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Maps, platea. charts, etc.. may be filmed at different reduction ratioa. Thoae too large to be entirely included in one expoaure are filmed beginning in the upper left hand comer, left to right and top to bottom, aa many framea aa required. The following diagrama illustrate the method: Loe cartea, planches, tableaux, etc., pauvent itre filmte i dee taux de rMuction diff Arents. (.orsque le document est trop grand pour dtre reproduit en un seui ciichi, ii eat film4 A partir de Tanglo supAriaur gauche, de gauche i droite. et de haut en baa. an prenant le nombre d'imagtoa nteaaaaire. Lea diagrammea suivants iilustrsnt la m4thodo. 1 2 3 1 2 3 4 5 6 .■A\ ■^■:^t PA ■I '^»*rki*j;^ THE COMPOSITION OF DAWSONITE. n, ' ■- ,r /%•:•:■■- v>' »V B. J. HA.EHtNGfTON,,B.A., PHiD. ' ■■■ ... \' ' mm''. '/■OV, *' ■■ ■ ^ i-. -. ^-r ':'-J.\ •■S'^A w [f ' . ' '4; + • J ■'*.- t^l >^'.5.. :.•:>* ./;C^^^■-^' •a^; {From the Canadian Naturalist, Vol. X, No. 2 — 1881.) HV NOTE ON THE COMPOSITION OF DAWSONITE. By B J. Haurinoton, B.A., Pii.D. Mc(!ill College, Montreal. In connection with tlio discoveries of Diiwsonite which have been m.ide at Piiin Ca.stairn.iio in Tuscany,* a lew remarks on the composition of this curious uiineral ni.iy be deemed of interest. It will be remembered that the specimens originallydescribed in 1874 were from joints in a white fehispatliic dyke cutting the Trenton limestone near McGill College. f Since 1874 small quan- tities of the mineral have been observed in the joints of several other dykes in the same neighbourhood, and beautiful specimens have been obtained at the Montreal reservoir, in what is probably a continuation of the dyku ne.ir the college. In the latter in- stance the Dawsonite is associated with calciie, dolomite, pyrite, mil ute quantities of galena and occasionally of a black substance rich in manganese. In all cases the mineral occurs in more or less fibrous bl.ides, which are often arranged in a radiated manner. It reminds one of tremolitc, and in the collection of miner.ils acquired by McGill College from the late Dr. Holmes of Mont- real, there are several specimens of it which he had so marked. The first specimens of Dawsonite analysed were found to con- tain between five and six per cent, of lime, and there was no evidence to prove that this w.is not one of the proper constituents of the mineral. Subsequently, however, it was found that the proportion of lime differed widely in different c.ises, while the ratio between the other constituents was constant. From this it • Two papers on the > ubjeet liave appeared within the last few months in the Bulletin of tlie Minenilogieal Society of France (IV., 28 and l,o5), the first, entitled " Sur nn nouvviaii gi.senicnt de Daw- sonite (hydrocarbonate d'aluminum et de sodium) et sur la formule de ce mineral," by C. Friedel ; the second, "Sur le gisoment de la Dawsoijite de To.^can^e," by Maurice diaper. t Can. Nat. II. vu. 305. '• Notes on Dawsonite, a new Carbonate." fT 9 itt|(*. I (i^ » • • » ' r * * ' , ltt«' •!••' 2 was inferred that the lime yoiiUy bt.-longed to intermixed culcite wliich could not be complett-ly sepiratod. This view is fully confirmed by Friedel's examination of the Duwsonite discovered by M. Maurice Chaper in Tuscany, and the riyht of the mineral to rank as a good species may now be considered as fully estab- lished. Its special interest of course depends upon tiie fact that it is the only well deliiied carbonate containing aluminium which has yet been met with in nature. The Tuscany Dawsonite is stated to occar in minute crevices, both in marl and "atidstone, the latter being impregnated with dolomite. Among the minerals as:*ociated with it are calcite, dolomite, pyrite, fiorite and cinnab.r; and it is said that the miners of the region look upon Dawsonite as a favourable indica- tion in their search for cinnabar. The Tuscany mineral is evidently obtained in a purer condition than ours, and from hia analyses Friedel concludes that the eompi^sition of the species is represented by AI2O3, NajO, 2 COj, 2 ll^O or, as he also puts it, AI2 (C03Na)2 (011)4. The following table gives under I. the results of Friedel's an- aJ alyses ; under II and III the original analyses of the mineral ■ frum McGill College ; and under IV a recent one of that found at the Montreal reservoir. The lasi,it will b^ scen,indicates the presence of a large proportion of calcite : — I II III IF Carbon dioxide 29.59 29.88 30.72 32 23 Alumina 3.5.89 32.84 32.68 24.71 Soda 19.13 20.20 20.17 15.64 Water 12.00 11.91 (10.33) 9.06 Lime 0.42 5.95 5.65 1G.85 Magnesia 1.39 tr. 0.45 tr. Potash 0.38 Manganese dioxide . • • • 0.23 Silica 0.40 .... 0.84 98.42 101. 5P 100.00 99.56 If from the above analyses we deduct the substances which may justly be regarded as impurities, including lime and mag- nesia in the form of carbonates, and then calculate the normal constituents for one hundred parts, it will be seen that the re- sults agree well with the formula Naj [Alj] C-zO^ + 2H2O : t .« • . • • • . • • • • • • • • • • • k 'c • « 3 I II III IV Formula. Carbon dioxide* ... . 29.27 27.96 29.06 27.78 30.49 Alumina 37.88 36.42 36.70 36.12 35.55 Soda 20 19 22.41 22.65 22.86 21.48 Water 12,66 13.21 11.59 ]3.24 12.47 It has also been suggested that the formula may be written SCNa^COa) + (Al^CgO,) + 2(He[Al JOe).t According to Priedel, the Tuscany Dawsonite when heated to 180*^ C. lo.scs nothing but a little hygrometric water. Like the Canadian mineral it gives up both its " carbonic acid " and water at a red heat. The calcined '•'■sidue also dissolves easily in hydrochloric acid. Neither the hardness nor the specific gravity of the European variety has been ascertained. For the Canadian mineral the original determinations were, H = 3, G = 2.40. • The atomic ratios for I and II are as follovvs : C 665 .636 [Alg] 369 .355 Na 651 .723 2.764 2.696 ^2 I 703 .734 t Am. Jour. Sci. III. x.xii. 157.