MINERALOGY OF BEACH SANDS BETWEEN HALFMOON AND MONTEREY BAYS, CALIFORNIA By C. OSBORNE HUTTON School of Mineral Sciences Stanford University Special Report 59 CALIFORNIA DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO, 1959 STATE OF CALIFORNIA EDMUND G. BROWN, Governor DEPARTMENT OF NATURAL RESOURCES (DeWITT NELSON, Director DIVISION OF MINES GORDON B. OAKESHOTT, Chief Special Report 59 Price 50£ CONTENTS Page Introduction 7 Distribution and nature of sands 7 Electromagnetic fractionation 12 Mineralogy of the heavy minerals 12 Amphibole group 12 Tremolite-actinolite 12 Glaucophanic amphiboles 13 Hornblendes 13 Anatase 14 Andalusite 14 Apatite 14 Aragonite 14 Barite 14 Biotite 15 Brookite 16 Cassiterite 16 Chlorite 16 Chromite (see opaque minerals) : 16 Chrysoberyl 16 Clinozoisite-epidote 16 Composite particles 17 Corundum 17 Diamond 17 Dufrenite 17 Garnet 18 Glauconite 19 Gold 19 Leucoxenic material 19 Magnesite 19 Monazite 19 Olivine .20 Opaque constituents 20 Pumpellyite 22 Pyroxenes 23 Rutile 25 Sphene 25 Tantalite 26 Thorite, uranoan 26 Topaz 29 Tourmaline 29 Vesuvianite 30 Xenotime 30 Zircon 30 Doubtful identifications 30 Provenance 31 References 32 (3) Illustrations Page Figure 1. Index map showing localities mentioned in this report 8 Figure 2. Histograms of sands and heavy residues therein 9 Figure 3. Variation of mineral frequencies in sands from Princeton, San Mateo County, to Pacific Grove, Monterey County 11 Figure 4. Typical crystals and fragments of pyroxenes 24 Figure 5. Typical habit and form of detrital uranoan thorite 28 Table 1. Mineral frequencies 10 Table 2. Analyses of biotite 15 Table 3. Recalculation of biotite analysis 15 Table 4. Physical properties of garnet 18 Table 5. Analyses and optical properties of monazite 20 Table 6. Recalculation of analysis of Afio Nuevo Creek monazite 20 Table 7. Spectrographic analysis of Pacific Grove monazite 20 Table 8. Powder patterns of euxenite 22 Table 9. Analyses of uranoan thorite 27 Table 10. Recalculation of thorite analyses on the basis of 16 oxygen atoms per unit-cell 29 Table 11. Effect of heating on physical properties of Ano Nuevo thorite 29 Table 12. Powder pattern of uranoan thorite after being heated in air to 860° C. for 4 hours 29 Table 13. Mineral frequencies in heavy residues from brown sandstones of the Merced formation 31 (4) ABSTRACT A study has been made of the nature of the heavy mineral assemblages in beach sands on a strip of the California coast from the north end of Halfmoon Bay to Pacific Grove, south end of Monterey Bay. Although samples were collected over a three-year period and at different seasons, specimens obtained from any specific locality at differ- ent times were not found to vary significantly, one from another. The methods used in fractionation of heavy minerals from crude sands included elutriation, flotation in heavy liquids, electromagnetic and centrifuge separation and hand-picking. Electromagnetic work has provided a considerable amount of data on magnetic susceptibility of a range of minerals of known composition. In all, 35 minerals or mineral groups have been recognized by determination of physical properties and/or chemical composition. Among these, perhaps, the most interesting from a purely mineralogical point of view are cassiterite, chrysoberyl, dia- mond, dufrenite, monazite, pyroxenes and amphiboles that display most remarkable etch features, euxenite, tantalite, and uranoan thorite. Complete chemical analyses of biotite, monazite, and thorite have been made and are discussed in relation to their structural formulae and physical properties; from the Pb/Th,U ratios in monazite and thorite, tentative ages have been calculated. An age of 106 X 10 G years, approxi- mately mid-Cretaceous, has been determined for the monazite that is clearly derived from the granitic rocks at Monterey. The recognition of the nature of non-translucent mineral particles has proved diffi- cult, but magnetic fractionation has been helpful, and inspection in oblique illumina- tion with a wide field binocular microscope is absolutely necessary. Of considerable value were chromatographic techniques, use of alpha-ray track plates, and the NaF- NaoCO.j fusion mixture for detection of uranium-bearing minerals. A complete study of the problems of provinance has not been attempted at this stage, but it is pertinent to say that, in most instances, the heavy minerals in the beach sands have been derived from plutonic intrusives, sediments, and associated submarine lavas and tuffs that make up the drainage area of streams that reach the Pacific Ocean in this locality. The source of thorite, chrysoberyl, euxenite, and tantalite, all minor or rare constituents, has not been determined. (5) MINERALOGY OF BEACH SANDS BETWEEN HALFMOON AND MONTEREY BAYS, CALIFORNIA By C. Osborne Hutton INTRODUCTION This work was undertaken primarily to determine the nature of the minerals in blacksand paystreaks (concentrations of dark minerals in minor beds, lenses, or irregular layers), the composition of the heavy min- erals in average beachsands, and subsequently to deter- mine the distribution of such constituents along a section of the central California coastline. Acknowledgements. The writer would like to express appreciation for the opportunities for research provided by the Raw Materials Division, Atomic Energy Com- mission's Contract AT (30-1) -11 17, and to facilities made available by and through that organization. To Mrs. Muriel Mathez, Dr. P. Merritt and Dr. F. G. Tickell, sincere thanks are tendered for assistance in many ways at various times, and to Professor Adolf Pabst, Uni- versity of California for the X-ray diffraction pattern of euxenite. DISTRIBUTION AND NATURE OF SANDS Sands were collected from many localities between the north end of Princeton Beach, San Mateo County, Santa Cruz, Santa Cruz County, and Pacific Grove, Monterey County, at the south end of Monterey Bay (see figure 1). Forty-nine samples of blacksand paystreaks from 17 localities, and 86 typical sands from these and other localities were collected along the coastline. Blacksands are relatively numerous, nowhere show great lateral extent or depth, and in many places are only transient. Storm conditions appear to favor active concentration of the heavier constituents in these sands. However, some blacksand concentrations appear to be relatively stable. They are particularly well developed in the following localities: Princeton Beach just south of the pier, south side of the mouths of Tunitas, San Gregorio, Ano Nuevo Creeks, south of Pigeon Point Lighthouse (rocky shoreline with shallow depth of sand), several points east of Ano Nuevo Point, and at many points between Pajaro River and Moss Landing in Monterey Bay. Paystreaks that occur between the mouth of Salinas River and Monterey appear to have a stability of an intermediate character. The presence of a head- land or river effluence immediately to the north of black- sands is common and these obstructions, by altering the direction of southward-moving ocean currents, or by reducing velocity, have permitted deposition of the heav- ier part of the sedimentary load, in localities where blacksands are especially well developed, such as the mouth of Tunitas Creek, plentiful driftwood makes post-hole sampling difficult. Although grains of specific minerals may exhibit a high degree of roundness and polish, the constituents of the sands generally are angular, with quartz and feldspars particularly so. The average grain size does not vary notably from place to place and most of the sands may be classified as medium-grained or fine- grained (Wentworth, 1922). Blacksands tend to be finer grained than sands showing little accessory mineral con- centration, but the ratio of heavy minerals to light in- creases notably with decrease in grain diameter (figure 2). This is particularly evident in the very fine-grade and silt fractions, since they are made up almost en- tirely of heavy minerals, but such fractions rarely make up more than a few percent of the total sample. Where winds have selectively removed low specific gravity minerals from sand, the grain size of the thin veneer or residue of heavy constituents that remains as blacksand is very much finer than that of light-colored surrounding sand on which the winnowing process is not far advanced. Although the products of the win- nowing action of prevailing on-shore winds are quite evident at many points on the coastline they are of small volume; production of larger quantities of black- sand by these means was observed particularly in the sand-dunes both to the north and south of the mouth of Pajaro River. The relative frequencies of the heavy minerals present in a number of representative assemblages after re- moval of magnetite and ilmenite are shown in table 1 and, by and large, these data are averages of counts of at least 300 grains for each of several preparations from specific localities. For example, the data recorded under " Whitehouse Creek" have been obtained by averaging counts of a total of 400 grains in each of three size- fractions of eight samples from that locality, that were (7) CALIFORNIA DIVISION OP MINES [Special Report 59 50' 40' 3C 2C Iff 37°00' 50' 4C pt. Lobos Pt. San Ped ro 90° Bolsa Pt.> G a z o s C r. Whitehouse Cr. Ano Nuevo Pt DAVENPORT, LOCALITY MAP MOSS LANDING / Salinas R. Scale of Miles 6 4 2 10 40' Pacific Gr, ONTEREY 30' 20' 10' I22°00' 50' Figure 1. Index map of coastline from Golden Gate to Pacific Grove, Monterey peninsula, showing localities specifically mentioned in this report. 1959] MINERALOGY OF BEACH SANDS collected over a period of 2 years. But for the finest screenings of Whitehouse Creek material, — 250 mesh, fewer than 100 mineral grains remained in each case after removal of ferromagnetic (magnetite) and strong- ly paramagnetic (ilmenite) fractions; hence counts of any significance were not possible. Where at least 300 grains were available for counting, the percentages of the different minerals thus obtained have been expressed in table 1 following the procedure of Evans, Hayman, and Majeed (1934). However, where the number of particles is inadequate to permit satisfactory use of this scale the following system is used: p = predominant (> 60 percent) a = abundant (20-59 percent) fa = fairly abundant (5-19 percent) m = minor constituent (< 4 percent) r = rare. Many samples from localities other than those listed in table 1 were studied, but the grain counts from these have not been included in this table since they add little if anything to the general picture set out in table 1 and figure 3. Magnetite and ilmenite make up much of the heavy fractions and ilmenite, which tends to have larger average grain-diameters than magnetite, is the more abundant constituent in most samples. -i — I — i — I — r -i i i i — r t I i I r X A _60 _40 I TOTAL FRACTION. HEAVY RESIDUE. IOO 80 -D 20 rn O > ra 100 £ 80 CD m H 60 m m z 40 to 20 N m CO o 100 o > 80 £ 60 40 20 h. z z FlGUBE 2. Histograms of sands and heavy minerals therein. (1) Princeton Beach; (2) Mouth of Tunitas Creek; (3) Mouth of San Gregorio Creek ; (4) Mouth of Butano Creek ; (5) Mouth of Bolsa Creek ; (6) Mouth of Gazos Creek ; (7) Mouth of Whitehouse Creek; (8) Mouth of Ano Nuevo Creek; (9) Aptos Beach; (10) Mouth of Pajaro River; (11) Marina Beach; (12) Monterey; (13) Pacific Grove. 10 CALIFORNIA DIVISION OP MINES [Special Report 59 SN0I1VNIHH3130 mjianoa M Q. s o in CM 1 - u -_ -_ jr u> a> 2 in 4 o to 1 CM — — — CM — — — a» Z o to 4 CM IO 1 - 3XISI0Z - - (UN Id) . . . - - y> U- — IO IO * +■ 4- 4 1 h- h- N- (0 00 * in (i) to (£) h- ^* ^" in" CM CM *• 3NIAI10 - CM — — — CM — 3iiA00snn CM 31IZV NOW - - * * * — — — — — — — to «ar _ -_ _ - 1VIH31VH 0IN3X00H31 — CM CM — to to — 3N3HlSd3dAH -_ rt rO '— in S — "t '— CMCM — iO*l"*J- — CMtOCM — — lomioin^mmtomin — * IO — CM * * t3dM-AX0) 30N31BNH0H -— *r ■— — -— cvi — — — — — — — CM — — ST — IOCM — CM CM — CM - W H) - » * . + + — — — — — — (Oto IN MO d 8) 30N31BNdOH "— — ID — *1" If) rO — — to W-" ^-ro io-if)if) m 10 10 <» 10 — cMm^h-h- — IO — CM 1" * * (N33d0) 30N31BNdOH uj uj 1 ui + to to cm 10 to in — cm to 10 in to NIBinin-(B'f*KI*IO<0 UJ + 1 » IO K) - * B (J It 0103 i 10 3NVHd03nV13 - - -_ -_ - 31IN000V13 - - - t»Nld) 13NdV3 "— to to in _ cm -_ r- r- + — cm — — in — **■ tototo — — ** 04 — or < ^ J 0- < UJ V I 1 / A, XV Y/A ;W TT-, \\ x • / / XV^ U-/- *rV< +7^ .*K~ / < a o N "u o 0S3 - 093+511 SII+09 - 09 + ZE S3ZIS N33U0S 12 CALIFORNIA DIVISION OF MINES [Special Report 59 The li*rlit fractions, material with specific gravities less than about 2.88, consist mainly of feldspars, quartz, acid volcanic glass, glauconite (this is found in heavy fractions as well), calcite, composite rock fragments, clay pellets, micas, fragments of both calcareous and siliceous organic remains, and a minor amount of non- mineral matter. Detailed investigation of this material has not been made. Variation of mineral frequencies, exclusive of those for ilmenite and magnetite, is illustrated in figure 3 which shows the following points: (1) The effect of introduction of fine-grained augite from the Purisiraa formation. (2) Changes due to accession of material from San Lorenzo River that enters the ocean at Santa Cruz just north of Aptos. (3) Marked change of character of sands south of Salinas River. ELECTROMAGNETIC FRACTIONATION Provided the diameter of particles in samples is uni- form, the magnetic susceptibility of the particles de- pends largely on composition. Ironstain on the surface of mineral grains can have considerable effect on their behavior in a magnetic field, and on many occasions, stains on some grains and not on others have permitted selective attraction and concentration, after which the stain has been removed by chemical means. Thus it has become standard practice not to remove ironstain unless, of course, it is excessive, until the last possible moment. Artificial production and selective deposition of metallic iron films on mineral grains followed by electromagnetic fractionation has been utilized in some instances (Vin- cent, 1951, p. 1074). The Frantz separator was usually adjusted with a slope of 15° and a tilt of 10°, but before separations were made with it, ferro-magnetic material was removed with a hand electromagnet (Hutton, 1950, p. 644). The relative order of fractionation of a number of constituents with a particle size range of — 0.124 -(-0.061 mm, follows, but excluded are data on several minerals for which there was too small an amount of material for experimentation : Fraction 1. Current 0.2 amps: (a) Ilmenite, martitized magnetite, and other oxides of iron with or without titanium ; often heterogeneous in nature, (h) Iron-rich chrome spinels, (e) Silicates, chiefly pyroxenes and aniphilioles that contain inclusions of magnetite, ilmenite, etc. (d) Composite particles. (e) Iron-rich epidote and allanite (FesOs, 10.25 percent; FeO, 7.:V.'> percent; MnO, 0.74 percent; ThCK, 0.95 percent). Al- though only dubiously recognized as constituents of the sands studied, members of the colnmbite-tantalite series are attracted at about 0.25 amps. ; samarskite is attracted at approximately 0.275 amps. Fraction 2. Current at 0.35 amps: (a) Chromite. (1>) Less ilmenite than at 0.2 amps. (c) Green and brown hornblende abundant here. (d) Pyroxenes, chiefly augite and hypersthene ; olivine with 15-20 percent of the fayalite molecule. (e) Epidote, garnet (spessartite-almandine ; » = 1.70-1.80; sp. I»r. = about 4.1. chrysoberyl, presence possibly due to inclusions, and inclusion-bearing monazite. (f) Euxenite; other studies by the writer have shown that members of the euxenite-polycrase, and aeschynite-priorite groups generally, are attracted at 0.35 amps., or very close thereto, although a sample of blomstrandine from Morefjaer, Arendal, Norway was concentrated precisely at 0.31 amps. (g) Composites. Fraction 3. Current at 0.45 amps : (a) Main pyroxene concentrate (composition of the common pyroxene is approximately equivalent to that of augite close to diopside as determined from optical measurements, viz: Wo 49 percent, En 38 percent, Fs 13 percent). (b) Garnet (spessartite-almandine). (c) Hornblendes, less abundant than in the previous fraction. (d) Sphene, monazite, pumpellyite, xenotime. (e) Minor opaque minerals. (f) Zircon by reason of inclusions therein. Fraction 4. Current at 0.75 amps : (a) Main monazite and sphene fractions. Monazite contained Th0 2 4.22 percent ; FeO 0.61 percent ; sphene with AI2O3 1.44 percent and total iron as FeO 1.23 percent was at- tracted at 0.60 amps., rejected at 0.55 amps. (b) Considerable amount of uranoan thorite; dark-colored phase. (c) Garnet (grossular types). (d) Zircon by reason of inclusions. (e) Pyroxenes, amphiboles, opaques, epidotes, all in minor amount. (f) Composites abundant in specific instances (saussuritic ag- gregates, etc.). Fraction 5. Current at 1.2 amps : (a) Sphene important but less abundant than in fraction 4. (b) Zircon with minute inclusions. (c) Uranoan thorite; lighter green than previous fraction. (d) Grossular, hydrogrossular. (e) Composites very important in some samples. (f) Opaque fragments usually rare. (g) Corundum; andalusite, but erratic in behavior due to fre- quency of opaque inclusions. Fraction 6. Fraction rejected at 1.2 amps: (a) Zircon and apatite are usually the dominant constituents here. (b) Pale green uranoan thorite. (c) Rutile, brookite, anatase, cassiterite, scheelite, barite, corun- dum, diamond. MINERALOGY OF THE HEAVY MINERALS Amphibole Group At least one member of the amphibole group is pres- ent in each size fraction of each of the sands studied, although three and even four varieties have been found in many samples. Amphiboles recognized are derived from at least two distinct paragenetic associations : tremolite-actinolite and glaucophane from a metamorphic environment, and brown and oxy-types with which may possibly be grouped a green to brownish-green horn- blende, derived from volcanic, or certainly igneous sources. In general the frequency of amphiboles present in the sands shows considerable variation from north to south along the coastline studied and, in general, mem- bers of the group are only slightly more abundant in coarser than in finer grade sizes. Tremolite- Actinolite Members of this group are rare and occur as minute needle-shaped or ragged fragments of very pale green to bluish-green color with faint pleoehroism. For one sam- ple, a — 32 -f- 60 fraction from a blacksand paystreak three-quarters of a mile south of the mouth of Pajaro River, the following optical data were recorded : a= 1.627 y = 1.649 X = very pale green Z = pale bluish green Z A c = 18° 2V = 65° (-) 1959] MINERALOGY OP BEACH SANDS 13 The extinction angle Z' to c for -what seemed to be fragments resting on (110) was approximately 22°. a value in excess of that found for the (010) plane or the true extinction angle Z to c. On the basis of Fresnel's law the extinction angle for an orientation parallel to a cleavage plane when Z to c and 2V are 18° and 65° re- spectively, was found by construction (Duparc and Pearce, 1907) to be 21°. Accordingly it must be stressed that determination of extinction angles must be made with some caution when orientation within the zone [001] is not known exactly. The blue tint in the Z ■ — vibration direction suggests that this amphibole is a member of the actinolite-glaucophane series of Kunitz (1930), but close to the actinolite end since a lavender tint is not evident. Glaucophanic Amphiboles Amphiboles that belong to the glaucophane-riebeckite rather than to the actinolite-glaucophane series are fairly widely distributed but in none of the samples examined do they exceed 1 percent of any particular size fraction, and quantity is usually much less than this. An abraded, but dominantly stumpy, prismatic form is general. Pleochroism with X = colorless, flecked with green, Y = violet, and Z = deep azure blue is usual in spite of variation in other optical properties. Separation of sufficient material for more complete determination was not accomplished except once when the following data were obtained: a = 1.635 ± 0.002; y = 1.649; Y — a = 0.014; 2V = 12° (— ) ; ZAc = 4° ; dispersion r < v strong. The type of dispersion was not recognized with any degree of certainty but the positions of the colored areas in the interference figure relative to the points of the melatopes suggest dispersion of bisectrices, rather than of optic axes. The size of the optic axial angle points to a composition close to crossite, but the amphibole is not that since optic axial plane and clino- pinacoid are parallel. Optic axial angles larger than 30 to 50° appear to be more usual, however, and zoned crys- tals with lighter colored central areas and darker periph- eries are not uncommon. Inclusions are frequent and the following were rec- ognized : quartz, plagioclase (most likely albite), mem- bers of the clinozoisite-epidote group, muscovite, stilp- nomelane, sphene, pumpellyite ( ?), apatite; some opaque grains were found, enhancing the magnetic susceptibil- ity of the particles. Hornblendes Three distinct varieties of hornblende are present: green, brown, and oxy-types. In general, green varieties are dominant, and brown and oxy- forms much less abundant. Well-rounded particles are particularly com- mon in coarser grained fractions, whereas cleavage frag- ments with ragged terminations or otherwise irregularly fractured grains are decidedly dominant in the finer, and especially in the finest, grade sizes. In general terms, hornblendes are attracted at lower field strengths than are pyroxenes, particularly clino- pyroxenes, but not always, since pyroxene crystals and fragments are more often contaminated with opaque oxides than are hornblendes. This is particularly true of the - — 115 -j-250 fraction from the mouth of Gazos Creek where both clinopyroxenes and hypersthene make up approximately 50 percent of the ilmenite fraction attracted in a weak magnetic field (0.10 amps.). In ma- terial collected from a point just south of Pajaro River, both pyroxenes and amphiboles were so contaminated with inclusions of magnetite or ilmenite that they were fractionated together with magnetite in the ferromag- netic portion and also with ilmenite in a slightly stronger field. For crystals devoid of opaque ferruginous and or titaniferous inclusions, however, pyroxenes are magneti- cally less susceptible than amphiboles. In general, inclusions are less frequent in hornblendes than in pyroxenes and where identification could be made they were: iron oxides (magnetite, titanomagne- tite, ilmenite, hematite), apatite, quartz, plagioclase, leu- coxene (?), and needles of rutile (?). Solution effects have hampered development of grains with multiple terminating pyramids — the so- called "cockscomb" structures of Ross et al. (1929) and other investigators ; in fact, they are decidedly rare com- pared to similar effects produced in the associated ortho- rhombic and monoclinic pyroxenes. Green or Greenish-Brown Amphiboles. Amphiboles belonging to this category are more important constitu- ents of blacksands, paystreaks, and heavy fractions than the sum of other varieties present. In material from Princeton Beach, green or greenish-brown hornblendes constituted 60 percent of the — 60 +115 fraction, and percentages in excess of 20 are not uncommon in other samples. No size fraction of any sample studied is free from hornblende of this category. Optical properties show a range of values and the data that follow give some measure of this : Mouth of Ano f mile south of Range or other Nuevo Creek Pajaro River data noted a 1.654 1.650 1.650-1.662 7 1.672 1.665 1.665-1.679 — a 0.018 0.015 0.014-0.022 ZAc 19° 17° 14-22° X yellowish -green pale green yellow Y olive-green green brownish-green Z deep green with deep green deep brownish- a tinge of blue green (rarely nearly opaque) Absorption : Z >Y >X Z>Y>X In some instances green to greenish-brown hornblendes are so deeply colored that they are nearly opaque for the — 60 +115 size fraction, and at first sight, these grains differ little from ilmenite when they are viewed in oblique illumination. This is especially so if fragments are well rounded and polished so that prismatic cleavage is not evident. Undoubted solution effects comparable to those devel- oped in pyroxenes are infrequently found (see Princeton — 115 -|-250 mesh where incipient pyramidal termina- tions have developed). Zoning due to pre-depositional circumstances was noted in occasional grains, and gen- erally this takes the form of dark green nuclear areas with paler colored or colorless peripheral zones. Brown amphiboles, generally less abundant than are green varieties, exhibit a range of forms similar to those of the latter, and show complete gradation towards them optically. In a number of instances, as in brown varieties devoid of any reddish tints, pleochroism is not as pro- nounced as in green hornblendes. 14 CALIFORNIA DIVISION OF MINES [Special Keport 59 Oxy -Hornblendes. Red-brown amphiboles of the oxy- hornblende type are present in most size fractions but in no instance exceed 41 percent of any fraction and usually are very much less than this. They exhibit a range of forms similar to those found for green and brown amphiboles. Color is typically red-brown and op- tical data for a wide range of fragments are as follows : X = brown, yellowish-brown, golden brown. Y = deep brown. Z = deep red-brown. Z > Y > X 2V = 59 — 73° (— ) ZAc: 2 — 7°, but usually closer to the lower figure (Fedorov stage determinations). a 1.675*- 1.678 Y 1.740*- 1.747 y-a 0.062 -0.069 Anatase Anatase, recognized as a rare constituent of the finest fraction of blacksand found at the mouth of Afio Nuevo Creek, occurs as pale yellow, non-dichroic, rectangular, fractured tablets that exhibit a pattern of parallel striations. Andalusite Very well rounded (Princeton) to highly irregular grains (Whitehouse Creek) of andalusite were found in a number of samples, but this constituent is never more than a minor accessory. Inclusions are visually quite numerous, with both opaque and brownish iron oxides predominant but biotite common, whereas in other samples extensive sieving with quartz, feldspar, or bio- tite was noted. Pleochroism is pronounced and in larger sized fragments, as in the — 32 -(- 60 fraction of Tunitas Creek sand, this characteristic is most marked. For the Tunitas Creek example the following data have been determined. a = 1.633 Y = 1.644 Y — a = 0.011 X — rose Z = green Unfortunately adequate material for manganese and iron determinations was not available, but the intensity of absorption and rather higher refractive indices sug- gest some degree of replacement of Al 3+ by Mn 3+ and/or Fe 3+ . Apatite Although apatite is widely distributed, few fragments are found in most samples, and more than 0.5 percent was not recorded. Stumpy euhedral prisms that exhibit effects of slight abrasion predominate in finer grade sizes, whereas well rounded fragments are most often met with in coarser screenings. In many cases apatite is free from inclusions, but when these are seen they are usually in the form of lines of cryptocrystalline particles arranged parallel to * These values, 0.003, were found for a large number of oxy- type amphiboles pr< s< nt in the sands. the vertical crystallographic axis. Such crystals have the appearance of being medium to strongly dichroic in smoky or brown tints, but to what extent this appar- ent dichroism results from a "wink" effect due to rapid change of the difference of refractive indices between inclusions and apatite host on rotation of the microscope stage, is not clear. Pale yellow apatite is associated with colorless frag- ments of the same mineral in one sample (mouth of Aiio Nuevo Creek), and in a black sand paystreak from the northern end of Princeton Beach, occasional extraor- dinarily smoothed, egg-shaped grains were recognized. The latter are colorless and water-clear with the longer dimension of the ellipsoidal particle invariably at an angle to the c crystallographic axis, that is, to the longer dimension of the original crystal. Such material must result from very long-continued abrasion of initially irregularly shaped fragments, otherwise it is difficult to visualize the way in which crystals of apatite of normal habit could become worn to elliptical forms that do not exhibit some degree of parallelism to the forms of the original crystals. These circumstances are reminiscent of those described for zircon from Slab Hut Dredge, Westland, New Zealand (Hutton, 1950, p. 687). Collophanic fragments derived from tooth and bone material are generally irregular in shape in finer grade sizes and rounded or much abraded in coarser par- ticles; color is typically pale yellow but shows a range between this and red-brown. Weak anisotropism and cryptocrystalline aggregate structure that does not exhibit definite extinction, are characteristic. X-ray powder patterns are yielded by single particles of collophane, and although films exhibit no reflections at angles greater than 60° 2 0, the patterns are otherwise comparable to those of apatite. Measurements in one case gave cell dimensions of a = 9.33 A., c = 6.88 A ± 0.03 A, or values similar to those recorded for carbonatian fluor- apatite. Aragonito The orthorhombic form of calcium carbonate has been recognized as an occasional constituent of sands from several localities, and in each instance it forms thin, abraded fragments with aggregate structure ; presumably this is shell material. A distinct pleochroism, nearly colorless to pale mauve or purple (Hutton, 1945, p. 300) is usual; however, optic axial angle determinations of 17° and 19° in two fragments with y = 1-684 and 1.685 respectively, support diagnosis as aragonite. If this is shell-derived material, and it certainly appears to be so, the data recorded here do not support B0ggild's (1930, p. 237) contention that the optical properties of shell aragonite are not exactly identical with those of aragonite from other natural sources. Barite Barite was found in four samples but only in sands near the mouth of Pajaro River is it more than a min- eralogical curiosity. Rectangular cleavage fragments of dusty aspect due to clouds of innumerable minute, and colorless indeterminate inclusions are usual. A mottled or blotchy effect comparable to that found in barite of concretions is evident between crossed nicols in some instances; it may result from slight disorientation of 1959] MINERALOGY originally parallel lamellae. An optic axial angle of 38-40° and a value of 1.635 for a supports the conclu- sion that the mineral has a composition close to that of pure harium sulfate. Biotite It is to be expected that micas would not be well represented in mineral assemblages on exposed ocean it- beaches but biotite has been recognized in four sands, in which it is usually more abundant in the coarser size fractions. A deep red-brown color with very strong pleochroism is characteristic and, for separated platelets, the following data have been determined : Aptos Beach : y. 1.656, 1.662, 1.664, 2V: 0° 0° 34° Dispersion- - r 2 34.9S 1.105 2.689, , M1 I 4.00 ma), 17.06 .502 1.544] '■;";' Ti() 2 3.47 .087 .200 <■ — 1 "l Fe 2 O s 9.30 .175 .536 ' FeO 14.49 .202 .931 2.591 MnO 0.42 .006 .027 MgO 5.SO .144 .004 CaO 0.38 .007 .031 Xa 2 0.39 .006 .058 K2O 7.02 .074 .688 ILO 3.96 .220 2.030 / o 144 F 0.47 .012 .114 \ This leads to the formula : (OH,F),. 14 (K,Na,Ca). 7S (Mg,Mn,Fe 2 +,Fe 3+ ,Al,Ti)o , [(Si,Al)40 1? ] enter the tetrahedrally linked sheets, the remainder in six-coordination. The question of the position of Ti 4+ can- not be unambiguously settled here, but it should be re- membered that similar difficulties arise in distribution of Ti 4+ in titaniferous augites low in Fe 3+ and Al 3+ . In such cases where the combined Si 4t and Al 3+ is insufficient to satisfy the requirements of pyroxene structure, there ap- pears to be no alternative but that Ti 4+ may replace Si 4 * (Dixon and Kennedy, 1933; Deer and Wager, 1938). If Ti 4+ is grouped with the cations of coordination number 6, then Al 3+ in the Pacific Grove biotite is domi- nantly tetrahedrally linked with only a small amount remaining to replace X and Y group cations. This divi- sion of Al 3+ is found in biotites from igneous rocks de- void of muscovite in which biotite tends to be the sole mafic constituent or those in which minor hornblende may also be present (Nockolds, 1947). Certainly the granites which crop out in the vicinity, the source rocks of the mica described here, may be so described, in that they are generally devoid of muscovite and hornblende. The figure of 0.78 for the large ions Ca 2+ , Na + , and K + is unsatisfactory and suggests that the analytical deter- mination of alkalis may be in error. On the other hand, the relatively high figure for H 2 — 105° C. would tend to suggest that the mica has undergone some alteration ; this may also be a reason for the deficiency in the \V — group. Spectrographic determinations on the Monterey biotite are as follows: >10 percent Al, Fe, Mg, Si 1-10 Ti 0.1-1.0 Ca, K(?), Mn, Na 0.01-0.1 Ba, Pb, Zn 0.001-0.01 B, Cu, V <0.00i Ag, Cr, Mo, Sn Not detected As, Bi, Cd, Co, Ga, Ge, In, Ni, P, Pt, Sb, Ta, Th, U, W, Y, Zr. Physical properties for the analyzed biotite are : a = 1.610 ± 6.004 Y = 1.665 ± 0.002 Y-a = 0.055 X = yellow Y = Z dark brown X< Y = Z 16 CALIFORNIA DIVISION OF MINES [Special Report 59 Dispersion strong with r < v. 2V = — 20° ; generally 8 — 12°. sp. gr. at 22°C. 3.04 — 3.09 ; generally 3.06 0.01 Brookite Brookite is a rare but fairly constant constituent of finer fractions of many sands, and is almost invariably found concentrated in the non-magnetic fraction * as- sociated with zircon, cassiterite, apatite, rutile, etc. It forms equidimensional sub-euhedral to euhedral grains that appear to be tabular parallel to (010), since a high proportion of grains exhibit Z perpendicular thereto (Palache et al. 1946, p. 560). Color by trans- mitted light is pale yellow, but in oblique illumination it is brownish-yellow with a rather waxy or greasy luster (cf. rutile). Pleochroism is faint but distinct for orienta- tion perpendicular to Z, with the direction perpendicular to the striae pale yellow, and yellow parallel thereto. In blue light 2V is small and the optic axial plane is parallel to the striae, whereas in red light 2V is dis- tinctly larger and the optic axial plane is perpendicular to the c axis, assuming that the striae are parallel to that axis. Cassiterite Cassiterite has been recognized with certainty in the finer fractions of samples from Aptos Beach and the mouth of Ano Nuevo Creek, as anhedral particles of highly irregular shapes and pronounced conchoidal fractures. Brown grains, with blotchy distribution of color and weak dichroism are usual but here and there fragments that give positive tests for tantalum with tannin, and exhibit strong dichroism, colorless (O) to deep blood-red (E), were found. Some twinning was de- veloped, and in such fragments dichroism is much more evident, owing to juxtaposition of two distinct tints across the composition plane. Chlorite Chlorite was recorded as a rare accessory in three examples and it is to be expected that individual flakes of members of this group, as distinct from composite grains containing chlorites, such as saussurite, schist fragments, etc., would be poorly represented in sands on open beaches. From the finest fraction of sand from the mouth of Gazos Creek occasional ilakelets of pale green, optically negative, chlorite were separated and determined to have refractive indices very slightly less than 1.64, but this figure was not accurately determined owing to lack of material; however, one of the iron-rich chlorites appears to be indicated. Chromite Chromite and chromian spinels will be considered under the heading of opaque minerals. Chrysoberyl Sonic of the occasional colorless fragments of chryso- beryl noted in the assemblages of sands from near the mouth of Ano Xuevo and Butano Creeks were well anded, others irregular with conchoidal fractures, and her water-clear or semi-translucent owing to myriads of l: '' '' ! amps, when the isodynamic separator is set at a slope of 10° ar tilt of 8°. dust-like inclusions. Rare fragments exhibit repeated twinning with well marked striations parallel to the periphery * ; for such crystals the following data were Foiind: a = 1.739 ± 0.003, y = 1.747, y — a = 0.008. These refractive indices are distinctly lower than those recorded for chrysoberyl by Winched (1951, p. 89), but somewhat higher than data obtained for synthetic chrysoberyl by Geller (1941, p. 564), viz. a = 1.732, Y = 1.741. In a fragment of a multiply twinned crystal the optic axial angle ranged from 40-55° (-)-), whereas in other particles 45-60° ( + ) was noted. Clinozoisite- Epidote Members of the epidote group are widely represented and the Al-Fe members of the epidote series are particu- larly common, with piedmontite rare. Zoisite is a minor constituent but widely distributed, whereas allanite, the only member of the allanite series recorded, is un- common. Epidote Series. Epidote and clinozoisite are grouped together, owing to the difficulty of distinguishing be- tween them when the composition is close to that of non- ferriferous members, without recourse to time-consum- ing refractive index determinations. Distinction is also rendered more troublesome by notable and rapid move- ment of the ellipsoid, movement that does not seem to be entirely dependent on compositional change, (Johnson, 1949, pp. 506-515).- Clinozoisite-epidote is ubiquitous in each size fraction with slightly greater frequency in finer grade sizes. Fragments are mainly anhedral and conchoidally frac- tured, colorless with slate blue anomalous tints in the finest size, but pale yellow to greenish yellow with high order colors in coarser fragments. Pleochroism is often evident in particles of large size, or in iron-rich varie- ties. Refractive indices for the Y-vibration direction lie between 1.740-1.752 in fragments tested; this is equiva- lent to approximately 8-12'/' of Fe 2 3 in the molecule. In the — 60 -f- 115 fraction of material from near the mouth of Whitehouse Creek, however, rounded cleavage fragments of clinozoisite were found with faint, but striking pleochroism, X = pale yellow, Y = pale blue, Z = pale yellow, Y > X = Z. These characteristics are suggestive of pumpellyite, but other optical data (cf. Johnson, 1949, Table 4, p. 514, last column), defi- nitely point to clinozoisite; these are: a = 1.720, £=1.724, y = 1.735, y — « = 0.015, 2V = 90° (±), r < v distinct. Inclusions are frequent and clouds of dust-like parti- cles of iron oxides are particularly well represented in clinozoisitic or iron-poor varieties. Zoisite. The orthorhombic dimorph of clinozoisite is rather widely distributed as clear colorless anhedra with occasional inclusions of opaque oxides. These fragments often show preferred orientation in mounting media so that centered or very nearly centered interference figures may be obtained therefrom. a - zoisite, much less common than the (5 - variety, is recognized by parallelism of the optic axial plane and (010) cleavage, and by strong dispersion with r < v * Comparable, to some extent, to the crystals figured by Berthois (1935), pi. 4, tigs. 1 and 2). 1959" MINERALOGY OF REACH SANDS 17 (Bolsa Point material). The |3 - variety shows ;i range of 2V (0-20°) will) r > v. When 2V is very small, the mineral is almost uniaxial in bine light but in red light the optic plane is perpendicular to the cleavage (Princeton Beach). Allanitc: Occasional fragments of non-metamict al- lanite were fonnd in several beach sands, but never did it exceed 0.5 percent of any size fraction. The habit ranges from well-rounded almost spherical forms to sharply angular fragments with pronounced conehoidal fracture surfaces. Prismatic crystals are not common, but in the few instances where such forms could be recognized, the longer dimension was determined to be parallel to the Y vibration direction. In each instance color is characteristically a deep brown and pleochroism is intense as follows: X = pale yellow, golden yellow (in thin edges) to pale yellowish brown ; Z = very deep brown ; almost opaque. A negative optic sign was definitely determined in two instances (A no Nnevo, Butano), and a positive sign observed for material in the — 60 -\- 115 fraction of sand from the mouth of San Gregorio Creek. The size of 2V was not readily estimated due partly to intense color but for grains from near the mouth of Butano Creek a very small angle, approximately 10-20°, was noted and very pronounced dispersion was apparent. The following data were determined for two separate occurrences : Aiio Nuevo Creek Butano Creek u = 1.785 1.780 Y = 1.816 1.812 Y-ot = 0.031 0.032 Sp. Gr. (22° C.) = 3.89 ± 0.02 3.90 ± 0.02 Both samples are readily soluble in hot concentrated IIC1, and oxidation of nitric acid solutions by bismuth- ate indicated the presence of considerable manganese (cf. allanite from Yosemite National Park, California, Hut- ton, 1951). Piedmontite: A few prismatic, pale-colored frag- ments of the manganiferous epidote, piedmontite, were recognized in material from near the mouth of Aho Nuevo Creek, but elsewhere the grains are parti-colored with pronounced zonary bands parallel to the length of the fragments, that is, parallel to the 1) crystallographic axis. Pleochroism is weak but distinct as follows : X = pale yellow Y = pale purple Z = violet Z ^ X ^ Y. Birefringence, and refractive index for the Y-vibra- tion direction, are approximately 0.015 and 1.725 respec- tively. These data taken together with the relatively weak absorption suggest a variety low in both Fe 3+ and Mn 3t . Composite Particles Rock fragments and other mineral aggregates are present in every sample so far studied, and in coarser screenings they often rank among the more important constituents and in some fractions as dominant ones. No attempt has been made here to differentiate between distinct varieties of composite material for counting pur- poses, but instead any detailed identification has been made for the sole purpose of elucidating provinance. The following mineral associations and rocks con- stitute the bulk of the heterogeneous material: (1) Very fine-grained quartz-elinossoisite (or epidote) aggregates with distinctive white porcellaneous aspect in oblique illumination, and semi-translucent appearance in transmitted light. (2) Excessively fine-grained semi-opaque particles that are white, cream, or grey in color and have a polished ceramic-like appearance in oblique illumination. Quantitatively it can be shown that these consist chiefly of Si0 2 , AUOa, Ti0 2 , and H,(), and therefore they are thought to be aggregates of clays and leucoxenic materials ( rutile or nnatase). (3) Fragments of saussuritic material or quartz-feldspar- epidote aggregates; some carbonates may be present. Particles are usually well rounded, with smooth surfaces and cream to pale yellowish mottled coloration in oblique illumination. (4) Aggregates of very fine-grained glaucophanic amphiboles and epidote; greenish hornblende is sometimes present instead of glau- eophane. (5) Deep green, well rounded pumpellyite-plagioclase ag- gregates; in some instances chlorites are present. Also rounded, almost spherical grains of deep green color composed solely of ag- gregated needles of pumpellyite. (6) Epidote or clinozoisite aggregates that are pale green in oblique illumination. (7) Fragments of slightly altered andesite or basaltic rocks, the individual constituents of which can be readily identified in the powder obtained by crushing these composite particles in ap- propriate refractive index liquids. Corundum Occasional grains of corundum have been recognized as rounded, sometimes chipped, anhedra that are color- less or very pale blue, often with irregular distribution of color. The frequency with which centered interference figures were obtained suggests development of basal parting. Diamond Diamond is a mineralogical curiosity in two samples, and in one of them — sand from a point 220 yards north of Bolsa Point — constituted 17 percent of the finest fraction.* Characteristically it takes the form of highly irregular fragments with most pronounced con- ehoidal fractures, or as cleavage fragments of triangular outline. These particles have been referred to as dia- mond on the basis of the following tests : (1) The material is quite unaffected by ten minutes immersion in molten potassium pyrosulfate. (2) Specific gravities of two fragments were found to be very close to that of Clerici solution of density 3.5. (3) Refractive index is approximately equal to that of a selenium — sulfur glass in which the ratio of Se :S is 3:1. (4) The fragments are completely isotropic with a distinctive white glimmer when viewed between crossed nicols ; quite clearly the glimmer is not weak double refraction since illumination and darkness were not reproducible for 90° rotations of the stage, but this illumination could be completely reduced by preventing any incident light from above from reaching the fragments of diamond. Presumably then, the excessively high refractive index and extreme angularity of the mineral permitted much obliquely incident, yet weak light, to be reflected and refracted into the axis of the microscope. Dufrenite The occasional recognition of soft minerals in beach sands, such as those of the dufrenite group, was unex- pected and therefore some pains were taken to check the identity of the mineral in question. * This fraction amounted to 0.03 percent of the original sand. CALIFORNIA DIVISION OF JUNES [Special Report 59 Tabular, irregularly shaped fragments have a singu- lar aspecl due to anomalous interference tints and com- plete absence of extinction, while pronounced preferred orientation of grains provides more or less centered, strongly dispersed acute bisectrix figures. The following optical properties have been determined for material in sands from near the mouth of Afio Nuevo Creek: a = 1.79-2 ± 0.003, fi = 1.800, y = 1.845, y — a = 0.053, 2V = 35 — 40° ( + ) ; dispersion is very strong with r > v ; X = bluish green, Y = green, Z = deep brown. Absorption for Z is barely greater than that for Y, but is distinctly greater than for X. These refractive indices are somewhat less than those determined for carefully verified varieties of the dufre- nite-rockbridgeite group (Frondel, 1949), or for fronde- lite and members of the frondelite-rockbridgeite series (Lindberg, 1949), but higher than those for beraunite, a dufrenite-like mineral with large optic axial angle and distinctive pleochroism (Frondel, 1949, pp. 536-539). In the absence of X-ray powder patterns, however, any at- tempt to be more specific, other than listing the mineral as a member of the dufrenite group, is inadvisable. Garnet Garnet has been recognized in almost every size frac- tion of every sample that has been studied carefully, and three distinct varieties of garnet have been deter- mined — grossular and hydrogrossular, spessartite-alman- dine, and very rare uvarovite. Grossular and Hydrogrossular. Grossular is invari- ably found in forms ranging from well rounded to con- choidally bounded fragments, that are either strictly isotropic or exhibit marked but weak birefringence. Many fragments are dusted through with fine ferriferous inclusions that considerably enhance their magnetic sus- ceptibility, whereas others enclose bands of irregularly shaped colorless isotropic, unidentified particles of low refractive index, relative to that of the host. Occasional grains exhibit features, similar to those produced by repeated twinning, that may have been caused by defor- mation. A refractive index of approximately 1.742 was deter- mined for a number of fragments but in one determina- tion fragments with a specific gravity 3.45 gave a low refractive index value of 1.728; for this material posi- tive biaxial figures with 2V = 10-15° were obtained. These data are suggestive of a garnetoid such as hydro- grossular (Hutton, 1943). Such fragments do not show evidence of solution but absence of reports of hydro- grossular in sediments is interesting especially when the work of Flint and Wells (1941) is taken into considera- tion. These authors have shown that tricalcium alumi- nate hexahydrate is unstable in solutions that contain Na 2 S0 4 when it may be replaced by the "high-sulfate form" of calcium sulfoaluminate. If, on the other hand, the aluminate contains some silica as in hydro- grossular, or Feo0 3 , the stability is enormously increased. Unfortunately tl e stability of grossular compared with that of a hydro- a rnet like plazolite was not studied, but i he lack of occurrences of hydrogrossular as a constitu- nt of sediments and its rarity otherwise, may be con- nect* 1 with a decrease in stability of members of the tri- calcium aluminate hexahydrate-grossular system with Table !). Physical properties of garnet. Refractive Locality Color index Remarks Small bay, 440 yards Pale red 1.809 W. of mouth of Whitehouse Creek Pale pink with 1.799 Contained inclusions of paler periph- gas. ery Very palest pink 1.795 Salmon pink 1 .795 Colorless needlelike in- clusions. R. I. > gar- net. Pale brown 1 center 1.794 I Zoned crystal Paler brown periphery 1.797 J Very palest pink 1.789 Almost color- 1.790 less Almost color- 1.792 less Very pale brown- 1.789 ish pink Deep red 1.810 Regular skeletal ar- rangements of rutile needles. Brown 1.809 Very pale pink 1.788 Mouth of Gazos Very pale pink 1 . 794 Sp. Gr.=3.97 Creek Deep salmon pink 1.801 Sp. Gr.=4.10 Mouth of Ano Nuevo Colorless 1.760 Possibly high in gros- Creek sular molecule. Deep pink 1.795-1.800 Colorless 1.770-1.780 2V = 30-40° ( + ) Y -a = 0.003; possibly close to grossular. increase in water percentage. Thus a low-silica form of hydrogarnet in a sediment, or associated with gabbroic or ultrabasie rocks may perhaps be removed relatively rapidly in solution, or alternatively converted to the more stable grossular bv reaction with siliceous material (Flint and Wells, 1941, pp. 177-8). In material from the mouth of Ano Nuevo Creek, rounded fragments with the following rather distinctive properties were found : refractive indices ranged from 1.770-1.780 with birefringence not in excess of 0.003- 0.004 ; good biaxial interference figures ; 2V = 30-40° (-{-) ; and in one fragment myriads of transparent color- less, unidentified needles intersecting at about 60° are arranged in skeletal fashion. With the small amount of material available Ca 2+ , Al 3+ , Fe s+ , and Si 4t were found. The optical and chemical data suggest a member of the grossular-andradite series, close to the grossular end. Spessartite-Almandine. Garnet that ranges in color from nearly colorless through pale pink, and deep salmon to brown is believed to be spessartite-almandine; it is found in almost all samples and exhibits a wide variety of grain shapes. Well rounded or sharply angular fragments are general, particularly so in fractions of larger grain-sizes, although there is every gradation be- tween such forms and eubedra that display dominance of d {110}, with n {211} less often developed. In the — 60 -)- 115 fraction of material from the mouth of Gazos Creek very occasional crystals were, seen with a {100} dominant, the corners of which are slightly modi- fied, possibly by development of o {111}, but some degree of abrasion makes definite recognition of the modifica- tion uncertain. 1959] MINERALOGY OF BEACH SANDS 19 Refractive index and specific gravity determinations for a number of examples are set out in table 4 with some additional information. Zoning is frequently devel- oped but, generally, it was impossible to measure accu- rately refractive indices of different zones, except in a case when this property showed insignificant range. In many instances between the outer border of the homo- geneous central area and the outer border of the grain itself, numerous hair-like, concentric zones were seen, which were made obvious only by distinct differences in refractive index between adjoining zones. Vvarovite. Occasional subrounded grains with n = 1.83 and specific gravity = 3.85, found in material from near the mouth of Pajaro River and elsewhere, have been identified as uvarovite. Heating had no effect on these properties (compare gadolinite). Glauconite Glauconite is uncommon and its presence in heavy residues appears to result from admixture with minute opaque grains, presumably an oxide or hydroxide of iron, which confers upon the glauconite pellets a specific gravity that is higher than normal and a greater than average magnetic susceptibility. Gold Gold has been detected with certainty in only the finest fraction of material from the mouth of Gazos Creek where it ranks as one of the more plentiful con- stituents of the mineral assemblage. Nevertheless since the finest fraction constitutes only 0.56 percent of the total unfractionated sample, gold is of less importance in this sand than it would appear to be at first sight. The metal is found as paper-thin irregular fiakelets of characteristic color that are soluble in neither con- centrated HN0 3 nor II CI; a solution of the metal gave a brownish-red crystalline precipitate with pyridine in hydrobromic acid. Leucoxenic Material Leucoxene, recognized in many sands, does not consti- tuate more than 3 percent of any size fraction. It occurs as sub-rounded to rounded pellets that are semi-translu- cent, buff to white in transmitted light but porcellanous in oblique illumination ; high refractive index and bire- fringence are general and a specific gravity of 3.9 ± 0.1 at 20°C. was determined for a few fragments. Inade- quacy of material prevented determination of actual composition beyond showing that Ti 4+ appeared to be the main constituent. X-ray diffraction powder patterns yielded by three typical particles correspond exactly in d-spacings and intensities to those expected for anatase. Furthermore, the specimens prepared for diffraction consisted of parti- cles 0.05-0.1 mm in diameter — not powdered material — and in spite of this, the films exhibited perfect powder arcs without any trace of spottiness. On the other hand, no indications of line broadening are evident. Accord- ingly, the range of diameters of crystallites within each of the particles mounted for X-ray diffraction must be approximately 10 ;) to 5 X 10 : ' cm. These data demonstrate once more that much leucox- ene is anatase (Tyler and Marsden, 1938; Hutton, 1950; Broughton et al. 1950). Magnesite Colorless rhombohedral cleavage fragments of mag- nesite were recognized in the — 32 -)-60 fraction of mate- rial from the mouth of San Gregorio Creek. The parti- cles, soluble with effervescence in boiling concentrated hydrochloric acid, have the following refractive indices: n E — 1.514; n — 1.706; n -- n E — 0.192. These data indicate a composition close to that of breunnerite. Monazite The cerium phosphate, monazite, has been recognized in many samples as subeuhedral tablets flattened parallel to a {100}. Fragments of similar habit but sharply bounded by (001) and (010) cleavage surfaces also occur, together with occasional basal cleavage fragments which are easily recognized, owing to low birefringence and nearly centered acute bisectrix interference figures. In thin sections of monazite concentrates embedded in plastic, cleavage planes are much more obvious and in some instances the (010) cleavage is distinctly better developed than that parallel to (100) ; the identity of each of these cleavage directions may be fixed by its position relative to that of the optic axial plane. Inclusions are not abundant but give to otherwise clear grains a dusty aspect when viewed at low magnifications. The following occluded substances have been observed: (1) Brown semi-opaque material without definite outline, and irregularly distributed. This may he penetrative iron-stain since it is readily removed by acid treatment of more or less finely crushed crystals. (2) Aggregates of semi-opaque, isotropic particles of various shades of dark brown ; these are unidentified. (3) Colorless acicular crystals with very much lower refrac- tive indices than those of the host itself. These may be apatite, since a centrifuged fraction obtained from crushed monazite con- tained this mineral. A number of these needle-like crystals asso- ciated with the brown aggregates show some degree of parallelism In the vertical cleavage. (4) Brown colored zones at the center of crystals from which radiate out a few irregular cracks. (5) Opaque iron oxides that increase the magnetic susceptibility of the host. Monazite, from blacksands immediately south of the mouth of Auo Nuevo Creek and from white beach sands at Pacific Grove, has been separated in the pure state, first by screening — since it is largely concentrated in the finer size fractions — followed by repeated electromag- netic fractionation, and finally by hand-picking with a very fine-pointed dissecting needle. Analyses of these minerals are shown in table 5 along with determinations of physical data. The two monazites are similar chemically and optically and attention may be drawn to the following : (1) Replacement of Ce 3+ et al. by Th <+ is quite small in each case and the upset in electrical neutrality is reasonably well bal- anced by substitution of 1 ,5+ by Si** in tetrahedral coordination. This is clearly seen in Table 6 where recalculation of analysis no. 2, table 5 on the basis of 10 oxygen atoms to the unit cell is shown. There is very slight overall departure from the theoretical ratio for rare earths to P2O5, but, since the sample prepared for analysis was purified with the greatest care and inclusion-bearing crystals had been removed, no explanation except inaccuracies in analytical procedure can be offered now to account for this. (2) An appreciable amount of copper is present in the Ano Nuevo mineral, but it is not clear whether this may or may not be an abnormal feature, since comparative data are unavailable. In uranoan thorite associated with this particular monazite, however, analysis shows that 0.11 percent of (JuO is present. 20 CALIFORNIA DIVISION OP MINES [Special Report 59 Tabic 5. Analyses and optical properties of monazi 1 Cp,Os etc 64.8 YaOs see footnote ThO-> 3.49 Uo0 8 0.25 Fe 2 3 0.11 A1=0 3 nt.dt. Ti0 2 0.04 MnO nt.dt. Cu 0.007 Pb 0.018 CaO 0.47 MgO nt.dt. P 2 5 28.37 Si0 2 0.81 H 2 — 1 H.O + \ 0.3G 98.715 tc. 2 63.9 1.1 3.9 0.2 0.2 0.15 0.04 trace 0.09 (CuO) < 0.01 0.7 0.1 28.5 0.9 0.15 nil(V) 99.84 U 0.21 Th 3.067 Pb 0.018 Age 106 X 10° years * a 1.787 ± 0.002 7 1.840 y — a 0.053 2V 13° ± 2° Specific gravity at 22° C 5.21 ± 0.02 Dispersion r < v, distinct 1. 1.788 ± 0.002 1.842 0.054 13° ± 2° 5.21 ± 0.02 r < v, distinct Monazite from sands, Del Monte Properties, Pacific Grove, Monterey County, Cali- fornia. In addition, the analyst reports as follows: Zr probably <0.01 percent; Cb-Ta not detected; yttrium group 0.5-1.0 percent; U3US was determined colorimet- rically to be 0.25 percent and polarographically 0.24 percent; both Pb and Cu were determined polarographically. Analyst: Atomic Energy Commission Chemical Labora- tory Analysis 4453-B. 2. Monazite separated from blacksand paystreaks situated at storm level on beach immediately south of the mouth of Ano Nuevo Creek. No reaction for Ta or Co was obtained with tannin. Analyst: C. Osborne Hutton. •Curtis, Evernden, and Lipson (1958, p. 9), who employed the potassium-argon method, have determined the ag-es of the Montara quartz diorite and the Santa Lucia granodiorite to be 91.6 X 10° and 81.6 X 10" years respectively. Table 6. Recalculation of analysis of Ano Nuevo Creek monazite. Ce 2 3 Y0O3 — ThO,. 3.9 Fe 2 3 ALOa CaO MgO 1M ), Si0 2 Wt.%* Oxygens Hfetals 63.9 .5862 3.7081 1.1 .0144 .091 3.9 .0294 .139 0.2 .0036 .022 0.15 .0042 .025 0.7 .0125 .118 0.1 .0023 .023 28.5 1.0035 3.808 0.9 .0300 .142 ( 4.12 3.95 * U, Ti, and Cu are omitted since the amounts of each are of lit- tle significance. A spectrograph^ analysis of the Pacific Grove ma- terial made by the Atomic Energy Commission chemical laboratory is set out in table 7. Table 7. Spectrographs analysis of Pacific drove monazite. >10 percent 1-10 percent 0.1-1.0 percent 0.01-0.1 percent 0.001-0.01 percent <0.001 percent not detected Ce, La, P. Si, Th, Y, Zr.* Ca, Yb (?). Al, Mg. Fe, Pb. Cu. Ag, As, B, Ba, Bi, Cd, Co, Cr, Ga, Ge, In, Mn, Mo, Ni, Pt, Sb, Sn, Ta, Ti, U, V, W, Zn. ♦The Zr content was estimated but could not be determined accurately. Olivine A small number of anhedral and conchoidally fractured grains of olivine, free from serpentinization, has been found in a few samples. The fragments of this mineral . ■ similar to those of colorless diopsidic augite but were distinguished therefrom by the lower refractive indices, higher birefringence, and larger optic axial angle of the former. Opaque Constituents * Non-translucent mineral grains are usually the dom- inant constituents of the paystreaks and heavy mineral fractions studied aiul in the majority of sands are most plentiful in the — 115 +250 size fractions. Particles range from sharply euhedral to most irregularly or con- choidally rounded forms. It has been stressed elsewhere (Hutton, 1950, p. 670) that the difficulties involved in rapidly and positively identifying opaque or semi- opaque fragments are considerable, and little progress has been made in devising new methods or techniques that might expedite such work. It has been found useful, however, to separate opaque or semi-translucent ma- terial into fractions carefully by electromagnetic means. In general this will segregate magnetite, titanomagne- tite, ilmenite, chromite, martite, hematite, galena, and so on, but with some of these recognizable constituents are others that, although not satisfactorily identified, will be described in the hope that others may find use for the data. In addition to wide field, binocular microscopic meth- ods, and oblique illumination by white or ultraviolet light of approximately 2540A and 3660A wavelengths, the following three techniques were used : (1) In chromatographic methods, if a small quantity of undetermined fragmentary material is mixed in plastic or bakelite and a polished surface prepared, this surface when placed in close contact with a thin gelatin- coated layer ** that has been saturated with appropriate reagents will develop colored areas in those parts of the gelatin surfaces that immediately adjoin the reacting mineral surfaces. For instance, the presence of titanium may be verified in magnetite by pressing a polished sur- face, as prepared above, against a gelatin surface that has been saturated with 5 percent solution of chroma- tropic acid to which some sulfuric or hydrochloric acid has been added. If titanium is present, a reddish-brown coloration will develop. The effect of iron may be sup- pressed by addition of stannous chloride or phosphoric acid. Alternatively, fine fragments may be scattered care- fully and evenly on chemically treated gelatin-coated surfaces backed by paper ; in this case rings or haloes of reaction are produced surrounding each reacting frag- ment. The polished surface used for the detection of titanium may now be used to determine whether vana- dium is present in the magnetite by placing the polished surface in contact with a gelatin layer saturated with tannin and dilute hydrochloric acid; iron may be sup- pressed with phosphoric acid as before. This technique follows, in the main, the chromato- graphic print methods set out by Gutzeit (1942), and elaborated later by Williams and Nakhla (1951) and can be successfully employed only with minerals that are not * Owing to opacity of many minerals except in thinnest splinters, diagnosis and grain-counting may not always be correct, and the figures given in the "Opaque grains" column in table 1 may include chromite, even though a separate figure is quoted for that mineral. Thus, in making comparisons between sands the reader may prefer to combine the figures given for "Chromite" and "Opaque grains". Figures in the "Opaque grains" column exclude both magnetite and ilmenite. ** The writer has employed gelatin-coated glass and paper, which may be prepared from standard unexposed photographic negatives and printing paper by removing silver in sodium thiosulphate and then washing thoroughly. 1959] MINERALOGY OP BEACH SANDS 21 unduly resistant to reaction with the usual attacking reagents— KCN, NH 4 OH, HC1, HN0 3) H 2 S0 4 , etc. Since particles in a plastic mount are separated from each other, there is no electrical conductivity between them and hence, and unfortunately, electrographic procedures are not particularly applicable in these cases, unless of course, large enough fragments are available. (2) It is of great assistance if one is able to differen- tiate between grains that are radioactive and those that are not, or at least to know that specific fragments do not affect a photographic emulsion after a reasonable period, say twenty-four hours, has elapsed. For this purpose particles to be tested are partially embedded in the softened emulsion of nuclear track plates, Kodak's types NTA or NTB have been used, the plates set aside for twenty-four hours, and finally developed, fixed and washed. If some care is taken in the latter process, the fragments will be retained in the places into which they were originally set, so that the plate with fragments attached may be studied beneath binocular or polarizing microscope. Following this, any particular fragment may be removed from the emulsion if additional determina- tions are to be made with it. (3) In the fluoride-flux method, if mineral grains are placed on the surface of a thin cake prepared first by fusing K 2 C0 3 , NasCO.s and NaF together on a platinum or nickel crucible lid (Bowie, 1949) and allowed to solidify, momentary remelting of this cake will allow incipient reaction between fusion-mixture and mineral grains. If the latter are uraniferous then the reaction zones will contain the uranyl ion and will fluoresce with a bright yellow color in ultraviolet light of either short or long wavelength. Mineral particles that were shown by chemical analysis to contain approximately 0.10 per- cent of UO2 produced reaction zones that fluoresced brilliantly. It should be noted that this test may be used for detection of columbium in minerals devoid of uranium (Mackay, 1951 A, 1951B) but with much care and some reservation when uranium is also present.* Magnetite and Ilmenite. With few exceptions, for in- stance, the sands from near or at the mouths of Ario Nuevo Creek and Pajaro River, ilmenite is more abun- dant than magnetite, and in many cases this predomin- ance is a very striking one (e.g. Gazos and Whitehouse Creeks). In addition both minerals show marked gran- ular variation (van Andel, 1950, p. 9 J since, in most instances, magnetite and ilmenite with grain diameters ranging from 62-250 microns are more abundant than any other grain size. Both oxides usually form moder- ately abraded equidimensional particles with euhedral and subhedral fragments much less common. Only rarely has it been possible to identify any of the forms pre- served on subhedra or partially rounded grains of il- menite, whereas the octahedral form of magnetite is often evident. A slight iridescence or polychromatic film is somewhat more distinctly and more often developed on ilmenite than it is on magnetite, and this observation is not strictly comparable with that made earlier by the present writer (Hutton, 1950, p. 672) for placer mate- rial, beach and river sands. Magnetite is jet black in color and in common with members of the spinel group • In this connection, see particularly comment by Home in Mac- kay, 1951B, viz. pp. 250-252. exhibits a shining luster and distinct conchoidal frac- tures, the concavities and convexities of which tend to be small. These properties are in contrast to those ex- hibited by anhedral ilmenite which has a less decided luster to the black color. Magnetite only occasionally exhibits films of brown or reddish-brown iron hydrox- ides, and this might be expected in a situation where the grains are in a state of constant motion (compare magnetite in placer material or older river gravels, Hut- ton, 1950, p. 672). Quantitative analyses of ilmenite and magnetite have not been made but the following chemical data have been determined for a few examples. (1) Ferromagnetic magnetite which appears to be homogeneous often contains appreciable Ti 4+ ; this is presumed to be titanomag- netite. (2) Black octahedra, or fragments thereof, may show a distinct range of magnetic susceptibility, and if these crystals are isolated, crushed in oils, and viewed in transmitted light, the red trans- luceucy and anisotropic character thereof suggests that the mate- rial is martite or martitized magnetite. (.3) Some ilnienites have been observed to produce distinct fluorescent haloes in short wave ultraviolet light when tested with Howie's flux, and are apparently uranium-bearing. By comparison with the effects produced in minerals of known uranium-content, the ilnienites tested almost certainly contain less than 0.5 percent of UO». The presence of uranium in ilmenite raises the question of relationship with davidite (Mawson, 1916, 1944) and a com- parable mineral from Mozambique (Bannister and Horn, 1950), both of which contain much higher percentages of uranium, and are in a metamict state. When it is possible to concentrate a few milligrams for analysis and X-ray diffraction, this question will be considered further. Chromian Spinel. Members of the chromite series of light to deep brown color are generally present in all size fractions. In a number of instances they appear to make up the bulk of opaque and semi-opaque minerals, but opacity of larger fragments and particles hinders accurate determination of frequency. If, however, mag- netite and other ferro-magnetic material are removed first, the ilmenite-chromite fraction can be concentrated in a separate fraction when the Frantz separator is set at a slope of 10° and a tilt of 5°, and a current of 0.25-0.30 amps, is used ; the current will, of course, de- pend to some extent on the composition of the spinel. If the material attracted under these circumstances is viewed with a binocular microscope and oblique illumin- ation chromite, even if well rounded, may be readily distinguished from ilmenite on account of the character- istic jet black color, smooth conchoidal fractures, and brilliant shining luster. Nevertheless care must be ob- served in grain-counting since some compositions of martitized magnetite with similar susceptibilities to those of some chromites, may be present in the same magnetic fraction. On the basis of refractive index determinations alone, the composition of members of the chromite series ex- hibit a distinct, yet rather narrow range, and for most examples 1.970-1.985 was found to be general (e.g. ma- terial from sands at Bolsa Point). Chromian spinel from the mouth of Gazos Creek is, however, attracted by a much weaker field than is chromite from other samples studied, and a darker brown color is evident. Refractive indices are decidedly higher, and a range of 2.02-2.04 includes most of the members of the series in Gazos Creek material ; a few grains are in excess of 2.04 and a somewhat larger number range down to 1.975. 22 CALIFORNIA DIVISION OF MINES [Special Report 59 Pyrite. Pyrite may be recognized in a number of sands as buck-shot-sized spherules, cubes, dodecahedra, and subhedral to anhedral fragments. However, visual recognition is only positive when some indication of form is present or remains undestroyed in subhedral fragments. If grains are anhedral or abraded, their identification may be difficult or uncertain. Color changes resulting from oxidation may lead to mis- identification, or minerals such as chalcopyrite, marca- site, or arsenopyrite may be overlooked. However, none of these minerals were recognized with certainty, and even if they were misidentified, they would be fewer than 1 grain in 300. When a new screen is employed an appreciable quantity of brass in thin flakes is removed initially from the surfaces of the cloth and holders by abrasion ; it ac- cumulates chiefly in the pan along with the finest mineral fraction. At first glance this waste has the ap- pearance of thin fragments of pyrite but may be easily identified by the relatively smooth, wavy surfaces of the metal particles, their flexibility, and ready solubility in dilute HNO3. Galena. Galena, in sand from Bolsa Point,* consti- tutes approximately 82 percent of the — 250 fraction. This is, however, a very small percentage of the total unfractionated sample since particles with diameters less than 62 microns make up only 0.03 percent of the sand. The mineral occurs in a variety of shapes whose form has been determined principally by perfect cubic cleavage. In oblique illumination a bright grey color is evident for most fragments with a thin white film or surface, possibly cerussite, noticeable here and there. It is not attracted by strong magnetic fields, and ac- cordingly is found in the rejected fraction along with zircon, apatite, rutile, brookite, etc. Euxenite-Poly erase Series. In blacksand paystreaks at the mouth of Aiio Nuevo Creek very rare fragments of a member of the euxenite-polycrase series were de- tected in the form of nearly opaque, deep brown grains of marked luster and striking conchoidal fracture. Thin splinters are brown in color, quite isotropic and, there- fore, metamict. Refractive index is slightly in excess of 2.05. Following heating at 650° C. in air for one hour, a distinct rise in refractive index was evident and, al- though good X-ray diffraction powder patterns were then obtained with single fragments, anisotropy was not evident optically. Positive tests for tantalum and nio- bium resulted from the tannin method (Schoeller, 1937, p. 89), since, following prior removal of titanium by tartaric hydrolysis, a tannin complex of orange-red color was formed. The positions and intensities of the lines in the X-ray powder pattern of the heated material, correspond al- most exactly with those determined by Arnott (1950, ]>. 396) for undoubted euxenite from Nipissing, Canada, although there are some additional lines in the Ano Nuevo Creek material. However, these slight divergences could be due to an inadequate ignition temperature, and ii addition, might be expected in view of the variability of cell dimensions of euxenites as reported by Arnott. In this instance, heating to somewhat lower tempera- * In this instance, the relative abundance of galena suggests that its presence may be ilventitious Accordingly, in view of this prob- ability, it was not 1 ed in table 1. tnres did not yield a product that gave pyrochlore or uraninite-type patterns. The powder pattern of Aiio Nuevo euxenite is com- pared with that of euxenite from Mattawan Township, Nipissing District, Ontario, in table 8. Table S. Poivder patterns of euxenite. Camera diameter : 114.59 mm. Radiation : Ni-filtered copper (\ = 1.5418 A). A B I d meas. I d meas. hkl /4d \5d 11.6 9.9 .. .. __ 1 7.30 (020) P 6.13 _. ._ 5.85 __ 2 5.16 (110) 4 3.62 3 3.66 (130), (111), (040) 1 3.32 2 3.36 (121) 10 2.96 10 2.98 (131) 3 2.93 .. 4 2.76 2 2.77 (200) 5 2.61 H 2.61 (141) 4 2.57 2 2.58 (002), (220), (150) __ a 2.54 (012) 4B /2.42 1.2.40 3 2.43 (022), (201), (060) 3— 2.30 1 2.30 (112), (221), (151) M 2.252 (032), (122) 3 2.193 l 2.199 (240) 2 2.178 l 2.182 (231) 4 2.106 2 2.106 (132) H 2.071 (161) J 9 y* 2.025 (241) 1 1.961 M 1.970 (142) 1 1.926 i 1.935 (170), (052) 5 1.886 2 1.889 (202) 6 1.817 4 1.823 (222), (310), (152) (260), (171), (080) 5 1.792 _. __ 6 1.759 3 1.769 (062) 6 1.720 4 1.723 (311), (330), (261) __ __ V2 1.679 (242) 4 1.622 3 1.635 (181), (113), (331) followed by many additional lines, none of which exceed a scale of 4 in Arnott's scheme. A. Euxenite from the mouth of Alio Nuevo Creek, San Mateo Co,, California. I am indebted to Professor Adolf Pabst of the Uni- versity of California for his kindness in providing these X-ray diffraction data for me. B. Euxenite, Mattawan twp., Nipissing District, Ontario, Canada (Arnott, 1950, pp. 396-7, table 5). d = diffuse line. B = broad line. Pumpellyite In addition to occurrence in composite fragments, individual rounded particles of aggregates of fine pris- matic crystals of pumpellyite are found, and for indi- vidual crystals therein, the following data were deter- mined in one instance (Aiio Nuevo Creek) : Elongation 2V Dispersion 1.685-1.690 Y. 70° ( + ) strong with r >5 amps. (8) Same as no. 7. (9) Same as no. 7. (10) Hypersthene with clear remnants at crystal extremities that have the appearance of outgrowths. Fraction, locality, and mag- nification as for do 7. (11) Pale green augite. — 25 fraction of beachsand from a point north of the mouth of San Gregorio Creek, San Mateo County. N K). (12) Same as no. 11. (13) Hypersthene. — 115 +250 fraction of Aptos beachsand (magnetic fraction — 0.10 + 0.35 amps). X 125. 5ame as no. 11. (15) Hypersthene. Fraction, locality, and magnification as for no. 11. (16) Same as no. 11. (17) Same is no. 15. (18) (ilomeroporphyritic aggregate of hypersthene crystals. — 32 +60 fraction of Aptos beachsand. X 54. (19) Same as no. 11. 20) Titan-augite, much chipped. Fraction, locality, and magnification as for no. 2. (21) Green augite oriented parallel to (010). Fraction, icality, and magnification as for no. 13. (22) Clear, slender hypersthene crystal in heavy residue from I'urisima formation. North of mouth of San Gregorio Creek, San Mateo County. X lcSO. (23) Same as no. 21. 1959] MINERALOGY OF BEACH SANDS 25 110s. 10, 22) ; the cuhedral ones are perhaps more usual in finer size fractions but are also found among' the coarser sizes. Occasional undamaged glomeroporphyritic aggregates have been found (fig. 4, no. 18) in which the individuals show no simple crystallographic relation- ship to one another ; twinning is thus discounted. As with augite, hypersthene exhibits every degree of completeness of solution effects from incipient develop- ment of multiple pyramidal terminations (fig. 4, nos. 6-9) to minute fragments with very slender, needle-like attenuations that are often two or three times as long as the central remnants (fig. 4, nos. 15, 17). It should be noted at this point that fragments with the most pro- nounced solution effects, that is, remnants with the long- est and most delicate pyramidal terminations, are more or less restricted in their distribution to the finest grade size ; in other words, to grains with diameters not in excess of 62 microns. Larger pyroxene fragments (125- 250 microns) exhibiting solution effects show some de- gree of blunting of the multipyramidal terminations, and extremely attentuated needle-like fringes are ap- parently unable to develop or to be maintained in such instances (fig. 4, nos. 8-9). This would appear to be a fine example of the incompetence of abrasion processes, even on open beaches exposed to storm conditions of some violence, when minute particles are cushioned by water films. In the samples investigated the minute fragments with attenuated fringes did not appear to be limited to any particular zone of a beach and do not seem to be any more numerous at storm level than at low water mark. The finest sized particles of hypersthene are colorless or nearly so, but coarser material is moderately pleo- chroic according to the usual scheme. Distinct dif- ferences in absorption between the three vibration directions are difficult to detect but where absorption is most pronounced the scheme X > Z J> Y would seem to apply. In some preparations hypersthene fragments were found to be oriented in the mounting medium with the basal plane parallel to the plane of the microscope stage, and at first sight the pleochroism, brown (X) to golden yellow (Y), suggested that of staurolite. However, such grains were perpendicular to the bisectrix Z and have other properties characteristic of hypersthene. Except for specimens from occurrences near Pajaro River, refractive indices fell within the following range in the majority of samples : a = 1.685 — 1.688 y = 1.698 — 1.700 7 — = 0.012 — 0.013 Zoning may be quite marked and is made more apparent by distinctly stronger absorption in narrow peripheral zones that are not necessarily abruptly demarcated from the central areas. In material collected just above high water level, three-quarters of a mile south of the mouth of Pajaro River, the following values were obtained : a= — , 1.694, 1.696, 1.696 Y = 1.699, 1.708, 1.710, 1.710 Taken together, the refractive indices indicate a com- positional range of 33-42 percent of the orthoferrosilite molecule (Henry, 1935, p. 223, fig. 1). Very few hypersthene fragments are completely de- void of inclusions, and the following are common : (1) Rounded or irregula rly shaped grains of magnetite, titano- magnetite and ilmenite ; on account of the abundance of these contaminants in some cases, pyroxene crystals may lie ferro- magnetic or so strongly paramagnetic that they are concentrated with ilmcnite when the sands are magnetically fractionated. (2) Unidentified disoriented, colorless grains of low refractive index. (3) Irregularly shaped and spaced gas cavities; occasionally these may be grouped into dense aggregates. (4) Prismatic crystals of apatite. (."-)) Glass. Mi) Euhedral zircon. (7) Most, or combinations, of the minerals or phases just listed may be found aggregated into distinct zones that exhibit marked parallelism to orthopyroxene crystal boundaries. Rutile Rutile, a constant minor constituent, does not exceed 1 percent of any fraction of any of the sands studied. Worn and broken prismatic crystals with rare geniculate twins are characteristic and these exhibit either (a) golden yellow to red-brown dichroism with intense ab- sorption parallel to the c axis in a few cases, or (b) golden yellow to yellowish-brown for the ordinary and extraordinary rays respectively, with little difference in absorption in the two directions. In the — 60 -f- 115 size fraction, Whitehouse Creek material contains fragments that are very deep red in color and almost opaque for any orientation. A score of fragments were hand-picked and after fusion in potassium pyrosulfate and solution positive tests for tantalum were obtained; the presence of niobium was not verified. In oblique illumination rutile may be readily identi- fied and differentiated from oxyhornblende, cassiterite and other dark brown prismatic minerals by its adaman- tine luster; the presence of striations is an assistance. When color is intense rutile fragments are nearly black in oblique lighting but are, however, rarely devoid of a dark brown resinous glint ; the latter is particularly evident where conchoidal fractures have partially devel- oped without actual separation of splinters. Sphene Sphene is ubiquitous and, in general, crystals and fragments that have diameters ranging from 125-250 microns are noticeably the more abundant. Habit varies considerably from grain to grain but the range of forms does not change appreciably from sample to sample. Every gradation is to be found from sharply euhedral "envelope "-shaped crystals with dome {102}, basal plane {001}, and orthopinacoid {100} prominently de- veloped, to fragments of euhedra, or on the other hand, well rounded particles that may exhibit chatter marks. In crystals from the south side of the mouth of Tunitas Creek, deep rhomboidally shaped pits were seen, and at the same time pronounced zoning was made evident solely by patchy distribution of anomalous interference tints in orientations with Bxa perpendicular, or nearly so, to the microscope stage. Two varities of sphene have been noted and both of these are usually present in the same sample. The first of these forms pale yellow, well worn grains with a dusty appearance that may be due to numerous unidenti- fied translucent, pale yellow to colorless inclusions. Nu- merous cracks are present that do not seem to originate 26 CALIFORNIA DIVISION OF MINES [Special Report 59 at any specific point or inclusion. Due to the degree of rounding, preferred orientation of crystals in mounting media is not very noticeable. Dispersion is distinct and pleoehroism faint yet clear, with X' = pale yellow to nearly colorless and Z' = deep salmon pink (rarely red- brown ; Whitehouse Creek), in some instances, but with X' = pale golden yellow and Z' = golden yellow domi- nant. Pleoehroism may be much more satisfactorily ob- served when crystals, or fragments thereof, are immersed in a liquid of refractive index about 1.95, since, in mounting media of very dissimilar refractive index, ap- propriately oriented crystals exhibit marked change of brightness on rotation of the microscope stage due to high birefringence ; this effect of alternate brightening (X' parallel to plane of polarized light) and darkening (Z' parallel to plane of polarized light) is suggestive of pleoehroism. The second variety of sphene is also pale yellow, although in some instances nearly colorless, and crystals and fragments are generally free from inclusions. Round- ing is less noticeable and angular, or often euhedral forms with {102} prominent, are more common. Pre- ferred orientation of grains in mounting media is much more obvious than is the case with the first variety, interference figures are clearer, dispersive effects are more striking both in interference figures and between crossed nicols, and the optic axial angle is greater. Cracks are not so evident. No significant differences in the a refractive indices have been detected so far, and values that range from 1.887 to 1.898 have been found for the two varieties. Ad- ditional work in this connection is necessary. Tantalite Identification of rare, dark red, irregular fragments in material from the mouth of A no Nuevo Creek as tantalite is somewhat doubtful, but the data determined are recorded for the sake of completeness and to point out that distinction between tantalite and deeply colored tantalian cassiterite, on the basis of some optical prop- erties alone, may not be entirely satisfactory unless com- plete information can be obtained. The refractive index for X' is in excess of 2.06 (distinction from cassiterite) but birefringence does not appear noticeably different from that for cassiterite. Fragments are unaffected by hot concentrated HC1, give a negative test for Sn 4+ with zinc and HC1, and curiously, if tantalite is a correct diagnosis, contain negligible Mn 2+ ; with tannin, orange colored complexes of Ta 5+ and/or Nb r,+ compounds were obtained. Cleavage is not apparent, nor could satisfac- tory interference figures be secured. Uranoan Thorite Uranium -bearing thorite, a constituent of many sands collected at points between Princeton and Monterey Bay, is largely restricted in size to diameters less than 125 microns. Habit and Color. Most thorite forms exceptionally well abraded particles, occasionally spherical, with traces of conchoidally shaped fracture surfaces that are very nearly obliterated by the natural polishing processes to which the mineral has been subjected. There is every gradation between such forms and less common stumpy, prism-like, grains from which all traces of crystal faces have been removed, and, in the other extreme, highly angular fragments with strikingly well developed con- choidal fractures. No grains were found with definitely identifiable crystal faces. A rather wide range of color is found and an opal- escent pale green, close to Ridgway's Light Grape Green (25'" YG-Y, b) is possibly the dominant one. A shade of brown is less often evident whereas some crystal frag- ments trend towards Ridgwav's Corydalis Green (29'" GG-Y, d). A color- close to Courge Green (25 YC-Y, i) is found for a few grains with Orange-Citrine (19 YO- Y, k) unusual. Almost colorless particles are rare. The color of a pure sample of uranoan thorite particles with diameters 62-125 microns is comparable to Ridgway 's Yew Green (27" G-Y, m) when viewed en masse in ordi- nary light. The prime cause of the wide range of colors found in Aiio Nuevo Creek thorite is obscure. The green opalescent color that is most commonly seen may result from the presence of U 4+ ions, and perhaps much paler yellowish green tints might arise when U 0+ ions are dominant instead. On the other hand, the range of colors displayed by this mineral is rather strikingly similar to that found in common silicate glasses with comparable or less amounts of iron to that found in this mineral (table 9), that have been prepared under a variety of oxidizing and/or reducing conditions. The range of color that may be developed in such cases is clearly due to the small percentage of iron present, but little appears to be known of the relationship between the valence of iron and the color of the corresponding glass. Certainly, it is not merely a question of divalent iron producing a green glass, and a brown glass resulting from oxidation of iron to the trivalent state, since in some instances, green "lasses have resulted with iron in the higher state of oxidation ; even blue colors have developed in glasses when approximately equal amounts of Fe 2+ and Fe 3+ are present. That thorite, described here, is in a glassy, metamict condition, does not make the comparison with artificial silicate "lasses any more valid, since a wide range of color from green to brown may be observed in non-metamict thorite. Thus little specific data are available to assist in re- solving this question of color, but it is tentatively sug- gested that the range of color in thorite may be due to the iron present, rather than to the uranium content. The range of magnetic susceptibility found for this mineral may support this conclusion. In oblique illumination uranoan thorite is readily dif- ferentiated from other pale green or brownish green grains, such as many composite fragments of saussuritic composition, grossular, members of the clinozoisite- epidote series, vesuvianite, etc., first, by striking opal- escent or chatoyant appearance, and second, by remark- ably smooth and polished surfaces of the rounded particles. Here and there, for example at the mouth of Gazos Creek, thorite may exhibit curious breadcrust- like surfaces that are particularly evident in brown- colored varieties but not restricted thereto. In shortwave ultraviolet light (2540 A.) a very faint deep blue fluorescence was detected for some particles, but when these were segregated by hand-picking and examined in liquid media by transmitted light, nothing distinctive was detected. On the other hand, a blue 1959] MINERALOGY OF BEACH SANDS 27 fluorescence of brighter hue was noticed for patches of alteration ( ?) material associated with some thorite, and, here and there, bright yellow-green fluorescent spots suggest the presence of uranyl compounds as other alteration products. No effects were noted when ultra- violet light of longer wavelength (about 3600 A) was employed as the source of oblique illumination. The ability of uranoan thorite described herein to produce faint fluorescence in shortwave ultraviolet light appears to be' destroyed by heating to temperatures in excess of 680°C. Inclusions. Inclusions are uncommon, and especially so for highly translucent clear green varieties ; on the other hand, alteration products appear to be slightly more frequent in brownish grains than in green. Some of the inclusions and heterogeneities observed may be summed up as follows : (1) Brown areas that appear due to clouds of "limonitie" dust- like particles in grains that otherwise exhibit blotchy areas of weal; birefringence. (2) Zonary arrangement in which relatively wide brown central areas of dusty aspect are sharply demarcated from clear, green peripheral zones. (3) Yellow to orange colored blotches, often anisotropic, in otherwise homogeneous, inclusion-free crystals of pale green color. The yellow or orange material is soluble in warm dilute HNOa, and since this solution fluoresces in shortwave ultraviolet light, the presence of the uranyl radical in these distinctively colored areas is suspected. (4) Aggregates of unidentified dust-like particles from which systems of cracks may radiate outward. (5) Semi-opaque isotropic areas of much lower refractive index than the thorite. (6) Sharply demarcated, unsymmetrieal narrow zones of color banding, (fig. 5, no. 9.) (7) Cavities filled with gas or liquid; rarely bubbles (fig 5, no. 19). (8) Systems of anastomosing cracks, usually thread-like, that do not seem to be associated with inclusions of any kind. (0) Deep brown opaque inclusions; usually as rounded grains or blebs. When free from inclusions or from what seem to be alteration products, uranoan thorite is generally iso- tropic, though a few grains have a faint glimmer of bire- fringence. A spherulitic structure on a eryptocrystalline scale is suggested for the birefringent grains on account of the appearance of minute black crosses when such material is viewed between crossed nicols; the arms of the crosses are parallel to the ocular cross hairs and the direction parallel to the elongation of the "fibers" is fast. Chemical Properties. Uranoan thorite is exceedingly refractory and even when reduced to excessively fine powder, hot concentrated acids have little effect thereon, and gelatinization was not evident. However, if frag- ments of thorite are boiled in a strong solution of oxalic acid for about 2 minutes, washed, and then dried, white films of thorium oxalate are developed; this behavior facilitates recognition of thorite when other green, iso- tropic, but non-thorium-bearing minerals are present. A sample was prepared by careful electromagnetic frac- tionation, after preliminary concentration by screening and flotation, and brought to a state of high purity by careful hand-picking in oblique illumination Avith white light and finally with shortwave ultraviolet light. The latter precaution was necessary in order to guarantee absence of both zircon and scheelite; neither ZrO^. nor W0 3 were detected by analysis. The composition of thorite from A no Nucvo Creek is quite similar to that recorded by George (1951, p. 131) for thorite from concentrates obtained by the La Grange Dredging Company in the course of opera- tions on the Tuolumne River, near La Grange, Cali- fornia. However, uranoan thorite from the Aho Nuevo locality contains an appreciable amount of copper and the total quantity of water is released at tempera- tures below 105° C. The. analysis of Tuolumne River thorite, on the other hand, shows moderate amounts of alumina and water, although George does not give any indication of the temperature at which water was given off; in fact, the considerable quantity of water in thorite from the Tuolumne River locality is not com- mented upon by George, other than to state that the high specific gravity "is probably attributable to the absence of appreciable water of hydration." Table 9. Analyses of uranoan thorite. A. B. Rare earths 0.24 0.54 Th0 2 72.93 71.61 U0 2 6.95 8.36 FeO 0.58 0.59 A1 2 3 0.32 1.29 TiOo 0.04 0.10 MnO <0.01 CuO _' 0.11 PbO 0.1O 0.10 CaO — 0.42 MgO 0.07 0.01 PjO= trace Sif) 2 17.96 16.47 H,0 + nil , rteP H,0— 0.22 p HO 99.94 100.00 A. Uranoan thorite separated from blacksands, mouth of Aiio Nuevo Creek, San Mateo County, California. TasOn, NbsOo, Zr0 2 , and WO.i were not detected. Rare earths are chiefly Y 2 Os. Analyst : Johnson, Matthey. B. Uranoan thorite from dredge concentrates, La Grange, Califor- nia. Total includes Zv0 2 0.07 per cent (George, 1951, p. 131, column 3.). Analyst: National Bureau of Standards When the two thorite analyses are calculated on the basis of molecular proportions the ratio of ThO a and other metal oxides to silica is low in each case, when it should be 1:1. For the Ano Nuevo mineral Th0 2 etc.: SiC\> is 1:0.903, whereas the corresponding ratio for thorite from Tuolumne River (George, 1951, p. 131) is 1:0.845, a discrepancy which George believed might be due to an incorrect silica determination. Although this could be the ease, it should be remembered that we are unaware of the states of oxidation of both iron and uranium. Certainly in view of the low percentages of Fe- + an incorrect assumption in this respect will be of little moment but with uranium it is a different matter. Frondel (1953) has demonstrated that [Si0 4 ] groups in thorite may be replaced by [OII] 4 in a manner sim- ilar to that found in hydrogrossular and other minerals. If, then, the two analyses in table 9 are recalculated on the basis of 16 oxygen atoms to the unit cell, and water is taken into consideration (table 10), much better ratios between Th etc. and (Si+H) are obtained (1:0.98 and 1.08 for A no Nuevo Creek and Tuolumne River thorite respectively). This seems to support the conclusion that the water determined to be present in these two minerals may instead, be [Oil] 4 substituting for [Si0 4 ], rather than water molecules, although it should be stressed that the 0.22 per cent of ILO in Aho Nuevo Creek 28 CALIFORNIA DIVISION OF MINES [Special Report 59 FIGURE 5. Typical habit and form of detrital uranoan thorite. Locality, beachsands at the mouth of Alio Nuevo Creek. Magnification, X '100. (1) Slightly abraded, green thorite of tetragonal form. (2) and (3) Abraded and chipped, green anhedra. (4) Excessively chipped and rounded grain; color pale green. (5) and (6) Chipped, abraded grains; pale green. (7) Poorly birefringent, orange-colored thorite. (8) Isotropic orange thorite. (9) Abraded brown thorite with bands of inclusions of dust-like size, but undiagnosed. (10) Abraded chip of dirty green thorite. (11) Well-rounded clear green thorite. (12) Pale green thorite with semi-opaque inclusions; striations may be zonary structure. (13) Deep green abraded grain with lines of submicroscopic inclusions. (14) Green fragments, per- haps a basal section. (15) Deep green particle of thorite. (16) Practically colorless thorite with chatter marks. (17) and (18) Clear brown grains. (19) Clear green particle with gas cavities. 19591 MINERALOGY OF BEACH SANDS 29 Table lo. Recalculation of thorite analyses on the basis of Id oxygen atoms per unit-cell. Table 11. Effect of heating on physical properties of Ai'io Xitcro thorite. A. B. Ano Nuevo Creek Tuolumne River, (La Grange) Weight percent Metal atoms Weight percent Metal atoms R.E.* TI1O2 UO2 FeO AI2O3 Ti0 2 CuO CaO MgO S1O2 H2O 0.24 72.93 6.95 0.58 0.32 0.04 0.11 0.42 0.07 17.96 0.22 .03' 3.54 .33 .10 .08 .01 .09 .02, 3.84/ .31/ 4.20 4.15 R.E.* TI1O2 UO2 FeO AI2O3 TiOa CuO CaO MgO Si0 2 rhO 0.54 71.61 8.30 0.59 1.29 0.10 0.01 16.47 0.86 .06 3.45 .39 .10 .32 .01 3.49\ 1 .2l/ 4.33 4.70 Formulae : A. [Th3..i4 U0.33 Yo. 03 Feo.10 Alo.os Cuo.m Caoiw Mgo.02] [SiC>4]3.s4[ (OH)4]o.3i B. [Th3.45U0.39 Y0.00 Feo.io Alo.su Tio.01] [SiCk]s.«>[ (OH)<]i.a * R.E. refers to rare earth.s and in both instances these have been taken to be yttrium. thorite was given off below 105° C. The ratio of 1:1.08 in Tnolnnme River thorite is, of course, too high, and some water molecules may be present as well in this case. Although the work of Frondel has shown that altera- tion of primary thorite to hydrothorite gives rise to a product that is fully crystalline, and not metamict, the minerals described here are metamict. Physical Properties. The mineral is either isotropic, or at the most, it may exhibit feeble birefringence ; ac- cordingly, it is in a metamict condition. In no instance, however, were values comparable to those recorded by George (1951) for La Grange, Tuolumne River thorite observed, nor has the present writer ever found bire- fringences of the order noted by George in his own con- centrates of Tuolumne River thorite. A range of re- fractive indices has- been determined for the analyzed material, and 1.850±0.002 appears to be inclusive. For impure thorite concentrates, a range of 1.841-1.859 was found, but with the greater proportion of the material lying within the range 1.849-1.854. Both refractive in- dices and color undergo marked transformations when Ano Nuevo thorite is heated in air, and the data in table 11 are indicative of these changes. Since heavy media could not be profitably employed for specific gravity determinations, a micropyenometric method was used ; this entailed use of several milligram amounts of thorite grains, rather than individual par- ticles, and the values obtained in this manner for sev- eral pure fractions that exhibited slightly differing magnetic susceptibility were 6.27±0.03 at 26° C. Employing a camera of 57.3 mm. diameter, and nickel- filtered copper-radiation, a faint, but well-defined pow- der pattern was obtained from a single crystal of uranoan thorite, 0.125 mm. in length, after it had been heated in air for 4 hours * at a temperature of 860° C. The lines on this pattern are those yielded by the face-cen- tered cubic lattice of thorianite (table 12). After de- mounting' the crystal, it was heated again, but this time to a temperature of 1250° C. for an additional four- hour * period, and the X-ray diffraction pattern now * It was determined in subsequent experiments that much shorter periods of heat-treatment would cause satisfactory recrystalliza- tion of metamict thorite. Refractive indices Temperature in degrees Centigrade Major portion Range Color in transmitted light Normal 680° for 2V 2 hours 800° for 3J4 hours- 860° for 4 hours. .. 1.850 1.865 1 . 838 1.805 1.788 1.841-1.859 1.858-1.869 1.829-1.842 1.799-1.808 1.779-1.791 Pale green Golden brown Golden brown 1100° for 4 hours Very dark brown, (dark coffee brown in oblique illumination). Table 12. Poieder pattern of uranoan thorite after being heated to 860° C. for four hours. Locality: Mouth of Ano Nuevo Creek, San Mateo County, California. dot, hkl I* 3.23 (111) 10 2.78 (200) 6 1.96 (220) 7 1.69 (311) 8 1.62 (222) 2 1.40 (400) 2 1.29 (331) 4 1.26 (420) 3 1.15 (422) 3 108 ((511)1 1.08 J (333) I 0.09 (440) v. faint 0.95 (531) 2 04 f (600) ] „ U.J4 ^ (442) ^ 2 0.S85 (620) 1 * Intensities were determined visually. obtained from the crystal corresponds to that of the monoclinic dimorph of Th,Si0 4 — huttonite. Age of Ano Nuevo Creek Thorite. While fully cog- nizant of the uncertainties attached to age determina- tions of material that has not been found in place, it is interesting that the ratio U-Th/Pb for Ano Nuevo Creek thorite leads to an age of 25.25 x 10° years when Holmes' (1931, p. 207) logarithmic formula is employed, and that this is close to the age of 21 x 10° found by George (1951, p. 130) for Tuolumne River thorite of placer origin that was apparently derived from Sierra Nevada intrusives. Although the original host of the Ano Nuevo Creek thorite is not known, it would seem most probable that it has been derived from Sierra Nevada intrusives. Ac- cordingly, an age of 25.25 x 10 r ' years is quite unlikely, and in view of the well-known solubility of the thorium- lead isotope, Pb 208 , a loss of lead may have taken place during the process of metamictization, or perhaps dur- ing the transfer to its present locality — especially if acidic ground-waters were available. Topaz Topaz was recognized in the finest size fractions of two samples as water-clear, but irregularly shaped cleavage fragments that exhibit centered biaxial interference figures. Tourmaline Tourmaline, surprisingly rare hut widely distributed, usually forms abraded or fragmentary short to stumpy prismatic crystals with terminal faces that are occasion- ally preserved. Clouds of dust-like particles are often 30 CALIFORNIA DIVISION OP MINES [Special Report 59 present and parti-colored fragments were rarely seen. Crystal fragments with quite intense dichroism in shades of brown appear to be dominant, with blue or purplish tints much less abundant, Other dichroic schemes infrequently observed are == red, E = color- less (Aiio Nuevo) ; O = deep green and nearly opaque, E = pale green (Bolsa Point); = deep greenish brown, E = red-brown (Butano Creek). Vesuvianite Rare vesuvianite forms rounded to sub-rounded color- less to very pale green grains of faint birefringence, but material from sands at the mouth of Whitehouse Creek was rather distinctive ; the following data were deter- mined for it : 1. The mineral was concentrated electromagnetically when the separator was set with a slope of 15°, a tilt of 5°, and a current of 0.45 amps, was employed. 2. a = 1.710 ± 0.002 T = 1.719 7 — a = 0.003 o. The optic axial angle was zero in red light, but a small angle is evident in light near the short end of the visible spectrum ; sign is positive. These data are comparable to those given by Winchell (1951, p. 508) for the variety, viluite, but since insuffi- cient material is available for any additional work fur- ther comparison is unwarranted at this time. Xenotime The yttrium phosphate xenotime has been definitely recognized in one heavy mineral assemblage, the — 115 -f250 mesh fraction of material from the mouth of Aho Nuevo Creek. It was found concentrated in the electromagnetically separated monazite-rich fraction, al- though xenotime was found to have a greater suscepti- bility than that of monazite. Xenotime forms colorless, rounded, equidimensional grains of dusty aspect due to fine pale colored inclus- ions which are often aggregated together to produce what at first sight has the appearance of a stain. It is uniaxial and optically positive with a = 1.724 and y = 1.818. Tests with alpha-track plates suggest that the xenotime described herein is distinctly more radioactive than the associated monazite but otherwise no compositional data are available. Zircon Zircon is a constituent of each of the size fractions —250, —115 +250, and —60 + 115 in every sample studied. In the first size group zircon may range from 75 percent down to approximately 1 percent, but with higher values the more usual ones. Zircon exhibits very much the same range of frequency in the second size fraction, but in the — 60 -j- 115 and coarser grade sizes zircon percentages decrease rapidly. It is found in a wide variety of forms and, except for the more obvious division into colorless and purplish types, no simple classification appears to be possible. Colorless Zircon. By far the greater proportion of zircon in the finest size fractions is euhedral but the de- gree of rounding increases strikingly with increase of /rain-size and may attain considerable perfection with the development in some instances of cigar-shaped forms. Crystals less than 62 microns in diameter show little evidence of abrasion whereas the larger crystals or fragments in the — 115 -f 250 fraction do. Fragments bounded by conchoidal fractures are found in the finest fractions but they are increasingly less frequent in as- semblages of larger grain size. In more rounded grains pits and chatter-marks are often seen by inspection in oblique illumination. The dimensions, that is length and breadth, of euhedra show a fairly wide range but no distinct groupings seem feasible. The ratio length: breadth ranges from 1.9-4.5 with the majority of grains from all samples, 2.2-2.5. Crystals of moderately complex habit are dominant whereas crystals with first order prisms and pyramids alone are decidedly rare. Perhaps the most common forms developed in any one crystal are m {110}, a {100}, x {311}, p {111}, and u {331}. Inclusions are general, and although few grains are de- void of them, only rarely is a considerable amount of the zircon of any one sample moderately paramagnetic on account of aggregates of opaque iron oxides ( — 115 -4- 250 fraction of material from near the mouth of White- house Creek). The common forms of inclusions observed are : (a) T'noriented needles of dark brown material (=rutile V). (b) Narrow thread-like channels parallel to the c-axis that may be gas-filled since the refractive index is extremely low. (c) Prismatic laths of ilmenite and more or less rounded grains of magnetite. (d) (Jaseous and liquid cavities. (e) Colorless, acicular crystals as yet unidentified. (f) Prisms of rutile, apatite, zircon, monazite. Occasional zircons of faint blush pink color were noticed and such crystals are probably more correctly in- eluded with the group just described than with hyacinth, since they do not exhibit any of the characteristic features seen in hyacinth. Such zircons are generally sharply euhedral and perhaps more often free from in- clusions than colorless zircon ; otherwise they are similar. Hyacinth. The purple-colored variety of zircon, hya- cinth, is present in most assemblages but it rarely ex- ceeds more than a few grains in any one sample. Although restricted numbers did not permit detailed studies, the characteristic features of color, zonary struc- ture, notable rounding, anastomosing systems of fissures or cracks are all present, and comparable in every Avay to those previouslv recorded for hyacinth (Tyler et al., 1940; Ilutton, 1950). Malacon. In material from near the mouth of Tunitas Creek, San Mateo County, rare particles were observed that are believed to be malacon, but this opinion is put forward with some uncertainty. The dusty, brown, grains have tetragonal symmetry, and a birefringence that does not exceed 0.015. Refractive index and specific gravity are approximately 1.78 and 4.1 respectively. Doubtful Identifications In the foregoing mineralogical descriptions attention has been drawn to the uncertainty of some data and the interpretations based thereon. Furthermore in some in- stances optical data determined for some minerals may not correspond with any recorded data, or correspond in a general way only with some extremely rare or unusual species so that reference to such mineral types does not seem to be warranted. In every case where there was some doubt insufficient material prevented application of adequate chemical or optical tests. However, the incom- plete data are recorded in the hope that they may prove of use to other investigators. 1059] MINERALOGY OF BEACH SANDS 31 In a fraction rejected by the electromagnet at maxi- mum field strength occasional grains were recognized in material from the mouth of Alio Nuevo Creek ( — 115 -\- 250 mesh), with the following properties: Color : deep blue to bluish green. Pleochroism : faint. N : 2.0 (Cfl). Birefringence: 0.03 (ca). Uniaxial and optically negative. These data are comparable to those recorded for the hydrous oxychlorides boleite and pseudoboleite. From sands near the mouth of Whitehouse Creek oc- casional fragments were found in a magnetic fraction rejected at 0.75 amps but attracted at 1.18 amps, (slope 15°, tilt 5°), that have not been satisfactorily identified. Significant properties recorded for this mineral are : Colorless; one good cleavage; a = 1.685 ± 0.002; Y = 1.695; y — a = 0.010; 2V = 35 — 40° ( + ). These data suggest zoisite but dispersion is absent and that mineral has somewhat higher refractive indices; furthermore zoisite is attracted by much weaker field strengths than used here. In the — 60-(-115 fraction of material from the mouth of Gazos Creek rare fragments were noted with the following properties : Colorless, rounded fragments; a = 1.731 ± 0.002; Y = 1.752; Y — a = 0.021; 2V = 65° (— ) ; r > v, very strong. No chemical data are available. PROVENANCE Although detailed studies have not reached a state of completeness that would permit an adequate report con- cerning provenance, it may be stated that all of the minerals recognized in the beachsands with the excep- tion of cassiterite, chrysoberyl, corundum, diamond, dufrenite, euxenite, scheelite, tantalite, thorite, ve- suvianite, and xenotime have been found in assemblages of heavy mineral fractions prepared from Cretaceous and Tertiary sandstones, siltstones, volcanic ash beds, etc., in this area. Undoubtedly these must have pro- vided much of the detritus that is now differentially sorted and concentrated on the present day beaches. Study of heavy fractions prepared from soft brown sandstones of the Merced formation : (Lawson, 1914) proved instructive and pointed to a source for at least some of the deeply etched pyroxenes previously de- scribed, since both orthorhombic and monoclinic forms are very well represented in — 60 + 115 an d — H5 size fractions of the large residues. 2 The mineral frequencies, based on averaged counts of 300 grains in each of three samples of Merced sand- stones, are set out in table 13. The dominance of green hornblende is noteworthy, particularly since this is characteristic of beach sands concentrated at the north end of Half moon Bay (see Princeton samples, table 1, earlier in the text). In almost all respects the constituents in these as- semblages (table 13) are comparable to those described earlier, but the following differences in mineralogy and association should be noted : 1 These were collected at the north end of Moss Beach, approxi- mately 2\ miles north of Princeton. The sandstones immediately overlie course dioritic and granodioritic conglomerates which in turn rest upon Montara intrusive rocks. -'These averaged 2.6 percent of the total samples employed. Table 1.1. Mineral frequencies in henry residues from hroirii sandstones ill Hir 1/ creed foriiiiifion, —(in + 11.% — un Apatite 1 1 Augite i» Biotite 1 Clinozoisite-epidote 4 4 Composites (5+ "i (Jarnet 1 tllaucophane 1 1 Hornblende, green 7 — <>-f- Hornblende, brown 5 4 Hornblende, oxy-type 4 2 Hypersthene 4 6+ Kyanite 1 Opaque minerals (incl. chromite) 1 5 Rutile 1 Sphene 2 4 Staurolite 1 Zircon 1 1 Zoisite 1 Doubtful identification _ 1 (1) Habit of fbe constituents of the assemblages, irrespective of grain-size, is dominantly angular and accordingly this leads one to surest that vectorial solution of pyroxene and aniphibole frag- ments is actually taking place in these sediments, and is a normal process of the weathering of such material. (2) Brown and green hornblendes are often mere relicts within wide peripheral zones of later formed colorless tremolite. This is most suggestive of a transformation of hornblendes of igneous and other origin into non-aluminous amphiboles, or at least amphi- boles with a minimum of four-coordinated aluminum, that are stable at the low temperatures and pressures of sediments. (3) Semi-nephrites were found among the composite fragments. (4) Rare deep red-brown biotite has a wide optic axial angle (2V = 48°±2°) and such pronounced dispersion that basal plates do not go into extinction between crossed nicols, but instead merely change from red to greenish-blue on rotation of the microscope stage. (.">) Staurolite and kyanite, both representative of a high grade of metamorphism are present. Montara quartz diorite crops out over a wide portion of the distributive province at the northern end of the area treated here and heavy fractions prepared from 22 samples, though exceedingly small in volume, con- tained the following: hornblende, biotite, zoisite, clino- zoisite-epidote, colorless zircon, sphene, opaque iron oxides, and very rare monazite ; thorite was not found in any of these assemblages. "When distribution of augite was discussed earlier, attention was called to the dominance of augite in the — 250 mesh fractions of sands found on beaches between the outlets of Butano, San Gregorio, and Pomponio Creeks, when ordinarily it is a relatively unimportant constituent of that size fraction. Accordingly a number of sediments cropping out near and within the drain- age areas of those streams were studied. As a result so-called sandstones reportedly belonging to the Puri- sima formation and cropping out as prominent cliffs north of the mouth of San Gregorio Creek were found to consist almost entirely of finely comminuted rhyolite glass particles (n = 1.497 - 1.503; dominantly 1.500; see George, 1924, pp. 365, 368). Furthermore, the heavy mineral assemblages separated therefrom consisted largely of euhedral grains of augite and hornblende averaging less than 62 microns in diameter. Clearly then, these pumice silts, together with contribtttions from local pillow lavas, have provided much of the fine-grained ferromagnesian constituents found in near- by sands. CALIFORNIA DIVISION OK MINES [Special Report 39 fractionation of samples of granitic rocks from the Monterey - Pacific Grove area yielded monazite with physical and chemical properties closely resembling those o!' monazite separated from neighboring sands. Thus it is suggested that the detrital monazite must owe its origin to disaggregation of local granitic rocks, a con- clusion strengthened by the knowledge that both garnet and biotite of the sands and the intrusives are strictly comparable. Thorite was not detected in residues pre- pared from any of the granitic rocks, nor in. the local beach sands for that matter. At a later date, study of the minor accessory con- stituents of the sedimentary rocks of the Coast Ranges is contemplated in order to arrive at a clearer under- standing of their mineralogy and thus to determine so far as is possible what is their contribution to local beachsands. But at this time no specific suggestions are offered concerning origin of thorite, tantalite, ehrys- oberyl, scheelite, and other minor constituents recog- nized during tins study. REFERENCES Arnott, Ronald J.. 1050, X-ray diffraction data on some radio- active oxide minerals: Am. Mineralogist, vol. 35, pp. 380-400. Bannister, F. A., and Home, J. 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