.
CHAPTER VI.
IMITATIONS OF PRECIOUS STONES.
THE one point in which all artificial imitations of precious stones
fail is hardness. Practically they all yield to the file, and many
are scratched even by a bit of common glass. Indeed, with rare
exceptions, they consist of flint glass containing an unusually large
proportion of lead and tinctured by the addition of certain colour-
ing oxides, such as cobalt for blue, manganese for violet, as well as
nickel, copper, iron, chromium, or mixtures of these, for other hues.
Colourless s trass, as it is called, commonly contains 38 per cent, of
silica, 53 oxide of lead, 8 potash, and traces of boracic and arsenious
acid, with some alumina and soda. There are three other points in
which these coloured glasses differ from true stones. Besides their
softness already named, they tarnish in impure air, the lead becom-
ing sulphided, and therefore brown ; they are heavier than any of
the stones having specific gravity under 3*3, which they represent,
and they are all destitute of pleochroism. Under the microscope,
or even a hand magnifier, the majority of them show many lines,
and specks, and air-bubbles, which betray their origin and nature
their origin, at a high temperature rapidly reduced ; their nature,
as fused, glassy, non- crystalline masses. The lines and striae are
signs of layers of unequal density and of strain ; the bubbles are
rounded cavities, quite different from those cavities, with angular
and crystalline walls, which some gem-stones, such as amethyst,
beryl, topaz, frequently present. This is true not only of the
many varieties of coloured paste or " strass," which form the usual
8445. J 2
52 PRECIOUS STONES.
materials for imitative gems, but also of the fused compounds
having the precise (or at least analogous) chemical composition
of various gem-stones which have been prepared by Mr. Grsville
Williams and M. Feil. The green beryl glass of the former, and
the blue lime spinel of the latter, afford cases in point.
Instead of substituting a wholly imitative preparation for a
true stone, a doublet or triplet is constructed, in which a colour-
less or pale stone, of no value, is made to appear possessed of a
fine deep colour. The doublet sapphire has a table and crown all
the stone down to the girdle of colourless or pale blue sapphire,
then the lower part of the combination, attached by cement, is
made from blue glass or strass. If then the upper part of the
stone be tested for hardness it answers to that of the sapphire, but
if the base be examined, it immediately betrays its softness. To
avoid this the triplet has been devised. Here we have pale
sapphire for crown and base, but a thin layer of deep blue 'glass
at the girdle a part generally hid by the mount. To detect this
imposture immersion in water generally suffices, for then the three
layers will become visible ; and if a doublet or triplet be boiled in
water, or soaked in a small bottle of chloroform, it usually betrays
its composite nature by falling to pieces. We should add that
some false stones of this sort are coloured by means of a layer of
coloured varnish or cement.
Imitation pearls claim a word of description. They are small
spheres blown on tubes of slightly opalescent glass, and coated
internally with a preparation made from the scales of a certain
fish (as the bleak), and called Essence d'Orient. Into the little
opalescent glass globe a coating of parchment size is introduced,
and then a film of the pearl essence. Lastly, when the essence is
dry, the bead is filled with wax. In order to produce an appearance
like the orient of the true pearl the glass globes before filling are
sometimes heated under pressure with a hydrochloric acid solution ;
in tjiis way an iridescent surface effect is produced.
IMITATIONS. 53
*
Some remarks on the artificial colouring' of natural stones will
be found in chapter vii. ; the different varieties of silica agate,
onyx, cornelian, and even opal are frequently subjected to
processes of heating and saturation with chemical reagents in
order to change their hue or to introduce foreign colouring
matters.
CHAPTER VII.
DESCRIPTION OF PRECIOUS STONES.
DIAMOND.
THERE are three characters which unite to place the diamond in
a unique position amongst precious stones. It is the only gem
which is combustible ; it is the hardest of all minerals ; it
exerts upon light the most energetic refractive and dispersive
power.
The diamond belongs to the cubic or isometric system, and
usually occurs in the form of an octahedron, or in combinations
in which the cube, the dodecahedron, and the tetrahedron
are involved. The faces of these forms are commonly curved :
macled and hemitropic associations of crystals are of frequent
occurrence.
The diamond is easily cleaved in directions parallel to its octahedral
faces. Its fracture is conchoidal. Its hardness is 10.
The lustre both of natural and artificial surfaces of diamond is
peculiarly brilliant, approaching that of such a metal as silver.
This characteristic lustre, which is shared to some extent by sphene,
jargoon and garnet, is known as adamantine it lies between the
metallic and the resinous lustres. The peculiar brilliancy of
diamonds results in part from the total reflection of light from their
internal faces when the incident light strikes them at an angle
DIAMOND. 55
*
greater than 24 13'. Diamond refracts light very strongly the
index of refraction for the yellow ray being 2*419, while that of
rock crystal is but 1*545; of topaz, 1*621; of white sapphire,
i'75; of phenakite, 1*675; and of white zircon, 2. In the
extent to which diamond disperses the several coloured rays
into which white light is split, this gem greatly surpasses all
others. Its " fire," or the flashing of prismatic hues which
characterises this precious stone, is mainly due to this dispersive
power.
The specific gravity of the diamond, when transparent and colour-
less, is of remarkable constancy. When taken in the ordinary way,
without the refinement of certain small corrections which are made
only for scientific purposes, the best results have lain between the
narrow limits of 3 * 52 and 3 ' 53, at 60 Fahrenheit. The fine colour-
less Porter Rhodes diamond has the specific gravity 3*523 : the
smaller but equally fine Gor-do-norr, 3 -527. The former stone was
found at Kimberley, South Africa, on the I2th of February, 1881,
and weighs 474 troy grains : the latter is of Indian origin, and
weighs 213^ grains. The Star of the SoutH, a Brazilian stone of
254! carats, has the specific gravity of 3*529, according to M.
Halphen.
The range of colour of the diamond is extensive ; but various
hues of yellow, grayish yellow, brown, and straw colour, are the
most common. Strongly-coloured diamonds are very rare ; but
green, blue, and even red stones are known. The celebrated
Hope blue diamond, of 44^ carats, and the Brunswick blue diamond,
of 6J carats, are both of the same brilliant and steely blue,
and may very likely have both been parts of the French blue
diamond stolen from the Garde-Meuble, in 1792, and never since
seen.
The least valuable diamonds are those which lack brilliancy, or
have faint hues of gray, brown, and yellow. The most prized are
those which combine brilliancy with decided tints of rose, green, or
56 PRECIOUS STONES.
blue : cinnamon-coloured, salmon, or puce diamonds are also
much esteemed. But pure diamonds, without flaw or tint of any
sort, are those which are regarded as coming up to the market
standard of excellence, and are spoken of as of the " first water."
But even under this designation there is room for considerable
diversity of quality, and consequently of price. And there are
occasionally met with stones of such exceptional purity and beauty
that the ordinary rules of valuation applicable to stones of the
" first water " do not hold good. This observation, of course,
refers to cut stones, that is, to well-proportioned brilliants. Such
a stone, weighing but i carat (3*17 grains), might fetch 30
at a time when a first-water brilliant of the same weight
would not realise above 20. In fact, specimen stones,
like exceptionally large stones, cannot be said to be amen-
able to any precise rule of valuation. The value of the
diamond increases in an increasing ratio with its weight up
to stones of moderate size, beyond which no rule holds
good. Assuming a first-water brilliant of I carat to be worth
20, then an equally fine 2-carat stone would fetch 60, or
30 per carat. Formerly the value of the larger brilliants in-
creased so rapidly with their weight that a stone of 10 carats
was worth over 200 per carat. But since the South African
diamond fields have been extensively worked, large stones have
been found in greater abundance, and have not maintained their
relatively high prices.
In the preceding paragraph brilliants of the first water have
been considered, but it should be added that the diamonds used
in ordinary shop- jewellery, being either dull, flawed, or " off-
colour," possess small market value. Reference may here be
made to a trick by which the yellowish hue of a diamond may be
temporarily masked. The back facets of the stone are lightly
rubbed with a violet-blue wax pencil and the colour distributed by
means of a bit of soft paper. The stone is then returned to its
DIAMOND. 57
*
setting, when it will appear nearly white, the 'blue material correct-
ing the yellow hue of the gem.
For the localities where diamonds have been or are found
reference may be made to the works named in the brief biblio-
graphy in the present manual. The story of the diamond-
fields of the world is full of romantic interest. India, Brazil,
Borneo, and South Africa have all furnished most curious
contributions to the long list of adventures, discoveries, and disasters
connected with the diamond.
Until January 25th. 1905, when the Cullinan diamond weighing
3,032 carats, or 621 J grams, was found in the Premier mine 20 miles
W.N.W. of Pretoria, the largest known diamond was that from the
Jagersfontein mine, Orange River Colony, discovered on June 3oth,
1893. It weighed 971! carats, but owing to an imperfection the
largest brilliant cut from it weighed only 239 carats. It has been
called the " Jubilee " and the " Excelsior," and is of high quality.
The largest diamond found at Kimberley was an octahedron of
503 carats, but this stone was full of black spots. Amongst the
diamonds obtained from the river Vaal diggings the largest is a
rounded pebble weighing 330^ carats, but it is not of good
quality.
It has been estimated that the value of the diamonds added to
the world's stock from the South African mines is more than
85,000,000. Even in one year (1903) the value of diamonds ex-
ported from Cape Colony was close upon 5,500,000. By the side
of these figures the yields in ancient days of India, and, since the
year 1725, of Brazil, do not seem large. At the present time
diamonds are still found in Brazil, while new sources have been dis-
covered in New South Wales, Borneo, and British Guiana. From
the last named colony 173,744 stones were exported in 1902, but
they were very small, for they weighed altogether no more than
11,518 carats.
The winning of diamonds and their mode of occurrence in the
5 8 PRECIOUS STONES.
South African diamond fields are fully discussed in the volume of
Mr. F. Gardner Williams on " The Diamond Mines of South
Africa." Here it must suffice to state that the De Beers' and
Kimberley floors, whither the " blue ground " is conveyed, and where
it is spread out to weather, cover an area of two thousand acres.
Here the blue ground is harrowed, and, if necessary, watered.
After various crushing, washing and screening operations, a material
is obtained in which the diamonds have become concentrated.
This passes at last into a remarkable machine called the Greaser.
The mixture of pebbles, which we may call the concentrate, con-
tains many minerals other than diamonds, such as garnet, ilmenite,
enstatite, chromite, zircon, kyanite, diopside and half-a-dozen
other species, varying in density from 2*6 to 5*3. When this
mixture flows in a current 'of water on to a series of sloping cast-
iron rocking plates covered with a thick layer of grease, the dia-
monds adhere to the grease, while the other minerals, both those
which are heavier and those which are lighter than diamond, are
carried forward and away. Bits of metal and of iron pyrites do
get embedded in the grease along with diamonds, and if any corun-
dum were present it would also remain, but the separation of these
substances from the grease and from the diamonds is quite easy.
The grease loses its adhesive power by becoming superficially
incorporated with minute portions of water, and then needs
remelting and re-spreading on the oscillating " greasers."
This discriminating process is based upon the differing
surface-attractions of certain minerals for water on the
one hand, and for oily and greasy materials on the other.
In simpler words diamonds and a few other minerals such
as sapphires are apparently more easily oiled than wetted,
while the far greater number of minerals are more easily wetted
than oiled.
The following table gives some particulars concerning a few of
the best-known and most important cut diamonds above 100
DIAMOND.
59
carats in weight. The figures quoted are carats, but are probably
not in all instances based upon one exact standard
NAME.
ORIGIN.
WEIGHT
IN THE ROUGH.
WEIGHT
WHEN CUT.
Nizam ....
India
_
277
Excelsior
S. Africa.
97 If
239
De Beers of 1888 .
S. Africa.
428i
228|
Orloff .
India
194f
Darya-i-nur . . .
India . .
186
Victoria ....
S. Africa.
457^
180
Taj-i-mah .
India
146
Regent or Pitt
India
410
136|
Austrian Yellow .
India . ..
1334
Star of the South .
Brazil
2541
125|
Tiffany Yellow * , -,, -
S. Africa.
. .
125|
Stewart ....
S. Africa.
288|
120
Koh-i-nur . '. .
India
W6&
Full discussions of the history of these diamonds and of many
others will be found in the works named in the Bibliographical
Notes. Dr. Max Bauer's " Precious Stones " contains a good
set of figures representing most of the celebrated big diamonds
of the world. A large uncut Cape stone, given to the British
Museum by John Ruskin and named after Bishop Colenso, is
a good octahedron of 129! carats.
Diamonds and the more valuable of precious stones generally
are bought and sold by the weight called a carat. This carat,
whatever its precise value, is always considered as divisible into
4 diamond grains, but the subdivisions of the carat are usually ex-
pressed by the vulgar fractions, one-fourth, one-eighth, one-twelfth,
one-sixteenth, one-twenty-fourth, one-thirty-secondth, and one-
sixty-fourth. The origin of the carat is to be sought in certain
small hard leguminous seeds, which, when once dry, remain con-
stant in weight. The brilliant, glossy, scarlet-and-black seed
of Abms precLitorius constitutes the Indian rati, about 2 grains ;
the Adenantheni pavonina seed is about 4 grains. The seed of
60 PRECIOUS STONES.
the locust-tree, Ceratonia siliquu, weighs on the average 3^ grains,
and constitutes, no doubt, the true origin of the carat.
The carat is not absolutely of the same value in all countries.
Its weight, as used for weighing the diamond and other gem-
stones in different parts of the world, is given, in decimals of a
gram, by the majority of the authorities, as
Madras -2073533
Vienna* .... '20613
Frankfort. . . . '20577
Brazil and Portugal . . '20575
France .... -2055
England .... .'205409
Spain .... -205393
Holland! . '205041
Assuming the gram to correspond to 15*43235 English grains,
an English diamond carat will nearly equal 3*17 grains. It is,
however, spoken of as being equal to 4 grains, the grains meant
being " diamond " grains, and not ordinary troy or avoirdupois
grains. Thus a diamond grain is but '7925 of a true grain. In
an English troy ounce of 480 grains there are 151^ carats ; and
so it will be seen that a carat is not indeed quite 3 * 17 grains, but
something like 3*1683168 grains, or less exactly, 3*168 grains.
Further, if we accept the value in grains of one gram to be, as
stated above, 15*43235, and if there be 151 1 carats in a troy ounce
of 480 grains, it will follow that an English diamond carat is* 205304
of a grarn, not '205409, as commonly affirmed. By recalculat-
ing the value of the diamond carat, as used in different parts of
the world, into its scientific equivalents in the metric system,
the weight to four places of decimals will become, according to
Mr. Lowis D'A. JacksonJ
Turin . . . . . -2135
Persia . -2095
Venice -2071
Austro-Hungary . . . -2061
France '2059
Portugal and Brazil . . -2058
Germany .... -2055
England and British India . -2053
Holland and Russia . . -2051
Turkey -2005
Spain -1999
Java and Borneo . . . '1989
Florence .... -1965
Arabia '1944
Egypt -1917
Bologna -1886
* Schrauf gives '2057. t Schrauf gives -20613.
t Modern Metrology, p. 377.
CORUNDUM. 61
/
On the other hand there would appear to be an arrangement
between the diamond merchants of London, Paris, and Amster-
dam, by which the uniform value for a diamond carat is fixed at
205 of a gram. This value, which was suggested in 1871, by a
syndicate of Parisian jewellers, goldsmiths, and others engaged
in the commerce in precious stones, was subsequently (1877)
confirmed. But, in spite of all efforts to secure uniformity in the
standard by which diamonds are bought and sold, very serious
discrepancies in sets of carat weights as turned out by different
makers still exist.
It may be imagined that the diamond does not lend itself readily
to the art of the gem engraver, still several engraved diamonds
exist. Of these two signets are preserved in the Royal collection
at Windsor. One representing the Prince of Wales plumes was
cut for Charles I. when Prince of Wales, the other and more
important specimen is the armorial signet-ring of Queen Henrietta
Maria. This had found its way into the last Duke of Brunswick's
collection and then became the property of the city of Geneva.
The late Dr. Drury Fortnum bought it and presented it to Queen
Victoria. It was engraved in January 1629 to the order of Charles I.
by one Francis Walwyn, who received the sum of 267 for his
work and for the cost of the boart used. There are other engraved
diamonds, mostly of the seventeenth century, of European work-
manship in various museums and Royal treasuries. But neither
from the artistic nor mineral ogical standpoint are they of much
importance.
CORUNDUM.
Sapphire, Ruby, and Oriental Amethyst.
Next to the diamond in hardness must be placed the many
varieties of the species called corundum. This includes the sapphire,
the ruby, the oriental amethyst, the oriental topaz, and a whol<?
62 PRECIOUS STONES.
crowd of stones, practically identical in composition, but presenting
great diversity in colour and optical properties. All these varieties
belong however to the mineral species corundum, the French
corindon, and consist of crystallised alumina, the oxide of the metal
aluminium. From the mineralogical, or rather from the physical
point of view, the colour of these stones is of no account, while
chemistry has not as yet succeeded in discovering much concerning
the causes of the variations of colour which determine the very
different values set upon different specimens of corundum. That
there are small quantities of magnesia, oxide of iron and silica in
rubies and sapphires of all hue,s, has been ascertained, but this
fact does not furnish the clue to the cause of the blue of the sapphire
or of the red of the ruby. That certain chromium compounds
impart a red hue to certain artificial preparations, both crystallised
and vitreous, of alumina, will not count for much in the absence of
proof that all rubies contain chromium. That iron is the cause of
the dark colour of emery and other impure corundum is, however,
certain : indeed some specimens of emery contain half their weight
of iron oxide.
Coloured corundums, when strongly heated, generally change
their hue, pale blue and pale yellow stones becoming colourless,
and vielet stones retaining only the red constituent of their original
colour. In Ceylon the native dealers frequently offer for sale
specimens exhibiting a beautiful pink or rose colour which is not
natural, but has been produced by " firing " inferior corundums of
the purple variety or oriental amethyst.
Corundum always occurs in crystals or is at least crystalline ;
the forms are six-sided prisms or pyramids belonging to the hexa-
gonal (rhombohedral) system. The lustre is vitreous except on the
basal planes which are often pearly. The six-rayed star seen in
many cloudy sapphires and rubies, especially when cut en cabochon
with the summit of the curved surface lying in the direction of the
principal axis of the prism, is due to the peculiar intimate structure
CORUNDUM. 63
of the crystal. In such a case some of the incident light is reflected
regularly either from the internal surfaces of the layers which make
up the crystal, or of minute cavities or inclusions therein. When
this chatoyant lustre is very marked it gives us the " asterias " or
star-stones known as star-rubies when red and star-sapphires when
blue or grey : the star-sapphire is the ceraunia of Pliny.
Large rough crystals of pale blue sapphire from Ceylon, usually
waterworn, but still retaining their hexagonal form, are employed
for rock drills and for other mechanical appliances and instruments.
Some of these crystals weigh as much as a pound avoirdupois. The
smaller specimens often exhibit one or more zones of blue in planes
perpendicular to the principal axis of the prism, while surface
striations in the same sense are very common. Very rarely true
twins occur, but not infrequently two or more crystals are associated
by interpenetration. Cavities, generally of microscopic size
abound in these large cloudy crystals ; in a few instances, a liquid
with a bubble of gas or vapour may be seen in a cavity of large size.
The cavities have angular walls, and occasionally may be regarded as
" negative " crystals. What is termed the " habit " of corundum-
crystals differs much in the case of specimens occurring in different
localities. For example, while the Ceylon sapphires exhibit a
form prismatically developed a hexagonal bi-pyramid the speci-
mens from the Helena district on the upper reaches of the Missouri
in Montana, U.S.A., are flat crystals in which the basal planes of
the rhombohedron are conspicuous.
The hardness of pure transparent corundums,whatever their colour,
is generally given as 9. In reality, there are differences in hardness
between specimens from different localities and of different hues.
As a rule, the true, rich, red ruby can be slightly scratched by white,
blue and yellow sapphire, yet, on the other hand, if a lapidary be
questioned on this subject of relative hardness he may tell the
inquirer that out of ten corundums from rings which he receives to
restore their lost polish, nine will be sapphires and only one a ruby.
64 PRECIOUS STONES.
The specific gravity of pure, transparent corundum including the
colourless, yellow ; red and blue varieties, is as nearly as possible 4,
the extremes being about 3 97 and 4 05 respectively. A fine yellow
stone without flaws gave 4*006.
All corundums possessing a distinct colour are invariably dichroic.
By this property rubies can be at once discriminated not only from
garnets, but alfo from spinels. The dichroiscope shows, with the
true ruby only, two differently coloured squares. Similarly the
sapphire can be thus distinguished trom the blue spinel, and of
course from blue paste. The twin-colours, polarised in opposite
planes, are these
Sapphire, - cornflower b.ue }
Ruby, t "pigeon's blood "red}
There can be no doubt that part, at least, of the peculiar beauty
of fine rubies and sapphires is due to the play of different hues
caused by their dichroism.
The ruby, when of perfect colour and fair size, is more valuable
than any other precious stone save the emerald. If a diamond of
five carats be worth 350, a faultless ruby of the same weight would
sell for 3000 at least. A very fine stone of a single carat may be
worth as much as 100. All or nearly all the fine rubies met with
in collections are believed to have come from Burma. The district
of Mogok, in Upper Burma, in a mountainous region, includes the
most important ruby-tract. The town of Mogok is itself ninety
miles N.N.E. of Mandalay. Two very fine stones from this locality
reached England in 1875. When recut they weighed 32^ and
39 T 9 ff carats respectively. The rhbies from Siam are, as a rule, not
only too dark in colour, even verging on a brownish red, but they are
also slightly cloudy. A large cut ruby, probably from Burma, was
offered for sale at Christie's auction rooms on May 7, 1896. It
weighed 46! carats ,and was of an oblong form ; its colour was
* frontispiece, Fig. 1. t Frontispiece, Fig. 2,
SAPPHIRE. 65
+
somewhat inclined to purplish red and was not very bright. This
unusually large ruby fetched 8,000, or at least it was knocked down,
or bought in for that sum. It should be added that this stone was
rather clumsily mounted, with four fine large brilliants, as a brooch.
Although Ceylon does not produce many fine or large rubies, a very
beautiful specimen was lately found in the island. It weighed
4j carats, and was at first thought to be an extraordinarily fine
spinel. Its colour is difficult to describe, but perhaps the phrase
" deep dark scarlet " indicates its hue.
Sapphires, that is blue sapphires, are not only more abundant than
rubies, but they are more frequently found of large size. In Siam
and Ceylon occur the chief localities for fine sapphires, but inferior,
or we should perhaps say, less important, specimens are met with in
many parts of the world. An important locality is in the Zamskar
range in Kashmir ; several others have been discovered in the
United States. One of these is a comparatively new locality, some
distance from the original sapphire district in Montana. It now
yields many small sapphires of a uniform and fair blue colour.
These stones have not the rich velvety cornflower blue which
is most esteemed, but they possess the merit of remaining bright and
glittering under artificial light. Now and again, however, a specimen
from the same locality, and of the same blue colour by day, is found
to present a purplish hue at night. In Australia, especially in
Queensland and New South Wales, sapphires occur in several
localities.
Sapphires, even when of the finest blue, do not increase in value
with their size to anything like the same degree as rubies : indeed a
sapphire of perfect hue and tone shows to the greatest advantage
when of quite moderate dimensions ; if very large it may appear
almost black, especially at night. Again large sapphires are far
more common than large rubies. A fine sapphire of i carat is worth
considerably less than a perfect diamond of I carat ; its market
value may be put down as about 10. There are fine large sapphires
8445. E
66 PRECIOUS STONES.
in the possession of Lady Burdett-Coutts, and the Duke of Devon-
shire ; a good rose-cut sapphire may be seen in the Mineral Gallery
of the British Museum, while in the collection of minerals in the
Jardin des Plantes of Paris is the famous Rospoli sapphire weighing
I32 T V carats. The saphir merveilleux, formerly in the Hope collection,
is not a typical specimen, for it is pale in colour and assumes an
amethystine hue at night. Still, in its original form, an octagon fths
of an inch across, and weighing nearly 24 carats, it presented
features of interest. It had once belonged to Egalite, Due d' Orleans ;
it brought 700 guineas when sold at Christie's on May 12, 1886.
Unfortunately it has been since recut.
The sapphire was engraved sometimes in the later Roman days,
but more frequently in the cinque-cento time. The pendent
sapphires in the votive crowns of the Guarrazar treasure (7th
century) in the Cluny Museum, and those on the front of the Pala
d'oro in the church of Sant* Ambrogio at Milan (8th century) are of
Indian origin, perforated and roughly polished, but not faceted.
Small polished sapphires en cabochon are frequently found set in gold
rings of stirrup form, and having a projecting bezel worn by lay
persons as well as by ecclesiastics in the 13 th and I4th centuries.
Amongst the rarer corundums is the pure green sapphire or
oriental emerald. But greenish and greenish blue corundums,
generally pale, as are most of those from Montana, or somewhat in-
clined towards an olive hue, like the majority of the green sapphires
from Ceylon, are by no means uncommon. The true oriental
amethyst or purple sapphire is occasionally met with of a full tone ;
it is an interesting and beautiful stone, strongly dichroic, and often
made up of alternate layers of ruby and sapphire. Violet specimens
of poor quality are generally " fired," so as to change them into pale
rubies. White sapphires of perfect purity do not seem to be com-
mon : a fine specimen of 26 carats is in the author's collection, but
there is not a single good cut example in the Jermyn Street Museum,
the Natural History Museum, or in the Townshend collection.
SPINEL. 67
x-
While the ruby holds its own by candle and gas light, the sapphire
generally becomes dull, often acquiring a somewhat purplish or
amethystine hue.
The white sapphire of modern writers is, in all probability, in-
cluded under the adamas of Pliny ; the blue sapphire is the ancient
hyacinthus ; while the true ruby, the spinel, and certain red garnets
were the several varieties of Pliny's carbunculus, under which name
the writer included several stones which were perfectly distinct
from one another.
In concluding this account of the transparent varieties of corun-
dum mention may be made of the extreme ingenuity with which,
in a pale or poor coloured sapphire, the native lapidary in Ceylon
will take advantage of the presence of a streak or spot of rich colour.
He will so cut the stone as to throw this colour into the entire
SPINEL.
No precious stone includes so wide a range of colours as the
spinel. Following the order of the rainbow, we have red, orange,
green, blue, and violet-coloured spinels ; and also those which
show the hues known as purple, puce, and indigo. Yellow spinels
are not unknown ; some are colourless, others black. Another
character of importance which enchances the position of the spinel
as a gem stone is its hardness, which, though inferior to that of the
ruby, is greater than that of the red garnet. But over against
these excellences of the spinel must be set the lack of fire, due to
its small refractive and dispersive power ; and also the somewhat
prosaic quality of its colour, attributable in part to the absence of
pleochroism. It is perhaps unfortunate for the appreciation of
this species of precious stone that its red varieties seem to enter
into competition with the incomparable splendour of the ruby,
and its blue varieties with the velvety softness of the sapphire.
8445. E 2
68 PRECIOUS STONES.
But the spinel owns other hues which labour under no such disad-
vantages. There is a brilliant aurora red, and a whole suite of
passage hues, between indigo and puce, which stand alone for
curious beauty. And to these may be added steel-grey, slate
and sky-blue, without exhausting the colours offered by the spinel.
The red varieties of the spinel are generally spoken of as " spinel
ruby " and " balas ruby," those designated by the latter name
being inferior in colour and brilliancy, and less like the true ruby ;
but, chemically and physically, there is no sharp distinction between
chem. " Rubicelle " is a term applied to orange and flame -coloured
spinels, those that are violet and purple being called " almandine "
spinels.
Spinels fit for use in jewellery come from many localities. Of
these the chief are in Burma, Siam, and Ceylon ; also in the United
States, in New York, and New Jersey, but the fine large red spinels
come exclusively from India ; several of these, weighing, when
properly cut, as much as 25, 72, 81 carats, have recently found their
way to Europe. One rose-coloured specimen weighed as much as
150 carats, but being too pale was sold for no more than 80. An
unusually large and fine crimson spinel or spinel-ruby, weighing
49 A" cara -ts, from India, proved to have the specific gravity 3*582,
while its index of refraction was for the red ray, 1*711, for the
yellow ray, i 714 and for the blue ray, I 719. Its hardness scarcely
exceeded that of the red garnet, but the tests of specific gravity
and refraction sufficed to show that it was a true spinel. A spinel
ruby of rich colour is seen probably to the best advantage when
step-cut ; the paler hues often look well brilliant-cut. A border
of small diamonds enchances the colour and beauty of a spinel.
The spinel crystallizes in the cubic or monometric system, a
regular octahedron being its most common form. Some of the
natural crystals of spinel are so perfect in shape and polish that
they are quite fit for ornamental mounting without further pre-
paration. The hardness of this gem is 8, while its specific gravity
SPINEL. 69
is about 3*65. The following determinations of the specific gravity
of choice cut specimens of spinel will be useful for reference :
Deep red . . . 3'582
Aurora-red . . .3 590
Puce . . . . 3-592
Sky-blue . . . 3'615
Rose-red . . . 3 '631
Dull purple . . . 3-637
Indigo . . " . . 3-675
Deep indigo . . .3*715
Where the specific gravity of a spinel is too near that of a garnet
to allow of the species being thus distinguished, the superior hard-
ness of the spinel enables the problem to be solved. It is scarcely
necessary to say that the dichroiscope affords no criterion in such
a case, since the spinel and garnet both belong to the monometric
system and are necessarily moriochroic.
Spinel is essentially composed of one molecule of alumina and
one of magnesia, or in 100 parts :
Alumina . . . . 72 j Magnesia . . . .28
But in the coloured varieties decided traces of other oxides occur,
such as those of chromium and iron in the spinel ruby ; oxide of
copper in the grass green spinel called chlorospinel ; and the pro-
toxide of iron in the darker and opaque varieties. Some speci-
mens of pleonaste, the black spinel of Ceylon, have been found to
contain over 20 per cent, of ferrous oxide, the protoxide of iron,
which takes the place of its equivalent of magnesia.
Spinels in true crystals and very hard have been formed artifi-
cially, though not of fine quality and large size, by several different
processes, such as heating alumina, magnesia, and boracic acid
together to a very high temperature. The vapour of aluminium
chloride passed over heated magnesia also produces spinel crystals,
so does the strong heating together of magnesia and alumina.
Some imitation blue spinels or sapphires have been made by the
fusion together of alumina, lime, and a little cobalt. These in-
gredients have, however, given a blue glassy mass softer than true
spinel, and merely enclosing here and there a few minute crystals
of what may be termed a "lime spinel," the main mass being
7 o PRECIOUS STONES.
indeed the same substance, but in a vitreous or non-crystalline
state. The specific gravity of this lime spinel, which has been
sold for blue sapphire, is lower than that of sapphire or even than
that of blue spinel.
TURQUOISE.
The turquoise acquired its name from having been imported
into Western Europe by way of Turkey. The best specimens
come from the district of Nishapur, in the Persian province of Khor-
assan, where the gem occurs in a porphyritic rock. The hardness
of the stone is nearly 6, and its specific gravity 2*75. There is a
peculiar quality in the colour of the best turquoises, which is partly
dependent upon the delicate hue of its blue, with which a slight
infusion of green is mingled, and partly upon the faint translucency
of the stone. For turquoise is indeed not opaque, thin splinters
transmitting light easily.
It is very probable that turquoise was described by Pliny under
the three names of callais, callaina, and callaica. Turquoise
is often now called callaite, while an allied mineral from a Celtic
grave near Mane-er H'roek in Lockmariaquer, and now preserved
in the Museum of the Polymathic Society of Morbihan, has been
called callais and callainite, but has lately been proved identical
with the variscite of Breithaupt, a mineral described in 1837.
The true turquoise, which shows various hues and tones of blue,
greenish blue, and bluish green, is not to be confounded with the
blue fossil turquoise, or odontolite, which is in fact fossil ivory,
generally of Mastodon teeth. The true turquoise owes its colour
to phosphate of copper, and its powder becomes dark blue when
moistened with strong ammonia. Odontolite is coloured by
phosphate of iron, is more opaque and heavier than turquoise, and
much softer, and shows its bony structure under the microscope,
Turquoise often becomes green by age ; this change is frequently
noticeable in the turquoise cameos of the Italian cinque-cento.
CALLAINITE. 71
*
Turquoise is a phosphate and hydrate of alumina, associated
with a hydrated phosphate of copper ; it always contains small
quantities of phosphate of iron and manganese. A fine Persian
specimen contained in 100 parts :
Phosphorus pentoxide 32'8 I Water .... 19'3
Alumina , 40'2 | Copper oxide . . . 5'3
Iron and manganese oxides . . . 2*5
Turquoises of considerable size and occasionally of good colour
are met with having Persian and Arabic inscriptions or ornamental
designs engraved upon them. The hollows of the designs are
sometimes gilt, sometimes inlaid with gold wires.
The distinction between turquoises de la vieille roche and those
de la nouvelle roche has a real existence. The former, chiefly
obtained from the Nishapur district, are superior in quality of
colour, even when the latter belong to the same species, and are
not, as is often the case, identical with odontolite, or bone tur-
quoise, or with variscite.
The turquoises from New Mexico vary much in colour ; and
if originally of a fine blue do not invariably preserve their hue.
Some of them contain interspersed particles of quartz. No less
than 7 per cent, of copper oxide occurs in some of the stones from
the Burro Mounts, Grant County.
CALLAINITE.
There are three minerals passing under the name of turquoise.
The true turquoise is the callaite of mineralogists ; then there is a
fossil turquoise or odontolite ; and lastly we have a pale bluish-
green stone which has been described under the names callais,
variscite, and callainite, and which presents a near relationship to
the true turquoise. Its hardness is 4 ; its specific gravity 2.55 ;
and its percentage composition :
Alumina . . . . 32'4 | Phosphorus pentoxide . 44 '9
Water . . , 22 ?
There is another blue mineral related chemically to turquoise
72 PRECIOUS STONES.
and callainite and known as lazulite. It is essentially a hydrated
phosphate, but contains besides aluminium, a considerable pro-
portion of magnesium and iron ; copper is generally absent.
It is softer and rather heavier than turquoise, and is far more
difficult to dissolve in acids than that species. In colour it varies
from a fine sky-blue to a tint not far removed from that of pale
lapis-lazuli a perfectly distinct mineral. Lazulite was occasionally
used in ancient times as an inlay, for instance in the gold armlet
from the Oxus now preserved in the British Museum.
TOPAZ.
Although the topaz is a perfectly definite and distinct mineral
species, yet three .different stones are commonly called by this
name. But the topaz known as " oriental topaz " is in reality
the yellow sapphire, a kind of corundum ; the occidental or Scotch
topaz is nothing but yellow quartz ; while the true topaz, some-
times spoken of as the Brazilian topaz, is the only one which in
reality may properly bear the name. The hardness and specific
gravity of these three stones are very different, and furnish good
criteria for their discrimination :
Hardness. Specific Gravity.
Oriental topaz .... 9 4*01
Brazilian ,, 8 3 '53
Scotch ,, .... 7 2-65
The true topaz belongs to the orthorhombic system ; its crystals
are prisms, usually having but one end regularly terminated.
The cleavage of topaz is highly perfect and basal, that is, trans-
verse to the length of the prism. The prismatic faces are commonly
deeply channelled but brilliant. The refractive indices of topaz,
in the three directions of the axes, are, for the yellow ray in a
colourless crystal :
a = 1-622; ft = 1*615; 7 = 1*612.
The double refraction of topaz is strong, and the pleochroism
of coloured specimens very marked. A wine-yellow crystal from
TOPAZ. 73
Brazil showed two images, one rose pink arkf the other brownish
yellow, in the dichroiscope ; after heating, the same crystal gave
a stronger pink colour and a dull white. The colours of topaz
are many and beautiful ; the rose pink (often called burnt topaz)
is commonly obtained by heating the richly coloured wine-yellow
or amber-yellow crystals, but occasionally occurs in natural speci-
mens. Blue and pale-green topazes are sometimes found of large
size, and are more brilliant than similarly tinted beryls. Colour-
less topazes vary a good deal in purity of hue and fire ; those
from Brazil are often of remarkable whiteness, and show dazzling
reflections of pure white light when properly cut. The polish
which the topaz takes is very high, and the surface of cut specimens
is exceedingly smooth and slippery to the touch.
The specific gravity of the topaz, even in perfectly flawless and
transparent specimens, ranges between rather wide limits, so far
as the colourless specimens from different localities are concerned.
The coloured specimens show a much smaller variation.
Topaz, white . . . 3 -597
. . . 3-595
. . . 3-585
. 3-572
Topaz, rose pink . . 3 '534
. 3-533
,, sherry yellow . 3 '539
blue 3-541
The topaz is one of the few precious stones containing the element
fluorine ; it may be regarded as a silicate of alumina, in which
part of the oxygen of the silica is replaced by fluorine. The analysis
of topazes from different localities points to a composition which
may be represented in 100 parts by these figures :
Silicon . . . . 15-5 I Oxygen .... 36 '8
Aluminium . . . 30'2 I Fluorine . . . . 17 '5
A little water is always present in topaz ; it is probable that the
hydroxyl of this replaces a part of the fluorine. Such replacement
helps to account for slight differences in the physical characters of
topaz from different localities. When strongly heated, topaz not
only changes in colour, but loses considerably in weight ; hydro-
fluoric acid, fluoride of silicon, and fluoride of aluminium being
74 PRECIOUS STONES.
given off to the extent of 20 to 24 per cent. With moderate heating
no loss of weight, but merely change of colour, occurs, the bulk
of the stone remaining unaltered, and consequently its specific
gravity suffering no increase or diminution. The sherry-coloured,
the brown, and the other tinted topazes, which are susceptible of
being " pinked " by heat, exhibit a very curious phenomenon
during the operation. When a suitable stone is packed in magnesia
or other inert material, and heated in a crucible, the specimen, if
removed before it is cold and laid upon a white surface, shows
scarcely any trace of colour ; but after a little time, when the stone
has acquired the temperature of the air, the desired pink hue
makes its appearance. If the temperature reached has not been
sufficiently high, a salmon tint, or a hue like that of a drop of
blood mingled with much water, is obtained instead of a rose-petal
pink. What the cause of these changes of colour is remains doubt-
ful : it may be a change in the molecular or physical condition of
some minute trace of a coloured constituent in the topaz, or it may
be an actual chemical change. Anyhow the colour of topaz is a
very unstable one, for light, or at least the solar rays, soon exerts
a bleaching effect on many pale-coloured specimens ; so that the
fine suite of wine-hued Russian crystals, collected by Colonel de
Kokscharow, and now in the British (Natural History) Museum,
is kept shrouded from the light of day.
Topaz occurs in several Scotch and Irish, and in some English,
localities St. Michael's Mount in Cornwall, may be named amongst
the latter. Villa Rica, Minas Novas in Minas Geraes in Brazil,
Flinders Island, and many places in the United States, as well as
several Siberian localities, furnish splendid specimens of colour-
less and coloured topaz. The white topazes from Flinders Island
are less brilliant than those from Brazil. Good topazes come
from Pegu and Ceylon, and they have been found in Australasia.
A magnificent deep blue topaz was found in Ceylon in 1899 : when
cut, it weighed no less than 355 carats. The topazios of the
TOURMALINE. 75
ancients was our chrysolite and peridot, -'not the stone now
called topaz, which was not known as a distinct stone until com-
paratively modern times. The topas (pitdah) of Aaron's breast-
plate was probably a peridot.
The commercial value of the topaz is small and variable.
Very richly -coloured specimen stones, suitable for pendants
may be bought for a pound or a few pounds ; they are often sold
by the ounce, not by the carat.
TOURMALINE.
The tourmaline is marked out from all other precious stones
by a very complex chemical constitution, and by a very interesting
optical structure. Its hardness, 7*3 to 7*5? suffices to protect it
from wear, while the range and quality of the colours which it
exhibits commend it to those persons who appreciate the artistic
value of jewellery in which other stones besides those which are
well known and popular form dominant elements.
All the minerals called by the names " indicolite " (blue),
" rubellite " (red), " schorl " (black), and " achroite " (colourless)
form but one species tourmaline. These differences of colour
are accompanied by differences of composition, so that we have a
series of varieties of tourmaline, in which, while the proportion
of silica is fairly constant, the bases consist of the oxides of iron,
magnesium, sodium, manganese, and aluminium in differing pro-
portions. Water is also present, and sometimes lithia and potash.
To give some notion of the chemical complexity of the tourmaline
we may cite an analysis by Rammelsberg of a green Brazilian stone
of specific gravity 3*107 :
In 100 parts:.
. 2-37
-.. 1'20
. -37
' . 7-21
2-09
In 100 parts.
Silica
. 38-55
Lime
Alumina .
. 38-40
Soda
Manganic oxide
. . -81
Lithia .
Ferric
. 5-13
Potash .
Ferrous ,,
. 2-00
Boron trioxide
Magnesia
73 Fluorine.
76 PRECIOUS STONES.
The specific gravity of tourmalines varies between 3 and 3.25.
The following determinations were made with particular care :
Tourmaline, almandine coloured . . . 3 '009
rich rose pink .... 3 '044
orange-brown, from Ceylon . . 3*082
lemon yellow . . . .3'106
green, from Brazil . . . 3 '109
black, Bovey Tracey, Devon . 3 -120
green, from Brazil . . .3*154
The tourmaline occurs crystallised in the form of prisms belonging
to the rhombohedral system ; some of the faces are striated or
even channelled. The hardness of perfectly flawless transparent
tourmalines is from 7-3 up to 7*5.
The optical properties of tourmaline are most striking. When
a crystal is viewed along the direction of its principal axis, it is less
transparent and of a different colour than when viewed across that
axis. The coloured varieties, or most of them, absorb and quench
to different degrees the ordinary ray, which is polarised in a plane
parallel to the axis, while they allow the extraordinary ray,
polarized in a plane perpendicular to this line, to pass. Examples
of the marked dichroism, which is so conspicuous a feature in the
majority of coloured tourmalines, may be seen in this list of twin
colours of the two polarized rays passing along and across the
crystal respectively :
ORDINARY RAY.
Yellow brown.
Deep violet brown.
Purple.
EXTRAORDINARY RAY.
Asparagus green.
Greenish blue.
Blue.
The following are some additional instances of the twin colours
seen in tourmalines, owing to the optical peculiarity just named.
These examples were observed with the aid of the dichroiscope,
which serves for the study of such a phenomenon admirably, causing,
as it does, a complete separation of the oppositely-polarized and
TOURMALINE. 77
*
differently-coloured rays, not attainable by mere inspection of a
polished slice of a tourmaline crystal :
COLOUR OF STONK.
TWIN COLOURS.
Red
Brownish red ....
Brown .......
Green ......
Salmon Rose pink.
Columbine red Umber brown.
Orange brown Greenish yellow.
Pistachio green Bluish green.
A few illustrations of the influence of this powerful dichroism
upon the appearance of cut and faceted tourmalines will be of
service, not merely in identifying doubtful specimens, but in ex-
plaining the peculiar and exquisite quality of the colours which
this gem-stone shows. If we cut a green tourmaline in such a
manner that the table and culet are perpendicular to the axis of
the crystal, the probability is that the gem will appear, especially
in its thicker parts, perfectly opaque and black. Held sideways
we may see some greenish and olive green hues, by looking across
the stone from one part of the girdle to another. Now the same
green tourmaline may be so cut as to present a brilliant appearance,
with a fine play and interchange of two hues of green, by making
the table parallel with the axis. If the crystal be a yellowish brown
one, a very beautiful effect is secured by cutting it in the form
of a brilliant, but with a small table parallel with the axis. The
templets and other facets of the crown should be well developed
so as to display, as the stone is viewed in different positions, the
different colours of the light transmitted and reflected in different
directions which become visible in one after another of the facets.
If one of these be at one moment greenish yellow, presently it is
yellowish brown, and then russet.* With pale yellowish and
greenish grey tourmalines cut in a similar manner, there will be
seen other and equally striking changes of hue.
* Frontispiece, Figs. 6 and 8.
7 8 PRECIOUS STONES.
In the table on page 76 several localities of tourmaline are given.
Of these some yield crystals, which are parti-coloured, perhaps
having a rosy central position enclosed in a green shell. Recently
many fine tourmalines have reached this country from Heemskirk
Island, Tasmania. Some of the green crystals from this locality
are large and clear : tourmalines of peacock-blue and apricot-
yellow have also been found. The Heemskirk green crystals are
well suited for polariscope purposes.
When a tourmaline is rubbed, or, better still, when it is heated,
it becomes electrically charged. The polarity of the charge is
beautifully shown when a mixture of red lead and sulphur in powder
is allowed to fall from a muslin sieve upon a tourmaline crystal
when in process of cooling. The red lead will gather about the
negatively electrified end, the sulphur about that which is positively
electrified.
GARNET.
The great group of the garnets includes several gem-stones which
would not be included under a single name, as having many char-
acters in common, were it not that chemical and crystallographic
properties must be allowed to overbalance the more obvious
peculiarities of these minerals. Garnets present almost all hues
and tones of colour save those in which blue predominates, while
they vary greatly in hardness and specific gravity. But the crystal-
line forms in which they occur are all referable to this same system,
the cubic or monometric, while the chemical expression which re-
presents their constitution is identical in structure, though one
or another constituent be replaced by analogous elements. All
garnets are normally singly refractive and monochroic ; where
double refraction is observed it is due to internal stresses. The
following list includes the chief varieties of garnet :
1. Cinnamon-stone or Hessonite Calcium aluminium garnet.
2. Almandine and Carbuncle Ferrous aluminium garnet.
GARNET. 79
'5. Pyrope or Bohemian garnet Ferrous inagnesi(fm calcium aluminium
garnet.
4. Spessartite or Manganese garnet Manganous aluminium garnet.
5. Rhodolite Ferrous magnesium aluminium garnet.
6. Demantoid or Bobrovka garnet Calcium ferric garnet.
7. Uvarovite Calcium chromium garnet.
Besides the bases indicated in the above list as characteristic
of the several kinds of garnet there are in all of them minor con-
stituents as to which a few words are required. Amongst these
special mention must be made of chromium sesquioxide to which
the emerald hue of some demantoid has been attributed and which
is also found in much pyrope. Traces of other oxides likewise
occur in several of the remaining varieties. So also in those
garnets in which iron is a large and essential constituent, this
metal is found to exist, at least generally, in two states of oxidation
indicated by the terms ferrous for the protoxide and ferric for
the sesquioxide. Thus, almandine, along with 32 or 33 per cent,
of ferrous oxide, generally contains 2 or 3 per cent, of ferric oxide,
while in demantoid a little ferrous oxide is associated with about
30 per cent, of ferric oxide. Then, too, manganous oxide, which
is the chief protoxide in spessartite, occurs in small proportion in
all or nearly all the remaining varieties of garnet. These and other
minor peculiarities of composition are all covered by the chemical
expression of " garnet formula." This formula contains three
molecules of silica (Si0 2 ) combined with cne molecule of a sesquioxide
such as Fe 3 3 , A1 2 O 3 or Cr 2 Og and with three molecules of a mon-
oxide, such as FeO, MnO, CaO or MgO. If any of the above
sesquioxides be represented by the formula R. 2 O 3 and the above
monoxides by MO, then the general expression for garnet becomes
R 2 3 , 3MO, 3SiO 2 . One character common to all garnets save
uvarovite is their fusibility before the blow pipe ; they thus yield
a vitreous mass which is of much lower density than that of the
original garnet before fusion. As the members of the garnet
group differ so widely from each other in appearance, hardness,
8o PRECIOUS STONES.
specific gravity, etc., it will be advisable to discuss the several
varieties used in jewellery separately.
1. Cinnamon stone or Hessonite. This garnet (generally but
incorrectly called essonite) has long been confused with zircon
of similar colour a sort of deep golden hue with a tinge of flame
red. All the engraved gems said to be of hyacinth and jacinth
that is, zircon are in fact cinnamon stones, or, as they may be
called, hyacinthine garnets, not zircons ; we except those which,
while resembling cinnamon stone, are only sard. The three species
may be discriminate^ in several ways, the true hyacinthine zircon
having, for example, the specific gravity of 4 '6, the cinnamon
stone 3 '7, and the sard, 2 '66: other criteria are furnished by
differences in lustre, harness and refractivity. The best hessonites
9 I
come from Ceylon : they may be recognised, by their peculiar
appearance, in a good light, when examine & by the aid of a hand
magnifier. This appearance is that of a finely granulated texture,
as if made up of san^ grains barely molten together. The specific
gravity of cinnamon stone will be seen, from the following deter-
minations, to be fairly constant : (i) 3*69. (2) 3*657. (3) 3*642.
(4) 3*642. (5) 3 '666. Grossularite belongs here.
A cinnamon stone from Ceylon gave on analysis these per-
centages :
Silica . . . . 40-0 Iron oxides . . . 3 '4
Alumina .... 23'0 Manganous oxide . . 0'6
Lime . . . .30*6 Other substances . . 2'4
Antique Roman intaglios on cinnamon stone, both light and dark
in tone, are numerous ; cameos are not infrequent. This stone
is more easily cut and engraved than the full red varieties of garnet,
having indeed a degree of hardness very near that of quartz,
instead of quite half a degree above it.
2. Almandine, carbuncle, precious garnet. The range of colour
in this variety of garnet lies between a violet or purple near that
of the amethyst and a brownish red or reddish brown. The pure
GARNET. 81
+
fiery scarlet specimens, the deep red, and the crimson are com-
monly cut en cabochon, with a hollow at the back to receive a bit
of foil ; such stones are called carbuncles. A delicate silvery
cross is seen in some carbuncles, which may be called star
carbuncles ; this star has but four rays instead of the six belonging
to the star sapphire. The garnets of this variety generally show
a very distinctive set of three black bands when viewed with the
spectroscope.* This peculiarity was discovered by the present writer
and published in the " Intellectual Observer " of 1866. This group
of absorption bands may be made to serve as a criterion for dis-
criminating between the red garnets of this variety and red spinels.
When a red garnet is faceted the table should not be large nor the
stone be left very thick or a blackish appearance will result. The
almandine is said to have arisen from Pliny's adjective alabandicus,
applied to the carbunculus cut and polished in the town of Alabanda,
in Asia Minor. Syriam, once the capital of the ancient kingdom
of Pegu, was, it appears, an important mart for fine almandines,
hence the term 'Syriam or Syrian garnets was applied to the choicer
specimens of almandine. Besides the old and numerous Indian
localities of almandine, Brazil, South Australia and German East
Africa furnish fine specimens.
Transparent red garnets of very large size have been fashioned
into cups and boxes. Slabs of polished garnet, sometimes of con-
siderable area, were employed as inlays in Celtic and Anglo-Saxon x
jewellery.
The red or precious garnets of the variety under discussion are
never found with the exact theoretical composition of a pure " ferrous
aluminium " garnet ; there is always some admixture or replace-
ment. But a characteristic specimen was found to contain, in
100 parts, about
Silica . ... 39
Alumina . . . .19
Iron oxides . . - . .37
Manganous oxide . . 1
Magnesia . . . . 2
Lime . 1
Frontispiece, Fig. 10.
82 PRECIOUS STONES.
Nearly all the iron was in the form of ferrous oxide. The hard-
ness of this variety of garnet is about 7 '5, while its specific gravity
is seldom less than 4 i and may be as high as 4 3
3. Pyrope or Bohemian Garnet. The Pyrope is essentially a
magnesium iron aluminium garnet, but variable, and sometimes not
inconsiderable, quantities of other metals are present, so that this
variety of garnet must be regarded as belonging to a mixed type.
Its colour is usually blood-red, or deep red with some orange. It
is usually perfectly flawless and transparent, and, when of any size
may appear of so dark a colour as to be almost black. It is this
blackness which is the chief distinguishing feature between a blood-
red pyrope and a blood-red ruby, though the superior lustre, fire
and dichroism of the latter gem afford other criteria in the dis-
crimination of the two stones. Moreover, in hardness and in specific
gravity the pyrope is inferior to the ruby. This stone, which is
found in great abundance, though of small size, in many places in
Bohemia, is usually rose-cut and often foiled. Specimens from other
localities, such as those from South Africa (often wrongly called Cape
rubies) are not infrequently brilliant-cut. The hardness of pyrope
lies between 7J and 7J ; its density is just below 3*8, on the average
about 3*75. It is less easily fused than any other garnet save
uvarovite.
Three analyses of pyrope are here given, as it is well to have this
means of comparing the percentage composition of this garnet
from different localities, and its divergence from almandine :
BOHEMIA. NEW MEXICO. S. AFRICA.
Silica ....
41-4
42-1
4TO
Alumina
22-3
193
22-0
Ferrous oxide
. ' 9-0
14-0
13-5
Ferric oxide .
. 1-0
1-0
1-6
Manganous oxide .
2-0
0-4
0*5
Chromium sesquioxide .
3-5
2-6
1-5
Magnesia
15-0
14-0
15-0
Lime
47
5-2
5-0
These analyses cannot be discussed here, but this at }eat may
GA RNET. 83
+
be said concerning them, that they do not accord exactly with the
garnet formula, and that the state of oxidation of the three metals,
iron, manganese and chromium has not been ascertained with
complete accuracy.
Pyrope is well known through the roughly faceted beads cut
from this garnet and through the cheap Bohemian jewellery where
it figures as the chief stone. Choice specimens are worthy of better
cutting and better settings.
4. Spessartite or Manganese Garnet. As a rule this variety of
garnet does not occur in a sufficiently clear state to allow of gem-
stones being cut from it. Some considerable quantities, however
from Amelia Court House, Virginia, U.S.A., have been cut and
polished. Some of the very small aurora-red spessartites from
Nevada have yielded brilliant gems, but, at present, the very finest
specimens, extremely lustrous and of a magnificent aurora-red or
flame-colour, are found in one or two localities in Ceylon. These
resemble cinnamon stone and have been sold as very choice speci-
mens of that kind of garnet, but they are incomparably more beau-
tiful. They are easily distinguished from hessonite by their higher
specific gravity which is 4*14, instead of 3*66. A step-cut spes-
sartite from Ceylon in the author's possession weighs 6| carats,
having lost 2 carats by re-cutting in London, but with a most
marked improvement in the appearance of the gem. Very few of
these stones have been found ; they bring 2. or 3. per carat when
of fair size, that is above 2 or 3 carats in weight.
5. Rhodolite. This beautiful variety of garnet is of a rose-red
colour somewhat verging on purple. It is more brilliant and less
deep in tone than almandine and pyrope, while it partakes of the
chemical constitution of both of these stones. It shows, though
somewhat faintly, the system of black absorption-bands which
is characteristic of almandine. Its specific gravity is 3 . 84, a figure
much nearer that of pyrope than that of almandine. Rhodolite
occurs at Cowie's Creek and Mason's Branch in Macon County,
8445, F 2
84 PRECIOUS STONES.
N. Carolina, U.S.A. It is quarried and cut to a large extent as a
gems tone.
6. Demantoid or Bobrovka Garnet. This is a calcium ferric
garnet from the Syssersk district on the Western slopes of the
Urals. It is softer than any other garnet, but its colour that of
a rather yellowish green emerald has made it a valuable and
popular stone. Unfortunately dealers and jewellers have given
it names to which it has no right. It was called " Uralian emerald "
at one time, and now it is generally called olivine, the proper desig-
nation of an entirely different stone, namely, the peridot. De-
mantoid is in reality only one of a number of sub-varieties, having a
wide range of colours and of constituents, of calcium ferric garnet,
but it is the only one that is appreciated as a precious stone. The
most esteemed colour is near that of the emerald, but the yellowish,
green, the pistachio, asparagus and olive-green stones, as well as the
Jiver -coloured stones, are not without beauty, owing, doubtless, to
the lustre of the polished facets of the gem, and to its high refractive
and dispersive powers, which impart to it a brilliancy and fire
possessed by no other green stone. Demantoid appears to advan-
tage under artificial illumination. Its hardness is about 6 rather
too low for a ring-stone. The specific gravity of three specimens
proved to be as follows :
Green- yellow, 3*854; Pistachio-green, 3*848; Emerald green,
3-849. Although demantoid has been frequently analysed its con-
stitution has not been brought precisely into line with the garnet
formula. It is thought that the emerald green specimens owe their
distinctive hue in part to the presence of chromium.
7. Uvarovite, or Calcium Chromium Garnet. This variety
always contains some alumina in place of pr.rt of the chromium
sesquioxide. It is of a fine emerald green, has the hardness 75
and the density 5*5, but it rarely admits of being cut as a gem
owing to its occurrence in very small crystals, or its want of com-
plete transparency. Of other garnets mention may be made of
PERIDOT. 85
*
black garnets used in the i8th century in mourning jewellery ; of
the yellow and greenish-yellow garnets known as topazolite, and of
colophonite which resembles common rosin : all these are essen-
tially calcium ferric garnet, and with demantoid are included
under andradite.
PERIDOT.
Under the species olivine are now included both the yellow
and greenish- yellow chrysolite and the pistachio green or leek
green peridot, or evening emerald. The latter possesses a quieter
hue than the emerald, and needs to be in rather large pieces that
its colour may be properly developed. Perhaps the peculiar hue
of the peridot may be best suggested by that seen on looking
through a delicate green leaf. It contains more yellow and grey
than the emerald. The peridot is dichroic, giving a straw yellow
and a green image.* It crystallizes in the orthorhontbic system.
Its hardness is unfortunately rather low, about 6*5, so that polished
specimens are easily scratched by wear. The peridot is, however,
well suited for engraving, and forms, when set in black and white,
or orange enamel and gold, a beautiful stone for pendants. En-
graved peridots are, however, with very few exceptions, of modern
date. The specific gravity of the peridot is not changed by heat.
A careful determination of the specific gravity of a fine rich-
coloured peridot gave 3*389. A range of 3*35 to 3*44 is usually
assigned to this variety of the " precious olivine."
Fine peridots come from Egypt, but most of the large specimens
now met with are derived from old ecclesiastical and other orna-
ments. But during recent years at least one Egyptian locality
has been discovered or re-discovered. One of the peculiarities
of olivine is its occurrence in meteorites. There are some good
peridots in the Townshend collection, and characteristic specimens
in the British Museum and in the Museum of Practical Geology.
* Fig. 4. Frontispiece.
86 PRECIOUS STONES.
The percentage composition of peridot, though the ferrous
oxide may be more or less replaced by magnesia, is approximately :
Silica . . . . . 41 | Ferrous oxide . . . 9
Magnesia . . .50
Manganese, nickel, and lime have been found in small quantities
in some oli vines.
The term olivine is now wrongly applied by dealers in precious
stones and by jewellers to the green garnets or demantoid from
Bobrovka ; these, for a time at least, were called, with equal in-
correctness, Uralian emeralds. A considerable quantity of pale
green cut gemstones has been sold in London as peridot, but on
examination proved not to be that variety of chrysolite. They
were softer than peridot, and, though more glittering in lustre,
were of poqrer colour. They were not dichroic and showed no
sign of crystalline structure. On analysis they were found to
contain much more silica and much less magnesia than peridot,
while alumina and soda were present in distinct quantities ; if the
material had not been known to be a natural product, these speci-
mens would have been called green glass. Their composition
varies widely, and so does their density, the latter ranging from
2*36 to 2*63. The mineral which occurs in several Bohemian and
Moravian localities is known as water-chrysolite, psendo chrysolite,
moldavite and bouteillenstein. Various opinions are held as to
its origin, some mineralogists even going so far as to state it to
be an artificial glass from the site of early glass factories. It has
also been conjectured that it may be of meteoric origin. Some
glass has undoubtedly been sold as moldavite, but the genuine
material differs in intimate structure, in fusing point and in
chemical composition from any kind of glass. It is not identical
with obsidian, while its occasional occurrence as rolled pebbles
in the gem-gravels of Ceylon strengthens the view that there is
a moldavite which is a natural product.
BERYL. 87
*
BERYL.
(EMERALD, AQUAMARINE.)
The emerald and the aquamarine are included by mineralogists
under the species beryl. The differences of colour are due to
minute traces of compounds too small to be determined with
exactitude. The chemical constitution and the crystalline form
of all the varieties of the mineral are the same. The form is a
regular six-sided prism, belonging to the hexagonal (rhombohedral)
system. This prism is often striated, both internally and ex-
ternally, with delicate lines and fissures which are invariably
parallel with its sides, not, as is the case with quartz crystal, at
right angles with or across these sides.
The specific gravity of the different varieties of beryl, when
free from flaws, cavities, and intruding minerals, is as nearly as
possible 2*7. So the emerald and the aquamarine are a little
heavier than rock crystal (2*66) and much lighter than green
garnets (3*85) or green sapphires (4). Here are a few determina-
tions of specific gravity made with stones of different colours :
Blue beryl . . . . 2701
Yellow beryl. r . . 2 -697
Emerald (from Muzo) . 2 '710
2-704
Aquamarine (Brazil) . 2-702
Brown yellow beryl . .2'
The hardness of beryl varies between 7*5 and 8, the fine
emeralds of Muzo being less hard than the aquamarines of Brazil
and Siberia ; they are also rather brittle. The indices of refraction
for the green ray are in the emerald of Muzo :
w = 1-584; = 1-578.
The dichroism of some forms of beryl is very strong ; tnis is
particularly the case with the emerald. Viewed across the prism
with the dichroiscope the two images of the emerald are seen to
be of different hues of green one verging on yellowish green,
and the other being a green with a tinge of blue.* The same
* Fig. 3. Frontispiece.
88 PRECIOUS STONES.
e^ec-t of hue may be noticed in small parcels of cut emeralds
cut, it may be, from the same stones. And it cannot be doubted
that the dichroism of the emerald plays a part in producing its
peculiar colour effect. The aquamarine is also dichroic, a sea green
specimen showing straw white and grey blue as twin colours.
The range of colour in the beryl is not very extensive ; colourless
specimens occur, but usually the palest beryls have a faint greenish
or bluish tint. The most usual colours are pale green and pale
blue with intermediate hues. The true deep rich green of the
emerald is rare, but pale yellow, honey yellow, and yellow brown
beryls are not uncommon. Sometimes this stone occurs with a
rose tint.
The best emeralds occur near Muzo, about ninety-seven miles
N.N.W. of Bogota in the Republic of Colombia, South America.
The stones occur in isolated and implanted crystals and in geodes
in a calcareous rock in which are very fossiliferous concretions
of bituminous character ; the emeralds are accompanied by calc-
spar, gypsum, quartz, pyrites and parisite. The rock belongs to the
Neocomian formation. From this locality and from another known
as Somondoco and situated about half a degree east of Bogota,
it is probable that the fine emeralds secured by the Spaniards
in their South American conquests of the i6th century had
been originally derived. The really ancient source of emeralds
before the discovery of the New World is, however, to be found in
Upper Egypt : the mines occur in a depression of the mountainous
range which borders the Western coast of the Red Sea. One group
of mines is situated on Mount Sakketto, the other on Mount Sabara .
The gems are generally full of flaws and poorer in colour than the
fine specimens from Colombia.
Fine beryls occur in the Urals at several localities in the neigh-
bourhood of Ekaterinbarg, especially near Mursinska. There are
other Siberian localities of importance where good aquamarines
are found. In this connection must be named the occurrence
&ERYL. 8 9
+
of fine stones in several places in the United States of America,
in Brazil, and in British India. Beryl, or, rather, aquamarine,
has been long worked in the District of Coimbatore in the Province
of Madras.
Common beryls, but of muddy and even opaque hues, are some-
times found of enormous size. One from Grafton, New Hampshire,
U.S., weighs zqoolb. It is 4ft. 3in. long, 32in. in one direction
and 22in. in another, transverse to the last, across the crystal.
A still larger crystal from the same locality was estimated to
weigh nearly 2j tons. But some of the Russian aquamarines and
transparent or precious beryls are of considerable size and without
flaw. An aquamarine weighing 225 troy ounces, and without a
flaw, belonged to the emperor of Brazil. Good specimens may be
seen in the Mineralogical Gallery of the British Museum. Emeralds
are rarely free from flaws, even in the case of small stones. So
large and finely-coloured an emerald as No. 1284 in the Townshend
collection is an exceptional stone ; it is nearly J an inch across.
The emerald is usually step, that is, trap cut ; the table should
not be large. Perfect stones of the* best colour, and without flaws,
sell for 40 to 60, occasionally even 140, per carat.
The emerald and the aquamarine consist essentially of a silicate
of alumina and of the rare earth glucina. In the emerald Wohler
has confirmed the presence of enough oxide of chromium to cause
the green colour, for he coloured white glass with the same pro-
portion, 0*19 per cent. Neglecting the oxide of iron, occurring
in all varieties of beryl, and also the water and traces of other com-
pounds, the composition in 100 parts of this mineral species will be :
Silica . . . . 66'8 j Alumina . . . . 19 '1
Glucina .... 14*1
The emerald was employed in antique Roman jewellery, some-
tim33 in the form of slices of the native prisms, sometimes in beads,
and very rarely for intaglios. Antique engraved gems of beryl
or aquamarine are not quite so rare.
go PRECIOUS STONES.
The smaragdus of Theophrastus included with the beryl a num-
ber of quite different stones, such as the chrysocolla and dioptase.
Pliny's smaragdus included, besides the above, the green chryso-
beryl and the chrysoprase, as well as the green plasma, the prase,
and green jasper. In native East Indian jewellery the emerald
is usually cut en cabochon ; this form conceals the flaws to a great
degree. In Europe the step-cut is considered the most suitable
style. Emeralds are occasionally engraved or carved. In the
Hope collection there was a beautiful vinaigrette made out of two
emeralds, f inch in height, and J inch across ; it brought 145
guineas when sold by auction in 1886.
CHRYSOBERYL.
The cymophane or true cat's-eye, the hard specimens called
oriental chrysolite by jewellers, and the alexandrite are varieties of
chrysoberyl. Their differences of hue and of physical appearance
are not associated with any essential differences of composition.
The colours of chrysoberyl range from columbine red through
brownish yellow to leaf green ; a golden yellow and a greenish
yellow are not unusual. The coloured chrysoberyls are strongly
dichroic ;* some brownish specimens from this cause may present
to the unassisted eye the aspect of tourmalines. The green leaf,
or deep olive green variety, known as alexandrite, of which fine
flawless specimens of large size have been sent from Ceylon, is
remarkable for appearing of a raspberry red hue by candle or
lamplight. This mineral crystallises in the orthorhombic system ;
twins are frequent. The hardness of chrysoberyl approaches
that of the sapphire : it is 8*5. Its lustre and brilliancy are con-
siderable. Its specific gravity averages 3.7; it is but slightty
lowered by strong ignition.
Golden yellow . . 3'84 I Brownish yellow . . 3'734
Greenish yellow . . 3'76 | Alexandrite . . . 3'644
* Fig. 9. Frontispiece.
'PH EN A KITE. 91
*
The cymophane, or true cat's-eye, owes its chatoyancy, whether
of pale steely whiteness as a flash, or as a line like a silver wire,
to the orderly arrangement of an immense number of minute
cavities along certain lines causing minute internal striations.
The dark yellowish green hue is most prized ; it is usually cut
en cabochon. The chrysoberyl occurs in many localities, notably
in Brazil and Ceylon, Connecticut, and the Urals. A fine specimen
from the Hope collection is in the British Museum.
The chrysoberyl owes its colour chiefly to iron in the form of
ferrous oxide ; but traces of chromium and of manganese oxide
also occur in it. Its percentage composition is roughly :
Alumina . . . . 78 | Glucina . . . .18
Ferrous oxide . . .4
PHENAKITE.
Phenakite is but rarely used as a gem-stone. The colourless
transparent variety may, however, be mistaken for a diamond,
especially by candlelight, when the prismatic colours, or " fire," of
a brilliant-cut specimen are conspicuous. The hardness of this
stone lies between 7 J and 8, while its specific gravity is close upon
3. Crystals of phenakite usually take the form of a low obtuse
rhombohedron. This mineral is sometimes perfectly colourless
and transparent, but more frequently is rather clouded and milky,
or of a straw, sherry, or cinnamon tint. When viewed with a
dichroiscope the ordinary image is colourless, the extraordinary
image being of a warm yellow or brown, should the specimen ex-
amined possess any colour at all.
The best specimens of phenakite known come from the emerald
and chrysoberyl mines at Takovaya, eighty-five versts east of
Ekaterinburg, Perm, Asiatic Russia : the matrix is a mica-schist ;
less important examples are found in Colorado, U.S.A.
In the Mineralogical Gallery of the British Natural History
Museum, there are fine specimens of phenakite both in crystals
92 PRECIOUS STONES.
and in cut form : two of the latter weigh respectively, 43 and 34
carats.
Phenakite is one of the five species of precious stones which con-
tain the earth glucina as an essential constituent the others are
beryllonite, euclase, beryl, and chrysoberyl. Its percentage com-
position is represented by the numbers :
Silica . . . . 54-2 | Glucina . . .45-8
EUCLASE.
Euclase is rarely used as a gem stone. It varies in hue from a
pale straw colour through many qualities of green to indigo blue.
Its hardness is 7*5, and its specific gravity about 3*1. It crystal-
lises in the monoclinic system, and exhibits trichroism. Fine crys-
tals came from the neighbourhood of Villa Rica, Brazil, where
it was associated with topaz in a chloritic schist. It occurs in the
Urals. Its composition in 100 parts is approximately :
Silica . . . . 41 2 [ Glucina . . . . 17'4
Alumina . . . . 35 -2 | Water . . . . 6 '2
Traces of iron, lime, tin and fluorine occur in euclase.
Beryllonite, another mineral species containing the earth beryllia
( = glucina) has been cut occasionally as a gem stone. It is a sodium
glucinum phosphate, and crystallises in the rhombic system. It
occurs at Stoneham, Maine, U.S.A. Beryllonite is transparent and
colourless and presents no valuable optical characters entitling it
to rank as a precious stone. It is, moreover, brittle and of no more
than 6 degrees of hardness. But to the chemist its strange com-
position is interesting, while to the crystallographer its complex
forms appeal.
ZIRCON.
The gem-stones known as jargoons as well as the true hyacinths or
jacinths belong to the same mineral species. There are many cii cum-
stances which unite to make the zircon a beautiful and interesting
ZIRCON.
93
gem. For it presents a considerable range of rich as well as of
delicate hues; its surface lustre is brilliant, almost adamantine ;
while its chemical composition is rendered noteworthy through the
predominant presence of the rare earth zirconia. Although zircon,
even in its most richly coloured varieties, is but feebly dichroic,
yet some specimens display a considerable amount of " fire," owing
to their high dispersive power, while the majority depend for their
brilliancy mainly upon their strong refraction of light, which ap-
proaches that of diamond. Moreover the spectroscope reveals the
presence, in many of the transparent specimens, of a series of black
absorption bands (discovered by the author in 1866), which are
characteristic, and have been attributed to small quantities of a
uranium compound, to erbium and to an unknown element.* Zircon
crystallises in the tetragonal system, and usually occurs in short
square prisms terminated by pyramids containing facets of tetra-
gonal octohedra. Its hardness is about 7*5, but rather lower than
this figure in the varieties of lower density. The specific gravity
of zircon demands special consideration, as this physical property pre-
sents, in the case of this mineral, features of quite singular interest.
In fact the specific gravity of different specimens ranges from 3-98 to
4*86, a range more extensive than that of any other precious stone,
indeed of any other mineral. Of the gem- varieties of zircon the
least dense are those which are of a pure leaf-green colour, 3*98
to 4-18 ; then come the paler and duller green stones, 4*2 to 4*4 ;
then the clouded orange or gold-coloured stones, 4*32 to 4-45 ;
then the great bulk of yellow, orange, red, brown, puce, and white
stones, 4'6 to 475 ; the flame-red zircons of Expailly, Auvergne,
with a density approaching 4*86 conclude the series. The follow-
ing set of determinations of the specific gravity of flawless cut speci-
mens of zircon (both jargoons and hyacinths) will be useful for
reference, particularly as the numbers represent the values obtained
* Fig. 11. Frontispiece.
94
PRECIOUS STONES.
for stones of volume sufficient to secure accuracy ; all the speci-
mens save one were from Ceylon :
Pure leaf-green
Pale grey-green
Golden
slightly opalescent .
3-982
4-023
4-055
4-076
4-256
4-314
4-346
4-316
4-432
Golden, slightly opalescent . 4-449
Greenish yellow . . . 4 '572
Yellow 4-623
..... . 4-630
Puce . . , . . 4-643
Deep red . . . .4-681
(Mudgee) . . 4-705
Pure white .... 4-687
1-705
This tabular statement of specific gravities would be incomplete
without reference to the change which many zircons undergo when
strongly heated most coloured zircons thus lose or change their
original hue. Some become nearly or quite colourless, others from
a brown or reddish hue change to a dull green. Now it is found that
zircons naturally of high density are not altered in this character by
heating, but, on the other hand, that specimens of low density usually
contract considerably after having been raised to a high tempera-
ture. Thus a green stone, having the low density of 4*0 acquired
a density of 4*31 after it had been strongly heated ; while a gold-
coloured specimen was raised from 4*375 to 4 '657. Yet so long
ago as 1875 I described a low density dull green zircon which suffered
no condensation by being heated but retained its original density
of 4*02. The recent researches of Dr. S. Stevanovic and of Mr.
L. J. Spencer point to the existence of three modifications of zir-
con-material. One of these has a permanent density of 4 ; another
has the same density, which, however, can be raised by heating ;
a third modification has the permanent density of 4*7. All the
different densities and changes of density which have been observed
can be explained on this hypothesis.
Several curious phenomena are presented by certain varieties of
zircon. For example, all the bright green stones of low density as
well as some others of ill-defined greyish yellow and greenish yellow
ZIRCON,
95
hues give rise to a brilliant orange light when apjflied to a copper- wheel
charged with diamond dust in the operation of grinding. Then again
the gold-coloured zircons having a density of about 4 . 4 continuously
glow with a fine orange incandescence in the flame of aBunsen-burner ;
this effect is apparently produced by the presence of thoria.
Ceylon yields the finest and largest specimens of precious zircon.
New South Wales contains several deposits in which beautiful zir-
cons occur : the stones from Mudgee have been known for some
years. The zircons from Expailly in Auvergne are quite typical
hyacinths ; they possess a beautiful aurora-red hue, but are as a rule,
very small. The market-value of the gem-varieties of zircon is
small. Fine red columbine red and cinnamon-hued stones may be
bought at 53. per carat : yellow stones and dull green specimens are
still cheaper, but the deep and rich leaf green stones and even those
which are of a pale though pure green colour, as also those which
are brilliantly white, bring larger sums. The largest " camellia-leaf "
green zircon, weighing over 19 carats, with which I am acquainted
brought 26s. the carat. But it was London-cut and no doubt
weighed 5 or 6 carats more when imported in its native cut state.
Such a stone, of the same high quality and colour and weighing
i8J carats cost 18 IDS. in Ceylon : but it had to be re-cut and lost
2 carats in the operation.
White or colourless zircons are used in lieu of diamonds by
wealthy natives in Ceylon. They have been employed in European
jewellery also ; sometimes a fine white zircon set in a massive ring
of gold has been pawned as a brilliant, and not redeemed. A file
will not scratch a facet of a zircon, so that this test for " paste " is
inapplicable. But though much harder than glass, and harder even
than rock crystal, zircon is unfortunately somewhat brittle, and
easily becomes chipped in wear. An examination of a large num-
ber of engraved gems labelled hyacinth or jacinth has proved them
not to be of true hyacinth, that is red zircon, but of garnet, either
hessonite or cinnamon stone, or of almandine.
9 6 PRECIOUS STONES.
Putting on one side minor and accidental ingredients, although
to these the colours, absorption-bands, opalescence, etc., of the
stone are due, the percentage composition of zircon approaches,
Zirconia . . . . 67 | Silica 33
SPODUMENE.
Until lately spodumene was not recognised as a stone which
could be cut and polished as a gem ; but a large importation from
Brazil of brilliant and transparent crystals of yellow spodumene led
to some specimens being cut and polished. The easy cleavage of
the stone renders its working and mounting difficult matters. Spo-
dumene crystallizes in the monoclinic system, and resembles in
appearance the chrysoberyl. Its hardness is 7, and its specific
gravity 3*2. It contains in 100 parts :
Silica . . . .64-2
Alumina . 29*0
Iron oxk'e .... '4
Lithia. , 6'0
with traces of soda, lime, potash, and water.
HlDDENITE.
This beautiful green stone is transparent and of a brilliant green
hue, not unlike that of a rather yellowish green emerald. It is
a variety of spodumene, a mineral generally of a dull well-nigh
opaque greyish or creamy colour, but sometimes of a brilliant
straw yellow and transparent. Hiddenite rarely occurs in crystals
sufficiently large for cutting into gem-stones. A cut stone, how-
ever, nearly perfect, weighed 2j carats, and was sold for more
than $125 a carat. It has been found as yet in but one locality,
Alexander county, North Carolina. It was discovered by Mr.
W. E. Hidden. Its hardness is 6|, and its specific gravity 3*17.
KUNZITE.
This newly- discovered variety of spodumene is remarkable
for the very large size of the crystals in which it occurs, for the
OPAL 97
peculiar rosy lilac hue which it presents and lor its perfect trans-
parency. Many brilliant and perfect cut stones have been
fashioned from this variety of spodumene, which is found near
Pala, in San Diego County, California, at a locality famous for
its lithia minerals, such as lepidolite, amblygonite and tourmaline.
Kunzite, so named after Dr. G. F. Kunz, the gem expert, resembles
the yellow spodumene of Brazil, and the green spodumene (hidden-
ite) of North Carolina, in its transparency, its easy cleavage, its
hardness of 6f, and its specific gravity of 3*18, but, unlike these
varieties, it exhibits a characteristic phosphorescence after ex-
posure to the influence of radium bromide and of the X-rays.
As the colour of this mineral is pale it is seen to perfection only
in somewhat large specimens for example, in a brilliant-cut
stone of 20 carats or more. This is the case with the precious
stone which Kunzite most nearly resembles in hue, namely, pink
topaz.
OPAL.
Among the numerous forms or varieties of the mineral species
called opal one kind alone is prized as a gem-stone. This is the
noble or precious opal, which is distinguished by its play of brilliant
rainbow colours. These are not caused by any coloured sub-
stances as constituents, but are due to a peculiar structure of
this mineral. Although by transmitted light the precious opal
appears milky or cloudy and yellow, by reflected light it exhibits
orange, red, blue, green, and many other beautiful hues. These
colours are produced by a mechanical or physical structure, which
consists of a multitude of fissures, the sides of which are minutely
striated, and which causes the diffraction and decomposition of the
white light which falls upon them. The size of these str ations
and fissures influences the colour and its distribution within the
stone, some specimens showing a predominance of one set of hues,
say red and orange, and others exhibiting chiefly green, sea green,
8445. G
98 PRECIOUS STONES.
and blue tints. Sometimes, too, the patches of colour are of
moderate and uniform size ; sometimes they are large and irregular.
The precious opal is, moreover, sometimes so milky as to be almost
opaque ; sometimes, as in many Queensland and Honduras
specimens, it is nearly as transparent as glass. An intermediate
condition, provided the fiery play of colours be well developed,
is most highly prized ; the best opals from Hungary and many
of those from Mexico and from New South Wales are of this
kind.
The opal consists essentially of silica, but it differs from quartz
that is, rock crystal in two important particulars : it is vitre-
ous, not crystalline, and it contains combined water. The precious
or noble opal usually contains from 9 to 12 parts of water in 100 ;
but it may be dried so as to lose for a time a small part of this
moisture without injury to its beauty.; in fact, the whole of the
water present is not essential to the mineral. The specific gravity
of opal is lower than that of quartz or rock crystal about 2*2.
Its hardness is about 6, or even as low as 5*5. Its fragility and
softness, and its liability to injury from oily or greasy matter,
render the opal unfit for a ring-stone, but it may be used to advan-
tage, in pendants, bracelets, and ornaments for the head. A foolish
but prevalent notion that the opal carries bad luck with it is of
quite modern origin, but lowers the commercial value of the stone.
Moreover, the great diversity in the quality of this gem renders
it impossible to assign definite prices to opals of definite weights,
though it may be said that a fine opal of i carat is worth about 2.
Besides the more usual form of precious opal, we have the Mexi-
can fire opal, showing, along with a slight cloudiness, a rich orange-
red hue like that of a glowing fire ; and the harlequin opal, in which
the brilliant patches of colour are small, angular, variously tinted,
and uniformly distributed. The common or non-prismatic opal
is found of many hues, rose-coloured, green, milky, agatoid, and
with dendritic markings. Hydrophane is a variety which becomes
QUARTZ. 99
transparent, and sometimes even shows coldurs when saturated
with water ; hyalite is transparent ; cacholong is milky and nearly
opaque.
Opals are cut with a convex surface ; their brilliancy is often
increased by moderate warmth.
Root of opal contains veins and specks of opal in a dark-coloured
ferruginous matrix, which may be still further darkened by soaking
in oil of vitriol. Cameos are sometimes cut so as to show a head
or figure in precious opal thrown up against a background of the
dark-brown ferruginous matrix of the stone.
QUARTZ.
The purest form of quartz is represented by the colourless rock
crystal so largely used for ornamental objects in the cinquecento
time, and now employed extensively for optical purposes. It is
silica, the oxide of silicon (Si0 2 ), and contains 47-0 per cent, silicon
and 53*0 per cent, oxygen. The coloured varieties contain some-
times very small traces of foreign matters to which it is presumed
their colours are due : but there are doubts in many cases as to
the exact nature of the causes of these colorations when they are
not of merely mechanical or physical origin. The presence of
nickel compounds in the green chrysoprase, and of titanium in
the rose quartz of Rabenstein is believed to be the cause, in these
instances respectively, of the colours of these two varieties of quartz ;
moreover, there is no doubt that many of the red, green, and brown
colours shown by members of this group are due to manganese
and iron oxides, and to silicates of these metals. Traces of water,
alumina, lime, and magnesia also occur, but these ingredients are
of little importance as regards the source of the hue of different
varieties of quartz.
Quartz crystallises in the rhombohedral system, its commonest
form being a six-sided prism, striated transversely, and terminated
by a six-sided pyramid. In amethyst there are many fine
8445. G 2
ioo PRECIOUS STONES.
undulatory layers, so superimposed that a slice across a crystal shows
their triangular section distinctly, and reveals as it is turned round
the difference of colour caused by their structure and arrangement.
The alternate layers are endowed with right and left handed powers
of rotatory polarisation. The " rippled " fracture, and the feathery
flaws of amethysts are due to these fine layers.
Quartz is doubly refractive : the coloured specimens are dichroic.
The indices of refraction for the yellow ray are w = i 5442 and
e = 1-5533. The colours of oppositely polarized rays are, in the
case of the amethyst, reddish purple and bluish purple.
The hardness of pure rock crystal is 7, and its specific gravity
2-65. A list of specific gravities of some of the purest forms of
quartz will be useful, but it must be remembered that the dark
coloured and opaque varieties are much denser, sometimes reaching
2'8.
Milky quartz . . . 2 '642 1 Brown cairngorm . . 2'656
Pure rock crystal . . 2'650 Amethyst . . . 2 "659
Very dark ditto . . 2 '662
Quartz may be melted by the aid of the oxyhydrogen blowpipe
to a limpid glass having the specific gravity 2' 2 and the hardness 5.
The very numerous varieties of quartz cannot be classified accu-
rately, for many of them owe their peculiarities to intruding minerals
of many sorts. The quartz cat's-eye includes fine fibres of asbestos
or crocidolite ; avanturine qua r tz, minute spangles of mica ; and
so on. But the pellucid varieties group themselves near rock
crystal, while the translucent kinds may be arranged under chalce-
dony. The former group includes amethyst and cairngorm, the
latter sard, chrysoprase, and plasma. We cannot here find space
for more than an alphabetical list of the chief members of the great
quartz family.
Agate --layers of chalcedony, jasper, rock crystal ; also mottled.
Agate-jasper a variety of agate containing jasper.
Amethyst transparent, purple, honey yellow or greenish yellow.
Avanturine transparent, with go 1 . den brown or green iridescent spangles. '
QUARTZ. ioi
4?
Beekite silicified corals, shells, or limestone, resembling chalcedony.
Bloodstone translucent to opaque ; green with red spots.
Cairngorm transparent and smoke grey, yellow or brown.
Cat's-eye translucent grey or greenish, with chatoyancy.
Chalcedony- cloudy or translucent ; white, yellow, brown, blue.
Chrysoprase translucent ; pale bluish green.
Cornelian translucent, like horn ; yellow, brown, red.
Egyptian jasper opaque, concentric, and other layers of yellow, brown, or
black. '
Heliotrope a chalce Ionic base, with much green delessite (chlorite) and red
spots of iron oxide.
Jasper opaque ; dull red, dull green, and ochre yellow.
Milky quartz opalescent or milky, yellowish by transmitted light.
Onyx bands or strata of white, grey, black ; translucent to opaque.
Plasma very translucent ; rich leaf green.
Porcelain jasper sub-translucent ; often white and pink.
Prase translucent, but spotted ; muddy olive green.
Riband jasper opaque bands, dull red and dull green ; sometimes yellow.
Rock crystal- transparent and colourless.
Hose quartz transulceut and pale pink.
Sapphirim quartz translucent and pale greyish blue.
Sard very translucent ; red, brownish red, crimson, blood red, blackish red,
golden, amber.
Sardonyx- a stratified stone, having one or more strata of sard.
Smoky quartz transparent ; of various hues of grey and brown.
But this list by no means exhausts the varieties of quartz, for of
agate alone we have fortification agate, moss agate, and mocha
stone, eye agate, and brecciated agate. All of these stones, and
indeed the majority of those in the list just given, so far as their
colours and markings are natural and not due to artificial treat-
ment, consist of amorphous or crystalline silica, variously arranged
or disposed, and associated with colouring oxides and silicates con-
taining oxides of iron, manganese, or nickel. The claim of very few
of these varieties of quartz to the rank of precious stones can be
sustained. It is not merely that they are abundant, but their
brilliancy and beauty are not sufficiently pronounced to entitle them
to high rank amongst stones for jewels. The great merit of the
artistic work executed in these materials, in Greek, Roman, and
cinque-cento times has indeed ennobled the sard, the onyx, the prase,
102 PRECIOUS STONES.
the sapphirine quartz, the jasper, etc ; but except in the forms
of cameos and intaglios these stones are but little esteemed. Rich
deep-coloured amethysts, with the colour not quite uniformly
distributed throughout their substance, are perhaps the most prized
form of quartz. The colour of such amethysts gains in beauty
from the dichroism of the stone and from its peculiar rippled and
parquetry structure. Such amethysts are wrongly called oriental
amethysts by jewellers (some do come from India), for the true
oriental amethyst is a purple sapphire, not quartz at all, and an
excessively rare stone.
The localities for choice specimens of amethyst, sard, chrysoprase,
chalcedony, etc. are legion. The amethysts of Brazil and Ceylon,
the agates of Uruguay, the chrysoprases of Silesia, the cornelians of
Arabia, and the jaspers of Egypt are famous.
Not only have the dark-coloured onyxes of commerce been artifi-
cially dyed or stained, but a large proportion of agates, cornelians,
sards, etc. have been similarly altered. A moderate heat reddens
many varieties of quartz originally grey and brown, while a soaking
in sugar or honey, followed by treatment with strong sulphuric acid,
brings out black and white bands in the natural grey onyx.
Hydrochloric acid develops a lemon -yellow colour in white
chalcedony, while a strong blue colour may be imparted by causing
Prussian Blue to be precipitated within the stone by alternate
soaking in solutions of green vitriol and of prussiate of potash.
LAPIS-LAZULI.
Lapis-lazuli or azure stone is not a definite mineraj but a mixture,
in variable proportions, of several minerals. Generally calcite
forms the chief part of the colourless patches in the stone, but there
will be present two or even three complex silicates possessing a
beautiful blue colour. One of these is known as Haiiyne or Haiiy-
nite, another is true ultramarine, and another is called sodalite.
They are all silicates and all contain much alumina; but soda is also
LAPIS-LAZULI. 103
*
present, as well as lime and iron. But it is the presence of sulphur
in two forms of combination, namely as sulphide and as sulphate,
which distinguishes the blue pigment, obtained by the treatment
of lapis-lazuli, from all other blue compounds. This pigment has
been very successfully imitated, not only as to colour but as to
chemical constituents, by chemical art. It should be added here
that the minute brass yellow specks, or spangles which are com-
monly seen in lapis, are iron pyrites. Lapis was the sapphire of
the ancients.
Lapis-lazuli occurs in Transylvania, Siberia, Tartary, Persia,
China, Thibet and Brazil. The richly coloured varieties are used
for beads and for mosaic work and inlays in bijouterie, vases, furni-
ture, and even in the internal decoration of buildings.
The hardness of lapis-lazuli lies between 5 and 5*5; its specific
gravity is about 2*4. By moderate heating the blue colour of this
mineral is generally unaffected, though in some cases it may actually
be deepened. Carbonic acid does not affect it, nor does a cold weak
solution of alum. Strong acids decompose it, the colour disap-
pearing and sulphuretted hydrogen being given off.
The blue mineral called lazulite, although it sometimes presents
an appearance slightly resembling that of lapis-lazuli, is not con-
nected with the latter species by chemical constitution, for it is a
phosphate, not a silicate (see page 72, under turquoise).
A thin section of lapis-lazuli constitutes a most beautiful
microscopic slide. The perfect transparency and superb colour of
the blue portions are characteristic. Until thus seen by transmitted
light it would not be imagined that a mineral which appears by re-
flected light to be almost opaque could allow the passage of so
much light through it.
lOLITE,
Called also dichroite and saphir d'eau, and known to mineralogists
as cordierite, is a beautiful and curious stone, remarkable for its
104 PRECIOUS STONES.
pleochroism. Its crystals belong to the rhombic system. Good
specimens, such as are occasionally met with in Ceylon, show in
different directions of the crystal a soft lavender-blue, a greyish
white, and a straw colour.* lolite is frequently full of flaws and
almost opaque ; its beautiful change of colour is then very imper-
fectly seen. The hardness of iolite is above 7 ; its specific gravity
is 2*6 to 2'66. One hundred parts of iolite on an average contain
about :
Silica 49
Alumina .... 33
Ferrous oxide ... 5
Magnesia . . . .10
Lime . ... . 1
Water 1
CROCIDOLITE
Is, or rather gives rise to, one of the minerals which has been termed
cat's-eye. It occurs of three distinct colours brownish yellow or
gold (tiger eye), indigo or greenish blue, and dull red. When cut
en cabockon of an oval form, with a high ridge, and with the longer
diameter of the oval at right angles to the direction of the fibres or
filaments which the mineral includes, crocidolite shows -a good line
of light and presents a brilliant appearance. It always contains
a chalcedonic base ; indeed the best specimens, which now come
from Griqualand West, South Africa, and have a hardness of nearly
7, and specific gravity of 2*8, are essentially pseudomorphs after
crocidolite, and not the unchanged mineral itself, which is softer
and heavier. This stone is related to hornblende and asbestos, and
has approximately this composition in 100 parts :
Silica 51
Oxides of iron 34
Soda 7
Magnesia 2
Water 3
Bronzite and Hypersthene are two other minerals, resembling
crocidolite in their metallic reflections, and consisting of silica,
iron oxides, and magnesia.
* Frontispiece, Fig. 5.
LABRADORITE. 105
LABRADORITE.
Labrador spar is a felspar, crystallising in the triclinic system. It
is usually translucent rather than transparent, and by transmitted
light appears of a grey colour. Owing chiefly to a peculiarity in
its intimate or minute structure, which resembles a complex system
of gratings, labradorite often shows magnificent chatoyant re-
flections of brilliant blues, sea green, orange, puce, amber, and
peach-blossom hues, in fact, a coloured metallic sheen. It should
be cut with a nearly plane or but slightly convex surface. It
occurs, associated with hypersthene and amphibole, of fine quality
in the island of St. Paul, and in large masses on the coast of
Labrador ; also in Finland, Volhynia, the United States and
Queensland. Labradorite has the hardness 6, and the specific
gravity 2*7 to 2*75. In 100 parts it contains :
Silica ... . . 55 '5 I Iron oxides . .- . 2*0
Alumina . . . .26*5 Lime . . . . ll'O
Soda ... . .4-0
In some specimens there is less lime, but instead, a small per-
centage of potash and magnesia.
MOONSTONE OR ADULARIA.
This is a variety of felspar, or rather of that species of mono-
clinic felspar called orthoclase or orthose. Moonstone is found
at St. Gothard, and very abundantly in Ceylon. It differs from
ordinary orthoclase in the remarkable pearly reflection of light
which it exhibits in certain directions. The most esteemed speci-
mens are those in which the chatoyancy has a distinctly bluish
hue. Some varieties are nearly opaque ; a chocolate-coloured
sort has also been found. The bluish stones only possess a market-
value. The hardness of moonstone is 6, and its specific gravity
almost invariably 2.58. It contains in 100 parts:
Silica .... 64-5 I Alumina . . . . 18'5
Potash . . . .15-0 Soda . . . .TO
with traces of lime, and magnesia.
io6 PRECIOUS STONES.
SUNSTONE OR AVANTURINE FELSPAR
Is usually a variety of oligoclase, or soda lime felspar, having
golden yellow, reddish, or prismatic internal reflections, due to the
presence of minute imbedded and scattered crystals of haematite,
gothite, or mica. Some avanturine, is, however, a mixture of
albite and orthoclase, and the same name is given to quartz con-
taining brilliant imbedded micacious crystals. The green avan-
turine, called amazon-stone, is microcline, a felspar.
OBSIDIAN, OR VOLCANIC GLASS
Is often nothing more than fused or vitreous orthoclase that
is, potash felspar. But obsidian frequently contains many other
minerals in small quantities, such as augite and olivine ; in fact,
obsidian is a melted lava, and contains the various minerals of
the lava melted or else associated together. Obsidian when
transparent has about the specific gravity 2*4, and is softer than
crystalline felspar. Black specimens of it resemble black garnet,
spinel, and tourmaline, but are much more translucent in thin
splinters, as well as striated and full of bubbles.
EPIDOTE.
The various hues of olive, brownish, and pistachio green which
are presented by tourmaline occur also in great measure in epidote.
The latter mineral is, however, less dichroic than the former, al-
though in some green Siberian and Brazi ian specimens an emerald
green image and a yellow one may be seen in the dichroiscope.
The most famous locality is the Knappenwand, Salzburg. The
hardness of epidote is about 6*5, and its specific gravity 3*3 to
3-4. It occurs in oblique prisms, often much elongated. Green
epidote presents in 100 parts about the following composition :
Silica 38
. . . .22
Ferric oxide . . .15
Lime . 23
AXINITE. 107
AXINITE.
Although almost a curiosity among gem-stones, yet fine crys-
tals of axinite have been cut for ornamental use. It belongs to
the triclinic system. The hardness of axinite approaches that of
rock crystal, but the brittleness of this substance almost precludes
its being cut. It looks well en cabochon, and incurs in that form
less liability to fracture. The specific gravity of transparent flaw-
less axinite is 3-29 ; its colour ranges between a pale puce, a plum,
and clove brown ; it is generally strongly pleochroic, showing a
white or straw yellow, an olive, and a violet or purple image in
different directions. The best specimens are found at St. Chris tophe
in Oisans, Isere. The presence of boron in axinite is remarkable :
tourmaline is the only other gem-stone in which the element occurs.
The percentage composition of axinite approaches
Silica . . .... 43
Boron trioxide . - . " -5
Alumina, . . , . 16
Ferric oxide ". . . . 3
Ferrous oxide . - . , , . 7
Manganons oxide . . 3
Potash . . . . 1
Lime . . . - . .20
Magnesia .'-..- . . 1
Water . 1
SPHENE.
This mineral, when it occurs in sufficiently large crystals and is
perfectly transparent, is occasionally cut as a gem-stone. Some
beautiful specimens, chiefly of a honey-yellow or greenish-yellow
colour, have been obtained from various localities in Tirol, the
United States and Canada. Sphene or titanite is calcium silico-
tungstate and is remarkable, not only for its dichroism, but also
for its strong dispersive power ; a brilliant -cut stone is full of " fire."
The specific gravity of sphene is about 3*5, but its hardness is low,
just under 5-5. Sphene contains in 100 parts about :
Silica 31
Titanium oxide . 41
Lime.
Ferrous oxide
CASSITERITE, RUTILE, AND ANATASE.
These are binoxides, cassiterite or tinstone being that of tin, the
two* others being distinct forms of titanium binoxide. .Cassiterite^
io8 PRECIOUS STONES.
when perfectly transparent and pale in colour may be cut into
a lustrous gem-stone. Its specific gravity is nearly 7, and its hard-
ness about 6J. Rutile, when of a transparent red colour, yields a
cut stone of very high refractive index, and presents a lustre almost
metallic on the polished surfaces. But Rutile is, perhaps, best
known in the form of acicular crystals, red or reddish-brown in hue,
which, when penetrating rock crystals, constitute the Veneris crinis
of Pliny. Of anatase we need only say that some of the indigo-
blue transparent and splendent crystals from Brazil have been
mounted, either in their natural forms or step-cut, in jewellery.
They have the form of beautiful low octahedra belonging to the
tetragonal system : their specific gravity is about 4-86.
DIOPSIDE.
This mineral has been occasionally cut as a gem-stone ; it pre-
sents a close resemblance to dull green tourmaline or epidote. Its
hardness, however, does not exceed 6. The specific^gravity of a
fine cut diopside was 3*306. Its colour is due to ferrous oxide.
It contains aboat
Silica ..... 54 I Magnesia .
Lime . . . . . 24 I Ferrous oxide
APOPHYLLITE.
Apophyllite can hardly be regarded as a gem-stone, its softness
causing its rapid abrasion. The hardness of apophyllite does not
exceed 5 ; its specific gravity is 2*335 ; its colour varies from nearly
transparent white to grey, yellowish, greenish, and flesh red. This
mineral crystallises in the tetragonal system, the forms assumed
being usually an octahedron, with the solid angles truncated ; the
basal planes have a decided pearly lustre, the other faces are merely
vitreous.
Apophyllite is found in amygdaloid and related rocks, also in
mineral veins, as at the silver mines of Andreasberg in the Hartz.
ANDALUSITE. 109
Greenland, Iceland, the Faroe Islands, also foonah, and Ahmed-
nuggar in India yield fine crystals. It also occurs in many Swedish,
Tyrolese, and Transylvanian localities.
Apophyllite is nearly related to the zeolites, and is a hydrated
silicate of lime and potash, with a little fluorine. Its percentage
composition is represented by the following numbers
Silica 52 I Potash . . . . 5'0
Lime 25 Water .... 16'5
Fluorine ..... 1
ANDALUSITE.
It is seldom that the mineral andulusite occurs in a perfectly
transparent condition fit for cutting as a gem. Its colour is then
of a somewhat reddish hue or pale amber brown, or light bottle
green. But its beauty and interest mainly depend upon its con-
spicuous dichroism. Cut specimens often appear of a greenish
hue. except in some of the end facets where a fine brownish red
occurs.* There thus arises a marked resemblance to alexandrite,
which, however, is not only a much more valuable stone, but
is also heavier and harder. It may also be confused with certain
tourmalines of similar hue, but its specific gravity is rather
greater, while the pyro-electric character of tourmaline affords a
means of distinguishing the two stones.
Andalusite, which crystallises in the rhombic system, occurs
in prismatically developed forms of which the section is nearly
square. Its hardness is at least 7^ and its specific gravity close
to 3*18. Transparent specimens occur in some abundance in
the Minas Novas district of Brazil, but are also found in certain
gem gravels of Ceylon, where the stone is mistaken for tourmaline.
A step- cut shape with few and rather large facets generally suits
andalusite.
The composition of andalusite is identical with that of cyanite
* Fig. 1. Frontispiece.
no PRECIOUS STONES.
a triclinic mineral of a beautiful blue colour. It contains in 100
parts about
Alumina . .62-8 Silica . . 37 '0 Iron oxides . . 0'2
JADE AND JADEITE.
Under the name of jade (a falsely coined word derived through
the French from the Spanish piedra de hyada) two distinct minerals
are included. One of these, the commoner of the two, is also
lighter and softer, and belongs to the species known as hornblende
or amphibole ; to it the name jade (or perhaps preferably nephrite)
should be confined. It is a compact mineral consisting of irregu-
larly interwoven acicular crystals of the sub-species actinolite.
Its surface when polished acquires a soft greasy lustre ; its sub-
stance, though remarkably tough, is easily scratched by rock
crystal. Jade presents a variety of hues ranging from a rather
creamy white through a number of tones of greyish and leaf-
greeri to a deep or blackish green. An ochre-tinted jade also occurs,
as well as examples in which browns and reddish browns, due
to ferric oxide and ferric hydrate, make their appearance. The
dark grey and blackish varieties contain inclusions of chrome
iron. But whatever the colour of jade it is always translucent,
never transparent on the one hand nor opaque on the other. Of
its many varieties perhaps the green of New Zealand and the
white or greenish white sort from Eastern Turkestan are the most
familiar to Europeans.
Jadeite is as tough as jade, and takes the same polish, but it
is much rarer as well as harder and heavier. Moreover it often
presents, even to the unaided eye, an obvious crystalline texture,
while the most esteemed variety is of a brighter and more emerald
like green than any jade. Some specimens show in parts a deli-
cate lilac tinge. It is from Burma that the jadeite worked by
Chinese lapidaries comes. It is never found in such large masses
as those in which jade occurs, but is sometimes of sufficient
PYRITES. in
dimensions to be fashioned into fair-sized bowl* six inches or more
in diameter. Jadeite, especially the emerald green variety, is
however, more generally employed for smaller objects, such as
snuff-bottles, bracelets, carved plaques, inlays, rings and beads.
It belongs to the pyroxene group of minerals and is therefore
nearly related to diopside and to spodumene.
The chief distinctive characters of jade and jadeite may be
summarized in the following tabular statement where the chemical
composition of typical specimens of each species is presented
in percentages :
Jade. Jadeite.
Silica 58-0 .... 58'0
Alumina T3 . . . . 24*5
Ferrous oxide . . . . 2.0 . . . 1-0
Magnesia 24'2 . . . . 1-5
Lime 13'2 .... 2'3
Soda 1-3 . 12-7
Hardness ..... 6 .... 7
Specific gravity . . . . 2-98 . . 3 '33
For further details concerning the archaeology and artistic use
of jade and jadeite reference should be made to Dr. BushelTs
Handbook of Chinese Art, vol. i, pp. 134-150. In Mr. Spencer's
translation of Dr. Max Bauer's " Precious Stones," pp. 458-470,
will be found a full account of the occurrence, composition and
properties of these two minerals.
PYRITES.
There are two minerals having the same two elements in the same
proportions as constituents, but differing in physical and chemical
characters. These two minerals are pyrite or iron pyrites,and marcasite.
Both contain iron and sulphur, 46*7 per cent, of iron, and 53*3 per cent,
sulphur, corresponding to I atom of iron and 2 atoms of sulphur.
The properties of the two minerals may be compared thus :
Pyrite. Marcasite.
Hardness . 6 '5
Specific gravity . , . 5 '2
Crystalline form . . Isometric
Colour .... Brass yellow.
6-0
4-8
Orthorhombic.
Pale or grey yellow.
II2 PRECIOUS STONES.
Pyrites is the more abundant form of this compound of iron and
sulphur. It was largely used in jewellery in the eighteenth century,
and is often incorrectly spoken of as marcasite. It takes a fine
polish and presents the appearance of a metal. It is of no value
whatever from a commercial point of view, although a good deal of
time and trouble were frequently spent in cutting specimens of it
into faceted forms, such as single " roses." Pyrites was used
by the ancient Mexicans along with turquoise and obsidian for
their mosiac inlays and incrustations. In the Christy collection
of the British Museum is a Mexican mask, in which the eyes are re-
presented by hemispheres of pyrites.
HEMATITE.
Black haematite is an oxide of iron occurring under several com-
mon names, as specular iron ore, iron glance, and micacious iron
ore. Its powder is red, though a perfectly polished artificial or
natural surface presents a metallic black lustre with slight irides-
cence. It has been employed, cut en cabochon, to simulate black
pearls. The hardness of the densest haematite is 6*5, and its specific
gravity 5*3. It contains in 100 parts :
Iron . . , . . .70 ! Oxygen .... 30
AMBER
Is hardly to be reckoned amongst precious materials of mineral
origin, for not only is it comparatively abundant, but it is an almost
unchanged vegetable product, a fossilised resin of certain conifers
of tertiary age. Its specific gravity is about ro8, and its hardness,
2*5. When traces of moisture and ash are deducted it contains in
100 parts about :
Carbon . . . .78-5
Hydrogen . . . 10'5
Oxygen . . . .10.5
Sulphur . . . .0.5
Amber, whether from the Baltic shores, Sicily or the coasts of
Norfolk and Suffolk, is essentially the same substance, although
the Sicilian amber sometimes exhibits a deeper and redder or
JET. 113
*
browner hue and often shows a bluish or greenish fluorescence.
The amber from Upper Burma may perhaps be a different resin
but it presents, in many specimens at least, very much of the same
range of yellow hues as Baltic amber. But burmite, as it has been
called, occurs sometimes having a purplish brown colour : in the
Indian Museum at South Kensington there is a specimen of this
kind nearly a foot in length, from King Theebaw's Palace at Man-
dalay. It is carved into the form of a duck. Beads and other
objects of amber are frequently found in early burial places in Europe.
Usually the surfaces have become somewhat darker in colour, less
translucent, and somewhat friable : in some instances, however, the
material has resisted oxidation in a remarkable manner, witness
the amber objects from some of the primitive graves at Abydos
and the beautiful amber cup in the Brighton Museum.
Although imitations of amber in yellow glass may be easily de-
tected by means of their coldness to the touch and by their greater
density, it is more difficult to distinguish copal resin from amber ;
still the odour of the latter when rubbed vigorously affords one
means of identification.
JET.
Jet can hardly be regarded in any sense as a precious stone al-
though it has been used from early times for beads, pins, armlets,
and other objects of personal adornment. Many examples in per-
fect preservation have been found in Celtic and Romano- British
graves. Jet is a dense, homogeneous, perfectly black variety of
coal, having a hardness approaching 4 and a smooth concho'dal
fracture. It is still worked to some extent at Whitby on the York-
shire coast.
MALACHITE.
Malachite is never used in the higher class of jewellery ; its
softness, opacity, and crude hue are not in its favour. In Russia
8440- H
ii 4 PRECIOUS STONES.
veneers of it are employed with very bad effect in the decoration
of vases, furniture, and even doors. Its hardness is 4, and its
specific gravity 4.
The concentric veinings and markings of malachite, showing
its deposition from water, vary in depth of tint and often exhibit
a satiny texture.
Malachite belongs to the hydrated carbonates, and is repre-
represented by the chemical formula Cu C0 3 , Cu H. 2 O 2 ; it is there-
fore near chessylite or azurite 2 Cu C0 3 , Cu H 2 a , Malachite con-
tains, in percentages, about the following proportions of its three
constituents :
Copper oxide . . . 72 | Carbon dioxide . . .20
Water .... 8
LUMACHELLA
Is a precious marble. It consists of a brown limestone, in which
occur numerous fossil shells, having brilliant fiery red, green, or
yellow chatoyant reflections. It comes from Bleiberg in Carinthia,
and from Astrakhan. It is an impure carbonate of lime.
PEARL.
Although nearly all those bivalves which have nacreous shells
do occasionally produce pearls, there are two mollusks which must
be regarded as pearl-bearers par excellence. These are the pearl
oyster and the pearl mussel.
The best-known pearl oyster is the small species, Margaritifera
vulgaris, which yields the famous pearls of Ceylon. A larger species,
Meleagrina margaritifera, occurs in the Persian Gulf, Madagascar,
the west coast of Central America, California, and West Australia.
The shells of these oysters are particularly valued on account of
the mother-of-pearl which they yield. From the pearl-mussel,
Margaritana margarilifera, which belongs to the Family of the
Unionidae, the~pearls of Scotland, North Wales and the English
District are derived. These British pearls possess, 'generally
PEARL. U 5
*
in a very small degree that " orient " or iridescent sheen which
constitutes the peculiar charm of this gem ; but some specimens
of great beauty have been found from time to time. A pearl of
particular purity from the river Conway, North Wales, was pre-
sented to the Queen of Charles II. by Sir R. Wynne, and is now
in the Royal Crown. The author of this handbook has seen a few
fine pearls taken from mussels in the river Irt in Cumberland. The
somewhat clouded " orient " of the majority of British pearls
accords with dead or malt gold and with many deep-coloured stones.
Pearls are sometimes found having a decided tinge of colour ;
rose-coloured, salmon-pink, pale blue, russet-brown, olive-brown
and black pearls are highly esteemed ; dull and muddy hues are
less appreciated, and so also are extremely small pearls, which,
indeed, are by far the most abundant. Pearls may be dyed easily,
and are liable to become discoloured by wear. Pink coral, cut
into suitable forms, is often made to simulate pink pearls, but its
texture is entirely different, and may readily be recognised with
the aid of a pocket lens. Black haematite, one of the chief ores of
iron, makes, when not too highly polished, a passable imitation of a
black pearl ; but nothing is easier than to detect the substitution,
for haematite is more than twice as heavy as the pearl.
The substance of the pearl is identical, or practically identical,
with the nacreous material, the mother-o' -pearl, which lines the
interior of the shell. It consists of that form of calcium carbonate
which is known as aragonite and is rather harder and heavier than
calcite. the other and commoner form. The aragonite in a perfect
pearl is arranged in regular concentric layers, like the coats of an
onion, and is always associated with a small quantity of an organic
substance allied to horn. In some pearls the horn-like body occurs
in larger proportion and may even constitute one or more distinct
layers. And occasionally layers of the commoner form of calcium
carbonate, that is calcite, occur in pearls such layers are quite
dull. The specific gravity of pearls is about 2-67, their hardness
8445, P 2
n6 PRECIOUS STONES.
nearly 4. The delicate colouration of the finest pearls is not due
to any kind of pigment, but to the peculiar " intimate " structure
of the nacre producing colour- effects through interference. Occa-
sionally a dull pearl, when carefully peeled by mechanical means,
will reveal a fine orient beneath, and be consequently greatly im-
proved in appearance by the treatment.
Pearls are secreted by the mantle of the mollusc, and in the
same way as that by which the shell itself is formed. Definite
areas of the mantle have definite functions, secreting, as the case
may be, either aragonite, or calcite or the horn-like substance
already named. According to the position of the pearl in the region
of the mantle a position which is subject to change so will be
the nature of its successive additional coats. But it will be asked
" How does the pearl, the detached pearl for example, first come
into being ?" Its occurrence, if not rare, is at least abnormal, and
is the outcome of irritation to the mantle caused by the intrusion
of some foreign body. This foreign body is usually a minute para-
sitic animal (a Cestode larva), but may be a grain of sand,
or some other solid. The irritation stimulates the secretion of
nacre, and the intruder is sooner or later covered with layer after
layer. The Chinese take advantage of this response to the irrita-
tion caused by the introduction of a foreign body in the case of a
fresh- water mussel (Dipsas plicata). They keep the mussels in
a tank and insert between the shell and the animal rounded bits
of mother-o' -pearl or little metal images of Buddha. In either
case the inserted object becomes slowly coated with nacre and
looks like a pearl : the little figures of Buddha generally become
cemented to the shell ; a specimen may be seen in the shell gallery
of the Natural History Museum.
The value of pearls is increased greatly when a considerable
number of well-matched specimens are got together. But the
market value of pearls depends upon so many factors that, even
for a single pearl of what may be called standard quality, ancj.
CORAL. 117
perfectly spherical form, the price can hardly btf stated with ex-
actness. Such a pearl is perhaps worth 10 if it weigh I carat,
four times as much if it weigh 2 carats, and eight times as much
if it weigh 4 carats. Button-pearls, which have one side convex
and the other flat, are less valuable than round pearls, but pear-
shaped pearls often fetch more. The large irregular and grotesque
pearls called baroque acquire value when set into curious figures
busts, dragons, griffins, fruits, etc. by the aid of gold and enamel
mountings. Fantastic arrangements of this kind exercised the
skill of many i6th and I7th century jewellers, but the artistic
merit of these productions cannot be appraised very highly ; the
chief excuse for their existence must be sought in the difficulty
of making any other use of the misshapen pearls in question.
The Green Vaults of Dresden are rich in specimens of this sort.
It should be mentioned that the majority of pearls used in ordinary
jewellery are half-pearls, that is pearls sawn in half. Seed pearls,
the small pearls attached as pendants to jewels, the pearls sewn
on garments, and necklace pearls, are perforated by careful
drilling
Pearls have been used in almost all parts of the world, and
from very early times, for jewellery and personal adornment.
The pearls set in antique Roman ornaments have rarely survived
intact to the present day. Sometimes the place of a pearl in the
setting is represented by a small brownish residue ; sometimes
the reduced form of the pearl is still to be seen, deprived of much
of its lustre by the long-continued action of water charged with
carbonic and vegetable solvent acids from the earth.
CORAL.
The use of coral in jewellery justifies us in adding a few words
here concerning this product of animal origin. All the white,
pink and red coral used for objects of personal adornment is derived
from a single species, Corallium nobile, belonging to the sub-class
n8 PRECIOUS STONES.
Alcyonaria, class Anthozoa, and sub-kingdom Ccelenterata ; the
rarejblack coral, which is entirely horny and has but a trace of
earthy matter in its composition, belongs to the other sub-class
of Anthozoa, namely, Zoantharia. The solid compact part of
the coral animal, or polypdom, in the case of Corallium nobile,
is mainly calcium carbonate (carbonate of lime), with small quan-
tities of magnesium carbonate, iron oxide, and organic matter ;
the exact nature of the red colouring matter remains unknown.
Coral is mainly obtained from the Mediterranean, the coasts
of Provence, Majorca, Minorca, and North Africa being the best
localities. The coral grows on rocks at depths varying from 30
to 130 fathoms, but a depth of 80 fathoms is considered most
favourable.
The price of coral varies much from five shillings to 120 the
ounce ; the pale rose-pink variety is the most esteemed.
A good series of specimens of coral was bequeathed to the
Museum in 1870 by Mr. Alfred Davis ; it is now in the Branch
Museum at Bethnal Green.
Several beautiful minerals and other natural products not
entitled to rank as precious stones have been described in the
preceding pages. A limit had to be set to the expansion of this
handbook, or space might have been found for notices of apatite,
a calcium fluo or chloro-phosphate with a hardness of 5 and a
density of 3*2. sometimes occurring in perfectly transparent
crystals of leaf -green or sky-blue hues : fluor-spar, a still softer
mineral less suitable for use as a gem ; and idocrase or vesuvianite,
a calcium aluminium silicate much resembling epidote (page 106),
and having a hardness of 6J and" a density of 3*4.
THE TOWNSHEND COLLECTION
OF
PRECIOUS STONES.
IN the year 1869 the South Kensington Museum became possessed
of a valuable collection of precious stones, under the provisions
of the will (dated 6 August, 1863) of the Rev. Chauncy Hare Town-
shend. The following extract from the will refers to this bequest :
I, Chauncy Hare Townshend, late of Down Hill, in the parish of Tottenham
High Cross, in the county of Middlesex, and now of Norfolk Street, Park Lane,
in the Parish of St. George, Hanover Square, in the said county, Clerk, do
hereby revoke all Wills and other Testamentary Dispositions heretofore made
by me, and declare this to be my last Will and Testament. I appoint my
friends Burdett Coutts of Stratton Street, Piccadilly, in the said county of
Middlesex, spinster, and the Reverend Thomas Helmore, Master of Her
Majesty's Choir ati/he Chapel Royal, St. James's, trustees and executors 3f this
my will. I give and bequeath to the Right Honourable Granville George
Leveson Gower, Earl Granvile, or other the President of Her Majesty's Council
on Education for the time being charged with the promotion of Art Education,
now undertaken by the Department of Science and Art, such of my pictures
and water-colour drawings, and engravings and books containing engravings, as
his Lordship, or other the President aforesaid, may think fit to select ; and my
collection of Swiss coins, and my box of precious stones (including such as are
generally kept therein, but which in my absence from England may be with me
on the Continent) ; and my box of cameos (which boxes, for the sake of identity,
I declare to be those which in my absence from England are always deposited
for safe custody with my bankers) ; and the ancient gold watch formerly
belonging to my father, which, being stolen by the celebrated Barrington, was
the cause of his transportation, together with the chain, seal, and keys there-
unto attached ; and also the looking-glass and frame over the dining-room
120 PRECIOUS STONES.
chimney-piece, which frame was carved by Gririling Gibbons, on condition that
the said several articles be never sold or exchanged, but to the intent that the
same may be deposited and kept in the South Kensington Museum, or any
other suitable place which may be provided in substitution for that Museum,
and exhibited to the public, with the other Works of Art which now are or
may be therein.
The Townshend collection of precious stones contains 154 speci-
mens, nearly all of them mounted in gold, as rings. A considerable
number of these specimens once formed part of the famous " Hope
collection," and appear in the " Catalogue of the Collection of
Pearls and Precious Stones formed by H. P. Hope," described by
B. Hertz, 1839. Two copies of this catalogue are in the Art Library,
Victoria and Albert Museum. One of these copies contains MS.
additions, and belonged to Mr. H. Hope, and then to Mr. Townshend:
in it are entries giving the prices paid for many of the specimens.
Many of the specimens are figured in Hertz's " Catalogue " ; fifty
of these illustrations, representing stones now in the Victoria and
Albert Museum, have been reproduced for the present volume.
Mr. Townshend's bequest to the Museum included, besides the
above precious stones, 41 other specimens (Nos. 1791 '69, to
1831 '69). These are engraved gems, some antique and some
modern, chiefly in onyx, cornelian, and sard. One example, how-
ever, is on turquoise, and is remarkable for its size ; it is an ir-
regular octagon, 2 inches long by rather more than ij inch broad.
A catalogue of the Townshend gems was written by the late
Professor Tennant, and published by the Science and Art Depart-
ment in 1870. The author of the present Handbook ofj Precious
Stones has submitted each specimen to such an examination as
could be managed with cut and mounted stones, andjias been
enabled to correct some of the attributions. These corrections
were first made by him in " The Spectator " of July 9th, 1870 ;
they were reproduced in " The Quarterly Journal of Science " for
January, 1871, and were adopted by Mr. Hodder M. Westropp in
his " Manual of Precious Stones," published in 1874.
THE TOWNSHEND COLLECTION. 121
No strictly scientific classification of precious stones is possible.
Those in the Townshend collection have been described in the
same order as that adopted in chapter vii. It so happens that
the diamond, as consisting of the pure element carbon, takes for
every reason the first place ; while the sapphire and ruby, as varie-
ties of corundum, the oxide of aluminium, naturally fall into the
second position. Other species are grouped roughly in accordance
with some prominent constituent :
Characteristic element.
CARBON . . Diamond.
ALUMINIUM . Corundum, spinel, turquoise, topaz, tourmaline, garnet.
MAGNESIUM . Peridot.
GLUCINUM . Beryl, chrysoberyl, phenakite, euclase.
ZIRCONIUM . Zircon.
SILICON . . Opal, quartz, iolite, moonstone.
There are, as might have been expected, some stones unrepre-
sented in the Townshend collection. Amongst these may be
named Alexandrite, Axinite, green garnet or Demantoid, Spes-
sartite, Odontolite, Phenakite, Spodumene, and Sphene. Any one
interested in precious stones should, after inspecting the Townshend
collection, turn to the general collection of rings in the museum.
The beautifully and curiously cut diamond in a ring found at
Petersham (No. 780 1904) ; the two Indian thumb-rings of white
jade (1022 and 1023 1871) ; the Persian turquoise with gold-
inlays (965 1871) ; and the two fine bloodstones, (735 and 749
1871) are specially noticeable.
CATALOGUE OF
THE TOWNSHEND COLLECTION.
DIAMOND.
DIAMOND. A natural crystal of octahedral form, having curved faces, and with
its edges replaced, and so passing into a dodecahedron ; ^ in. diam. ;
claw setting on swing mount. 1172 '69.
DIAMOND. Black, brilliant-cut, nearly circular ; i in. diam. ; bordered with
14 small roses ; coronet mount. 1173 '69.
DIAMOND. Colourless, brilliant-cut, nearly circular ; vV in- diam. ; silver
claw setting, on chased gold shank. 1174 '69.
DIAMOND. Honey yellow, brilliant- cut, circular ; T \ in. diam. ; with 8 roses,
one on each point of the coronet mount. (Hope catalogue, p. 27, No. 19.)
Plate I. fig. 1. 1177 '69
DIAMOND. Pale greyish green, brilliant-cut ; ^r by I i- 5 with 6 roses, one on
each point of the coronet mount. (Hope catalogue, p. 28, No. 24.) Plate
I. fig. 2. 117569.
DIAMOND. Bluish grey, brilliant-cut, circular ; 1 in. diam. ; bordered with
12 brilliants set in silver, on gold mount. 1175 '69.
DIAMOND. Pale indigo blue, brilliant-cut ; W in. by T V in. ; bordered with
12 + 6 != 18 brilliants. 117969.
DIAMOND. Pale pinky cinnamon hue, brilliant-cut ; y\ in. by | in. ; bordered
with 12 small brilliants set in silver, on the openwork mount. (Hope
catalogue, p. 27, No. 15.) Plate I. fig. 3. 1178 '69.
CORUNDUM (including Sapphire and
SAPPHIRE. White, with very pale bluish grey hue, faceted, octagonql, diam.
f| in. ; coronet mount. (Hope catalogue, p. 40, No. 19.) Plate I. fig. 4.
1257 '69.
SAPPHIRE. Straw yellow at the ends, and pale grey in the middle, oval
oblong ; in. by T <% in. and r % in. ; thick coronet mount. (Hope catalogue,
p. 40, No. 13.) Plate I. fig. 5. 1256 '69,
PLATE 1. Diamonds, Corundums, 'turquoise, Topazes,
Tourmalines, Garnets.^
O
/y\A7V
AA/VV
To face page 122.
PLATE II. Garnets, Beryls.
21
To face pugc 123
THE TOWNSHEND COLLECTION. 123
*
SAPPHIRE. Yellow, faceted, oval, % in. by i in. ; coronet mount. 1312 '69.
SAPPHIRE. Apricot colour, octagonal oblong, step-cut ; -^ in. by ^ in. ;
bordered with 34 roses, openwork mount. (Hope catalogue, p. 86, No. 13.)
Plate I. fig. 6. 1260 '69.
SAPPHIRE. Pale lavender blue, en cabochon, prismatic by reason of a flaw,
long oval ; if in. by r T in. ; coronet mount. (Hope catalogue, p. 42,
No. 31.) Plate I. fig. 7. 1238 -'69.
SAPPHIRE. Deep blue, oblong ; T 5 ^ in. by T % in. ; with 3 brilliants on each
shoulder of the. ring, and 4 small roses on the claws of the setting.
1239 '69.
SAPPHIRE. Deep blue, nearly circular ; T V in. diam, ; with 2 pear shaped
brilliants ( in. by in.) on the shoulders, and 10 small brilliants in the
setting. 1240 '69.
SAPPHIRE. Blue, en cabochon, oval ; ^ in. by / in. ; claw mount.
1241 '69.
SAPPHIRE. Blue, faceted, egg-shaped ; f in. by \ in. and ^ in. thick ; coronet
mount. 1242 '69.
STAR SAPPHIRE. Pale grey blue, en cabochon, oval ; ^ in. by -^ in. ; plain
mount. 1243 '69.
STAR SAPPHIRE. Blue, octagonal, en cabochon ; f in. by || in. : bordered
with 47 small brilliants and a socket for another ; in silver setting on
openwork mount. 1244 '69.
STAR SAPPHIRE. Pale blue, hemispherical ; J in. diam. ; bordered with 2
circles of diamonds (26 + 24), and with 27 diamonds on each shoulder of
the ring. 1245 '69.
STAR SAPPHIRE. Pale blue, squarish, with corners rounded ; -^ in. diam. ;
coronet mount. 1246 '69.
SAPPHIRE. Violet or amethystine the oriental amethyst ; faceted oval ;
T V in. by f in. ; bordered with 24 roses set in silver, and bearing 6 brilliants
and 2 roses on each shoulder. (Hope catalogue, p. 39, No. 10.) Plate I.
fig. 8. 1247 '69.
SAPPHIRE. Violet or amethystine the oriental amethyst , oblong, faceted ;
H in. by ^ in. ; bordered by 44 roses set in silver on openwork mount.
1277 '69.
SAPPHIRE. Lavender, faceted, rounded oblong ; -^ in. by j-% in. ; coronet
mount. 124869.
RUBY. Pale claret colour, faceted, oblong ; in. by 3 % in. ; coronet mount.
1280 '69.
RUBY. Fine red, faceted ; { in. by T 3 <r in. ; bordered with 12 brilliants ; solid
mount. 1249 '69.
RUBY. Rich red, Indian polished, subovate ; f in. by | in. ; set with 2
brilliants and 10 sinall roses ; coronet mount. J252 '69,
124 PRECIOUS STONES.
RUBY. Rich red, faceted, oblong, with corners rounded ; | in. by T V in. ;
bordered with 22 brilliants and 2 roses ; openwork mouut. 1253 '69.
RUBY. Red, faceted, with rounded ends ; T V in. by ^in. (flaw at one corner) ;
with 14+8 brilliants and 2 roses as border, and on shank openwork
mount. 1254 '69.
RUBY. Rich red, faceted, circular ; j% in. diam. ; with 12 + 6 brilliants and 2
roses on edge and shank ; openwork mount. 1255 '69.
STAR RUBY. Pink, en cabochon, hemispherical ; yf in. diam. ; claw mount.
125069.
STAR RUBY. Rich colour, en cabochon, oval ; f in. by | in. ; bordered with
35 brilliants ; openwork mount. (Hope catalogue, p. 34, No. 14.) Plate I.
fig. 9. 1251 '69.
CORUNDUM. Translucent clove brown, with grey chatoyancy, and with
iridescence through a flaw ; en cabochon, oval ; & in. by ^ in. ; coronet
mount. (Hope catalogue, p. 42, No. 27.) Plate I. fig. 10. 12.58 '69.
CORUNDUM. Translucent, wine coloured, en cabochon, oval ; f in. by T V in. ;
bordered with 16 roses set in silver on a swing mount. (Hope catologue,
p. 37, No. 15.) Plate I. fig. 11. 1259 -'69.
SPINEL.
SPINEL. Ruby red, faceted ; ^ in. by | in. ; surrounded on edge and shank
by 14 + 8 brilliants +14 + 31 roses altogether 67 diamonds ; openwork
mount. 1326 '69.
SPINEL. Ruby red, square, step-cut ; f in. ; surrounded on edge and shank by
20 + 16 36 brilliants; set lozenge-wise on a plain mount. 1327 '69.
SPINEL. Pale purple, faceted, back step-cut ; \ in. by J in. ; bordered with 37
rose diamonds in openwork mount. 1192 '69
SPINEL. Indigo blue, faceted ; f in. by T \ in ; bordered with 18 rose diamonds.
set in silver on open work mount. 1325 '69.
TURQUOISE.
TURQUOISE. Greenish blue, cut with a female head in relief, nearly circular ;
T % in. diam. ; solid mount. (Hope catalogue, p. 91, No 7.) <Plate I. fig. 12.
1261 '69.
TURQUOISE. Dark rich blue, somewhat mottled and dull, oval, cut en cabo-
chon ; \ in. by ^ in. ; bordered with 14 rose-cut diamonds, each in a little
floret, and with an outer oval of 14 brilliant-cut diamonds, 3 brilliants on
each shoulder of the openwork ring altogether 34 diamonds. 1262 '69.
TURQUOISE. Blue, somewhat earthy, oval, cut en cabochon ; ^ in. by \ in. ;
bordered with 14 brilliants ; openwork mount. 1263 '69.
TURQUOISE. Fine blue, oval cut en cabochon ; T \ in. by / in. ; broad and
thick gold ring. 1264 '69.
TURQUOISE, Deep blue, oval, nearly flat ; | in. by \ in. ; solid mount.
1265 '69.
PLATE III. Chrysoberyl, Zircon, Opals, Quartz.
33
35
36 37
39
41
To face page 124.
3415.
PLATE IV. Quartz, Moonstone.
47
To face page 125
THE TOWNSHEND COLLECTION. 125
TURQUOISE. Rather pale and somewhat greenish blue, heart-shaped, inlaid
with gold wires ; Persian ; in. by | in. ; coronet mount. 1266 '62.
TOPAZ.
TOPAZ. Colourless, brilliant-cut, nearly square, rounded corners ; T \r in. diam. ;
coronet mount. 1308 '69.
TOPAZ. Sherry yellow, faceted oval ; ^f in. by f in. ; bordered with 36 diamonds
set in silver on an openwork mount. 1310 '69.
TOPAZ. Yellow, faceted oblong; 1 ^\ in. by T \ in., and T \ in. thick ; coronet
mount. (Hope catalogue, p. 65, No. 5.) Plate I. fig. 13. 1311 '69.
TOPAZ. Rich yellow, faceted oblong, with slightly convex sides ; 1 T V in. by
ft in., and T V in. thick ; coronet mount. 1313 '69.
TOPAZ. Yellow, with flaws along cleavage planes, step-cut, octagonal oblong ;
& in. by T \ in. ; solid mount, with four claws. 1314 '69.
TOPAZ. Light brown, brilliant-cut ; \ in. by \ in. ; coronet mount.
1315 '69.
TOPAZ. Deep wine yellow, faceted oval ; \\ in. by T \ in., and ^ in. thick ;
coronet mount. 1195 '69.
TOPAZ. Rose pink, faceted oblong ; ^J in. by ^ in. ; coronet mount.
118869.
TOPAZ. Deep rose pink or light claret, faceted oblong ; if in. by -$$ in ;
bordered by 34 roses set in silver on openwork mount. (Hope catalogue,
p. 67, No. 16.) Plate I. fig. 14. 1309 '69.
TOPAZ. Pink, oblong ; f in. by in. ; bordered by 36 roses set in silver on
openwork mount. 1317 '69.
TOPAZ. Sea blue, faceted oval ; ^f in. by |j in., and ^\ in. thick ; coronet
mount. 131669.
TOURMALINE.
TOURMALINE. Rubellite, cloudy red, rose cut, flat at back ; in. diam. ;
coronet mount. (Hope catalogue, p. 72, No. 27.) Plate I. fig. 15.
132069.
TOURMALINE, Rich brown, faceted ; |f in. by in. ; coronet mount. (Hope
catalogue, p. 71, No. 19.) Plate I.'fig. 16. 1275 '69.
TOURMALINE. Deep green, oblong faceted ; ^f in. by ^ in. ; coronet mount.
(Hope catalogue, p. 52, No. 2.) Plate I. fig. 17. 1321 '69.
TOURMALINE. Deep green, oblong table, with step-cut bezil, back step-cut ;
1 in. by f in. and T <V in. thick, coronet mount. (Hope catalogue, p. 70,
No. 3.) Plate I. fig. 18. 1323 '69.
TOURMALINE. Indicolite, indigo blue, oval faceted ; \ in. by T \ in. ; coronet
mount. 1319 '69.
TOURMALINE. Nearly black, large table, faceted, almost square ; \ in. by
i\ in. ; coronet mount. 1294 *69.
i 2 6 PRECIOUS STONES.
GARNET.
GARNET. Pyrope of blood-red colour, round, rose-cut; i in. diam., with
border of 9 brilliants set in the broad edge of the plain solid ring.
1269- '69.
GARNET. Seven pyropes of blood -red colour set in a cluster on a plain mount
1276 '69
GARNET. Carbuncle cut en cabochon and set on foil, oval ; ] : - in. by T \ in. ;
solid claw mount. 1270-69.
GARNET. Almandine, of crimson colour, faceted, nearly circular ; J J by
f in. ; coronet mount. (Hope catalogue, p. 61, No. 13.) Plate I. fig. 19
1271 -'69.
GARNET. Almandine, cut en cabochon, with hollowed back, engraved with a
faun; gin. by | in. ; plain mount. (Hope catalogue, p. 62, No. 24.)
Plate I. fig. 20. 1272 '69.
GARNET. Almandine, fiat, escutcheon-shaped ; T \- in. by x % in. ; claw
mount. 127.3 '69.
GARNET. Deep red, faceted, octagonal ; J% in. diam. ; openwork claw mount.
127369.
GARNET. Brownish red, faceted, oblong ; ^f in. by t % in. ; bordered with
47 rose diamonds, set in silver on openwork mount. (Hope catalogue,
p. 62, No. 23). Plate II. fig. 21. 1274 -'69.
GARNET. Hessoni'te, or cinnamon stone, of aurora red hue, faceted ; | in. by
|f in. ; coronet mount. 1279 '69
GARNET. Hessonite or cinnamon stone, of aurora red hue, carved in high
relief with a bust ; plain mount. 1306 '69.
GARNET. Hessonite, or cinnamon stone, of aurora red hue, oblong ; r <V i n - by
^ in. ; light coronet mount. 1307 '69.
GARNET. Hessonite, or cinnamon stone, of aurora red hue, oblong with rounded
corners, faceted ; in. by f 5 j in. ; coronet mount. (Hope catalogue, p. 53),
No. 6) Plate II. fig. 22. 1318 '69.
PERIDOT.
PERIDOT. Leaf green, engraved with hermaphrodite, tree, and Greek inscrip-
tion ; nearly circular ; j% in. diameter ; plain mount. (Hope catalogue,
p. 84, No. 7.) 1300 ; 69.
PERIDOT. Leaf green, octagonal oblong, step-cut, 1] in. by l in.; coronet
mount, 1301 '69.
PERIDOT. Leaf green, rounded oblong, faceted ; ff in. by T \ in. ; and T 5 Y in.
thick ; solid mount. 1302 '69.
PERIDOT. Rich leaf green, tab'e slightly convex, back, barrel-shaped, with
faceted ends ; l^in. by |4 in. and -# in. thick ; coronet mount.
1303 : 69.
THE TOWNSHEND COLLECTION. 127
BERYL (including Emerald and Aquaniarine) .
EMERALD. Fine colour, polished flat, engraved with Persian characters, oval ;
|| in. by i in. ; coronet mount. (Hope catalogue, p. 45, No. 7.)
Plate II. fig. 23. 1283 '69.
EMERALD. Perfect colour, step-cut, square, set lozenge- wise ; r r T in. diam. ;
bordered with 24 single-cut brilliants, and having on each shoulder of the
ring 4 brilliants and 2 roses. 1284 '69.
EMERALD. With six-rayed black star, subglobular, with face and back
centrally flattened, circular, ^ in. diam. ; plain swing mount. (Hope
catalogue, p. 46, No. 9.) Plate II. fig. 24. 1285 '69.
AQUAMARINE. Sea green, faceted, large table, round ; 1 jf in. diam. and
H in. thick; coronet mounted handle. (Hope catalogue, p. 49, No. 6.)
Plate II. fig. 25. 1286 -'69.
AQUAMARINE. Yellowish green, faceted, large table, oval ; 1^ in. by 1 in.
and H in - thick ; coronet-mounted handle. Hope catalogue, p. 49.
No. 4). Plate II. fig. 26. 1287 '69.
AQUAMARINE. Perfect sea green, faceted, large table, oval, 1 in. by 1 in.
and 1 in. thick ; coronet-mounted handle. (Hope catalogue, p. 48, No. 3.)
Plate II. fig. 27. 128869.
AQUAMARINE. Bluish sea green, faceted, long oblong ; 1 in. by ^ in. and
^ in. thick ; coronet mount. (Hope catalogue, p. 50, No. 12. ) Plate II.
fig. 28. 1289 '69
AQUAMARINE. Pale greenish grey, nearly colourless, step-cut, nearly square ;
^f in. by ^ ; coronet mount. (Hope catalogue, p. 53, No. 4.) Plate II.
fig. 29. 1293-'69.
CHRYSOBERYL (including Cymophane and true Cat's-eye)
CllRYSOBERYL. Yellow, faceted, nearly circular; 1 in. by J| in. ; coronet
mount. 1297 '66.
CHRYSOBERYL. Pale yellowish green, brilliant cut ; } in. by & in. coronet
mount. 1304 '69.
CllYRSOBERYL. Cymophane, showing band of pearly light, circular, cut en
cabochon ; in. diam. ; bordered with 16 diamonds set in silver on open-
work mount, 1328 '69.
CHRYSOBERYL. Cymophane ; in. by fV in. coronet mount. 1329 '69.
CHRYSOBERYL. Cymophane ; ] in. by in. ; bordered with 28 small
brilliants ; plain claw mount. 1330 '69.
CHRYSOBERYL. Cymophane, greenish brown, oval, cut en cabochon ; y in.
diam. ; coronet mount. 1331 '69.
CHRYSOBERYL. Cymophane, oval, cut en cabochon band of white light ;
^| in. by ^ in. ; coronet mount. (Hope catalogue, p. 57, No 10.)
Plate III. fig." 30. 1332 '69.
128 PRECIOUS STONES.
CHRYSOBERYL. Cymophanc of dark green colour with band of bluish light,
oval, cut en cabochon ; i in. by T 5 ^ in. ; coronet mount. (Hope catalogue,
p. 58, No. 19.) Plate III. fig. 31." 1338 '69.
ZIRCON.
ZIRCON, or JARGOON. Rieh brown, f in. by | in. ; plain mount. 1282 '69.
ZIRCON, or JARGOON. Sherry yellow, slightly opalescent, brilliant-cut ;
diam. ^\ in. ; coronet mount. 1281 '69.
ZIRCON, or JARGOON. Pale opalescent green ; \ in. by / in. ; brilliant- cut,
plain mount. 1305 '69.
ZIRCON, or JARGOON. Leaf green, faceted, r V in. by ^ in. ; plain mount.
1322 '69 .
ZIRCON, or JARGOON. Brownish green, brilliant cut, oval ; f in. by f in. ;
coronet mount. (Hope catalogue, p. 56, No. 3.) Plate III. fig. 32.
119469.
ZIRCON, or JARGOON. Brownish green, long oval ; -J-g in. by J s in. ; plain claw
mount. (Hope catalogue, p. 57, No. 6). Plate III. fig. 33. 1298 '69.
OPAL.
OPAL. Precious, with patches of brilliant colour '(the harlequin opal), heart-
shaped ; if in. by fV in. ; bordered with 34 roses, and having 2 roses
and 4 brilliants on each shoulder of the shank ; openwork mount.
1220 '69.
OPAL. Precious, with brilliant red, yellow, and green flashes ; oval ; f in.
by ^ in. ; bordered with 34 diamonds set in silver, and having 3 diamonds
on each shoulder of the shank ; openwork mount. 1221 '69.
OPAL. Precious, long pear-shaped ; ^ in. by ^ in. ; open blue-enamelled
coronet mount, with 6 claws, a brilliant on each claw, and 6 brilliants in
the hollows between the claws. 1222 '69.
OPAL. Precious, with large colour flashes, oval ; -^ in. by -jfa in. ; bordered
with 24 brilliants ; plain mount. 1223 '69.
OPAL. Precious, oval, -J- in. by / T in. ; bordered with 16 roses ; openwork
mount. 1224 '69.
OPAL. Precious, with broad flashes of colour, long oval ; | in. by $ in, ;
claw mount, with blue enamel between the claws. 1225 '68.
OPAL. Precious, Mexican, a fire opal of deep amber colour, with red and
green flashes, long oval ; f in. by T % in. ; blue enamelled border, on gold
mount. (Hope catalogue, p. 79, No. 26.) Plate III. fig. 34. 1226- '69.
OPAL. Precious, Hungaiian, very brilliant harlequin colours; circular;
^ in. diam. ; coronet mount, on chased shank. (Hope catalogue, p. 78,
No. 19.) Plate III. fig. 35, 1227 '69.
OPAL. Precious, Hungarian, oval ; H in. by 1 <J rt in. ; plain mount with claws
Hope catalogue, p. 79, No. 28.) 1228 -'69.
THE TOWNSHEND COLLECTION. 129
tf
OPAL. Precious, a fire-opal of deep amber colour, with orange and green
flashes, oval ; f in. by ^ in. ; plain mount. 1229 '69.
OPAL. Precious, Hungarian, pinkish grey, oval ; f in. by T r 2 - in. ; coronet mount.
(Hope catalogue, p. 81, No. 42.) Plate III. fig. 35. 123069.
OPAL. Precious, Hungarian, liver colour, with purple flashe. c , ovate ; \ in. by
\ in. ; plain mount. (Hope catalogue, p. 81, No. 39.) Plate III. fig. 36.
1231 '69.
OPAL. Hungarian, one-third white, with coloured flashes, two-thirds brown,
oval ; \ in. by ^ in. ; coronet mount. (Hope catalogue, p. 80, No. 34.)
Plate III. fig. 37. 1232 '69.
OPAL. Mexican, deep brown, with play of green light, oval ; ^f in. by f in. ;
coronet mount. (Hope catalogue, page 78, No. 22.) Plate III, fig. 38.
, 123369.
OPAL. Hungarian, grey, with black dendrites and greenish blue flashes,
triangular; \ in. across; coronet mount. (Hope catalogue, p. 80, No. 33.)
Plate III. fig. 39. 1234 '69.
OPAL. Honey yellow, with dendrites, nearly hemispherical ; in. by | in. ;
coronet mount. 1235 '69.
OPAL. Honey yellow, faceted, circular ; -*? in. diam. ; coronet mount.
1236 '69.
QUAKTZ (including Cairngorm, Amethyst, Plasma, Chrysoprase, Chalcedony,
Agate, and Onyx).
ROCK CRYSTAL. Colourless, circular, brilliant cut ; % in. diam. ; coronet
mount. 1180 '69.
CAIRNGORM, OR SMOKY QUARTZ. Octagonal faceted ; J$ in. by ^ i n - ;
coronet mount. 1181 '69.
CAIRNGORM. Straw yellow, faceted ; in. by jfe in., and f in. thick ; coronet
mount. (Hope catalogue, p. 86, No. 9.) Plate III. fig. 40. 1182 '69.
CAIRNGORM. Yellow, oval ; 1 in. by $ in. ; claw mount. 1183 '69.
CAIRNGORM. Yellow, with feather consisting of many minute cavities,
faceted, oblong; 1^ in. by 1 T V in-, and ^ in. thick; coronet mounted
handle. 1185-'69.
AMETHYST AND CAIRNGORM. Purple and smoky, twin stone, each half long
oval, faceted, and in. by $ in. ; plain mount. (Hope catalogue, p. 86,
No. 10.) Plate III. fig. 41. 118669.
AMETHYST. Oval, biconvex lens, containing four large cavities, with movable
liquid and bubbles ; 1 in. by | in. ; plain swing mount. (Hope catalogue,
p. 85, No. 1.) Plate III. fig. 42. 1187 '69.
AMETHYST. Heart-shaped, rose-cut; H in. by H in- 5 coronet mount. (Hope
catalogue, p. 89, No. 29.) 1189- '96,
t30 PRECIOUS STONES.
AMETHYST. Deep coloured, faceted, oval; 1 in. by | in., and -|- in. thick;
coronet mount. (Hope catalogue, p. 88, No. 28.) Plate IV. fig. 43.
H90-'69.
AMETHYST. Rich colour, striped, faceted ; 1 T \ in. by f f in. and i in. thick ;
coronet mount. (Hope catalogue, p. 87, No. 19.) Plate IV. fig. 44.
1191 '69.
QUARTZ. Yellow and pale pink, carved as a monkey's face ; ^ in. by / in. ;
plain mount. (Hope catalogue, p. 95, No. 5.) Plate IV. %. 45.
1193 '96.
PLASMA. Engraved, with a Cupid holding a butterfly over a torch, oval ;
a % in. by $ in. ; plain mount. 1196 '69.
PLASMA. Engraved, with a Cupid resting on a staff, oval ; I in. by ^ in. ;
plain mount- 1197 '69.
PLASMA. Engraved, with two female figures, long oval ; ^[ in. by J in. ;
coronet mount. 1198 '69.
CHRYSOPRASE. Face table cut, back en cabochon, oval ; || in. by | in. ;
solid plain mount. 119969.
CHRYSOPRASK. Engraved in high relief, with laurel-wreathed head, oval ;
1 T V in. by T \ in. ; plain mount. 1200 '69.
CHALCEDONY. Greenish yellow, nearly circular ; ^ in. diam. ; plain mount.
120169.
CHALCEDONY. Yellowish green, en cabochon, oval ; |- in. by / T in. ; solid
chased mount. 1202 '69.
CHALCEDONY. Clouded, dull apple green, en cabochon, oval ; in. by T 7 ? in. ;
coronet mount. 1203 '69.
CHALCEDONY. Grey blue, translucent, engraved with the Olympian Zeus,
convex oval ; ^ in. by T % in. ; plain mount. 1204 '69.
AVANTURINE QUARTZ. Spangled green, oval ; in. by T \ in. ; plain mount.
120569.
AGATE. White chalcedony, with reddish brown patch, oval ; | in. by T \ in. ;
coronet mount. 1206 '69.
AGATE. White chalcedony, with light-brown lines, some concentric, oval ;
} in. by T \ in. ; two perforations ; coronet mount. 1207 '69.
CHALCEDONY ON AMETHYST. The upper chalcedonic layer of brownish white
cut to represent a panther, and a narrow border ; the convex back of
amethyst engraved with a Bacchante ; oval ; ^ in. by ^ in. ; in an
octagonal setting on double swivel-ring. (Hope catalogue, p. 86, No. 5).
Plate IV. fig. 46. 1208 '69.
ONYX. White and brown striped ; ^.T in. by T \ in. ; plain mount. 1209 '69.
ONYX ; EYED AGATE. Hemispherical ; t in. diam. ; corone mount. (Hope
catalogue, p. 92, No. 8.) Plate TV. fig. 47. 1210 '69.
THE TOWNSHEND COLLECTION. 131
ONYX. Three layers, brown, white, and black, oval j* in. by / 2 in. ; plain
solid mount. (Hope catalogue, p. 92, No. 1.) Plate IV. fig. 48.
1211 '69.
CORNELIAN. Red, engraved with Persian characters and foliage, tabular.
| in. by | in. ; plain mount. 1212 '69.
Moss AGATE. Pale purple, chalcedonic base, with jasper ; oval, convex ;
in. by T \ in. ; coronet mount. 1213 --'69.
MOCHA STONE. Grey, with dark-brown den Irites ; oval ; I in. by J| in. ;
coronet mount. 1214 '69.
MOCHA STONE. Grey, with black deudrites, oval ; 1 in. by in. ; coronet
mount. (Hope catalogue, p. 81, No. 40). Plate IV. fig. 49). 1215 '69.
BLOODSTONE, OR HELIOTROPE. Tabular, oval ; ^ in. by |y in. ; plain
mount. 121669.
CAT'S-EYE. Honey yellow, en cabochon, high and narrow ; | in. by ^ lu.
and i\ in. thick ; coronet mount. 1217 '69.
CAT'S-EYE. Pale yellow grey, en cabochon oval, T \ in. by \ in. ; plain
mount. 1218 '69.
CAT'S EYE. Brown, en cabochon, dished back, oval ; f J in. by f$ in. ; bor-
dered with 20 brilliants, and with several roses on the pierced shoulders ;
set in silver on gold shank. 1219 '69.
LAPIS-LAZULI.
LAPIS- LAZULI. Deep blue, with a few minute spangles of pyrites ; tabular,
oval ; / ff in. by ^ in. ; solid mount. 1324 '69.
IOLITE, OR DICHROITE.
IOLITE, OR DICHROITE. Pale violet, showing oblique cleavage lines, en
cabochon, oval ; in. by r \ in. ; claw mount. 1267 '69.
IOLITE, OR DICHROITE. Pale blue, showing oblique cleavage lines, en cabochon
oblong, rounded ends ; J in by \ in. ; claw mount. 1268 : 69.
CROCIDOLITE.
CROCIDOLITE. Dark bluish-green, with band of light, cut en cabochon ', ^ in.
by T 7 in. ; coronet mount. 1336 '69.
FELSPAR.
LABRADORITE, Grey, with blue, green, and orange chatoyancy, slightly,
convex, circular ; xV i n- diam. ; claw mount. 1292 '69.
SUNSTONE. Avanturine felspar of delicate reddish brown colour, en cabochon,
oval ; T \ in. by T \ in. ; solid mount. 1293 '69
MOONSTONE. Adularia, orthoclase felspar, having a bluish-white chatoyancy,
en cabachon, oval ; J in. by r 5 2 - in. ; plain mount. (Hope catalogue, p. 97.
No. 6). Plate IV. fig. 50. 1294-'69.
i 3 2 PRECIOUS STONES.
APOPHYLLITE.
APOPHYLLITE. Translucent, white, natural crystal, prismatic octahedron, with
basal planes ; % in. diam. ; claw mount. 1296 '69.
PYRITES.
PYRITES. Brass yellow, rose-cut ; | in. by I in. ; light coronet mount.
1335 '69.
LUMACHELLA, OR FIRE MARBLE.
LUMACHELLA. Polished, nearly flat oval ; 1 in. by f in. ; coronet mount.
123769.
MALACHITE.
MALACHITE. Opaque, bluish green ; ^ in. diam. ; convex top, coronet mount.
133469.
PEARL.
PEARL. Whole, white, secured by a pin passing through a claw on each side ;
on each shoulder of the ring mount are 2 pearl-shaped brilliants, with
3 smaller brilliants ; there are 4 other small brilliants, one at each corner
of the setting. 1337 '69.
PEARL. White, whole, short ovate ; diam. \ in. ; mount with 4 claws.
1340 '69.
PEARL. Black, whole, round ; diam. ^ in. ; plain, mount with 4 claws.
1338 '69.
PEARL. Cherry pink, whole, round ; diam. - in. ; claw mount. (Hope
catalogue, p. 10, No. 88.) 1339 '69.
There are two specimens not included in the above list. One of these has
been enumerated with the peridots, but it is apparently a tourmaline ; the other
stone, which possesses little interest or beauty, is probably obsidian.
TOURMALINE ? Dull green, en cabochon, oval ; \ in. by \ in. ; plain mount.
1299 '69.
OBSIDIAN ? Dull green, step-cut ; | in. by % in. ; wire coronet mount.
1295 '69.
INDEX.
Page
Page
Absorption spectra .
81, 93
Brilliant-cut . . .-
. 26
Adam as . . .
.67
Brilliants .
^fi
Agate . . .
. 100, 130
Bronzite ....
. 104
Alexandrite
. 90
Burmite ....
113
Almandine .
80, 126
Amazonstone .
. . 106
Amber . .
. 112
Cabochon-cut .
. 29
Amethyst
90, 102, 129
Cacholong
. 99
Amethyst, oriental .
. 66, 123
Cadmium borotung.state .
. 14
Anatase . . .
. 108
Cairngorm
101, 129
Andalusite
. . 109
Callainite ....
71
Andradite
. 85
Cameos . . .
99, 102
Antigorite ^ . ."".*
47
Carat
59
Apatite . . .
. 118
Carborundum .
. 31
Apophyllite
. 108, 132
Carbuncle
80, 126
Aquamarine
. 89, 127
Cassiterite
. 107
Artificial Stones
48, 51
Cat's eye . . 40, 104,
127, 131
Association of Gems.
. 32
Chalcedony
101, 130
Asterism .
62, 81
Chatoyancy
6,91
Avanturine Felspar .
. 101, 131
Chrysoberyl
90, 127
Avauturine Quartz .
. 100, 130
Chrysolite
. 85
Axinite
. 107
Chrysoprase
101, 130
Azure Stone
. 102, 114
Cinnamon stone
80, 126
Clotures ....
. 26
Balas ruby
. . 68
Colenso diamond
. 59
Beryl . . . ,
. 87, 127
Collet
. 27
Beryl lonite - .
. j. 92
Copal ....
. 113
Bezel . ...
. . 26
Coral ....
. 117
Black coral . . .
. 118
Cordierite
. 103
Bloodstone . .
. 101, 131
Cornelian ....
101, 131
Blue stones
24, 45
Corundum
61, 124
Boart
31, 61
Crocidolite
104. 131
Bobrovka Garnet
. 84
Cross facets
. 26
Bouteillenstein ,
. 86
Crown of a stone
, 23
PRECIOUS STONES.
Page
Page
Culet
27, 29
Hyalite .
. 99
Cymophane
90, 127
Hydrophane
. 98
Hypersthene
. 104
Delessite .
Demantoid
Dentelle . . .
Diamond . . . .
Diamonds, cut
Diamonds, engraved
. 101
.-.' . 84
. 29
8, 36, 54, 122
27, 31
. 61
Idocrase ....
Imitation stones
Indicolite ....
Interference phenomena .
lolite . . . .
. 118
51
75, 125
11
103, 131
Diamonds, famous .
57,59
Jacinth . . .
92, 95
Dichroiscope
9
Jade
. 110
Dichroite .
g . 103
Jadeite .
. 110
Diopside .
Dispersion of light .
. 108
8
Jargoon ....
Jasper ....
92, 128
101
Doublet . .
. 52
T A.
Jet .
113
Egyptian Jasper
. 101
Kunzite .
. 96
Emerald . . ..
. 88, 127
Epidote .
. 106
Labradorite
. 105
Essonite or Hessonite
80, 126
Labrador spar .
. 105
Euclase .
. 92
Lapis lazuli . . .
102, 131
Excelsior diamond .
. 59
Lazulite ....
. 72
Lozenge ....
. 26
Fashionable stones .
. . 2
Light, refraction of .
6
Felspar .
. 105
Lumachella .
114, 132
Fire-opal .
.98
Lustre t
. 21
Fluorescence .
6
Malachite ....
113
Forms of Crystals .
Fossil Turquoise
. . 70
Marcasite.
Margaritana
. Ill
. 114
Meleagrina
. 114
Garnet
78, 126
Moeha stone . .
101, 130
Girdle
. 27
Moldavite
. 86
Green stones .
23, 34
Moonstone
105, 131
Grossularite
.' . 80
Mossagate
. 101
Mussel, pearl .
. 114
Hrematite
112
Neglected Stones
. 32
Hardness .
. 11
Nephrite ....
. 110
Haiiynite .
. 102
Heavy liquids .
. 14
Obsidian ....
. 106
Heliotrope
. 101
Odontolite
. 70
Hessonite .
80, 126
Oligoclase .
106, 131
Hiddenite
. 96
Olivine ....
84, 85
Hyacinth . . - ,
92, 95
Onyx ....
101, 130
INDEX.
135
Page
*
Page
Opal.
97, 128
Sardonyx ....
101
V-T.TC*!.
Opalescence
. . 6
Serpentine
. 47
Orange stones .
23, 44
Skew Facets ...
. 26
Orthoclase
. 105
Skill Facets . . .
. 27
Oyster, pearl .
Smaragdite
. 47
Smoky Quartz . . .
. 101
Pearl
. 114, 132
Sonstadt's solution . .
. 14
Peridot .
Plasma
85, 126
. 101, 130
Specific Gravity
Specific Gravities, correcte
13,20
i . 18
Phenakite
. 91
Spessartite
83
Phosphorescence
. 97
Sphene
. 107
Premier or Cullinan
Diamond 57
Spinel
67, 123
Porcelain Jasper
. 101
Spodumene . .
. 96
Prase
. 101
Star Facets . . ,
26,27
Pyrites
Pyro-electricity
. Ill
. 78
Star-sapphire .
Step-cut . , . ,
62, 123
. 28
Pyrope
82, 126
Structure of crystals
. 21
(Quartz
99, 129
Sunstone . .
106, 131
Quartz, avanturine .
. 100
Tables . 5-7, 10-13,
20, 22-24
Quartz, rose
. 100
Table-cut . . . .
. 29
Quartz, smoky .
. 101
Tallow topped . . .
. 30
Quoins
. 26
Templets ....
. 26
Topaz . . .
72, 125
Red stones
22, 38
Tourmaline . ' .
75, 125
Refraction of light .
. 6, 24
Townshend collection
. 119
Rhodolite
. 83
Trap-cut ....
. 28
Riband Jasper .
. 101
Turquoise.
70, 124
Rock Crystal
. . 99
Rose-cut . . ,.
.29
Unio
. 114
Rose-opal .
. 98
Uvarovite
. 84
Rose-quartz
. . 99
Rubellite
75
Violet stones .
24, 46
Ruby . . " .
40, 64, 123
White stones . . .
22, 36
Sapphire .
Sapphirine Quartz .
63, 65, 123
. 101
Yellow Stones . .
24 44
Sard .
101
Zircon
92. 128
RETURN EARTH SCIENCES LIBRARY
TON* 642-2997
LOAN PERIOD 1
1 MONTH
2
3
4
5
6
ALL BOOKS MAY BE RECALLED AFTER 7 DAYS
Books needed for class reserve are subject to immediate recall
DUE AS STAMPED BELOW
MAR 2 2006
FORM NO. DD8
UNIVERSITY OF CALIFORNIA, BERKELEY
BERKELEY, CA 94720
U.C. BERKELEY LIBRARIES