S2 DE. THOMAS STEREY HUNT ON THE 



physical characters. It includes what has been variously designated as pinite, gieseckite, 

 agalmatolite, and dysyntribite, which sometimes occur in crystalline forms in other rocks, 

 and at other times themselves constitute rock-masses. Amorphous, and grauixlar or com- 

 pact in texture, its hardness and general aspect have often led observers to compare it to 

 serpentine. The many varieties of this substance, as Dana has remarked, agree closely 

 in physical characters, as well as in composition, and he has deduced from their analyses 

 a formula corresponding to a hydrous silicate of potash and alumina, with the ratios, 1 : 8 : 

 12 : 3, which rec^uires potash 12.0, alumina 35.1, silica 46.0, water 6.9 = 100 ; in which 

 the potash may be partially replaced by soda, lime, or magnesia. Dysyntribite, as first 

 described by C. U. Shepard, forms rock-masses, associated with specular hematite in St. 

 Lawrence county. New York ; and similar deposits, often of considerable extent, occur in 

 the crystalline schists of the Grreen Mountain range, both in Vermont and Quebec. In ihe 

 latter province, a bed of it in Stanstead, interstratified with chloritic schists, is one hundred 

 feet wide, schistose, and often with an admixture of quartz. Layers of the pure pinite 

 from this deposit, formerly described by the writer under the synonym of agalmatolite, have 

 a banded structure, a ligneous aspect, and a satiny histre. The mineral is translucent, 

 soft, unctuous, and somewhat resembles steatite. A similar deposit occurs in argillite, 

 among the crystalline schists of St Francis, Beauce, which is honey-yellow in colour, 

 and granular in texture. The piuites from these two localities agree closely in composi- 

 tion. That of the latter contained silica 50.50, alumina 33.40, magnesia 1.00, potash 8.10, 

 soda 0.63, water 5.36 (with traces of lime and iron-oxyd) = 98.99. These elements give 

 almost exactly the oxygen-ratio of 1 : 8 : 13} : 2J, closely agreeing with Dana's formula, 

 except in an excess of silica perhaps due to an admixture of quartz, which is apparent in 

 the dejjosit at Stanstead.''- The variety of pinite, formerly described as parophite from its 

 resemblance to serpentine, occurs in uncrystalline Cambrian shales at St. Nicholas, near 

 Quebec.^' Related to pinite are the minerals which have been called onkosine and oosite. 

 The name of cossaite has been given to a similar mineral having the physical charac- 

 ters of pinite, from which it differs in containing soda instead of potash. The formula, 

 which has been deduced from its analysis, is identical with that of the soda-mica, para- 

 gonite. We cannot be certain, in the case of massive minerals like these, whether this 

 same general formula is not as well adapted to pinite as that proposed above. In any case, 

 it is evident that we have in the pinitic group a widely distributed class of natural sili- 

 cates, not less important than the muscovitic group, and probably similar in origin. 



'* See, for an account of these various forms of pinite, tliere described as agalmatolite, the Geologj' of Canada, 

 1863, pp. 4S4, 485. 



"' There are several other hydrous silicates of alumina, sometimes with alkali, -nhicb, like pinite, are 

 sometimes found among uncrystalline strata, showing that the conditions of their deposition have been continued 

 down to comparatively recent times. Such is the bravaisite described by Mallard, a soft unctuous matter, with a 

 fibrous texture, occurring in layers in shales of the coal-measures in France. It is a hydrous silicate of potash and 

 alumina, with a little lime and magnesia, and according to its author, after deducting impurities, gives essentially 

 the ratios, 1:3:9:4. The hygrophilite of Laspeyres is also a soft imctuous cryptocrystalline matter, found in 

 sandstone, which somewhat resembles bravaisite, and is compared to pinite. It contains potash and some sodai 

 and gives the ratios, 1:5:9:3. A somewhat similar substance, found replacing coal-plants in the Taren- 

 taise, has been also referred to pinite or to the so-called gumbellite. Genth, on the other hand, found pyrophyllite 

 replacing the substance of coal-plants in Pennsylvania. (See Dana's System of Mineralogy, Supplements, I. G; 11. 

 29, 63; and III. 18, 54). 



