CHLORITE GROUP. 317 



schist or slate ; and they give rise also to cliloritic varieties 

 of other rocks. Moreover, chlorite is a result of the altera- 

 tion of pyroxene, hornblende, and some other iron-bearing 

 minerals ; and pyroxenic igneous rocks, like doleryte, are 

 often strongly cliloritic (as revealed by the microscopic 

 examination of thin transparent slices), in consequence of 

 this alteration — but alteration that took place before the 

 rock had cooled. Such green cliloritic material, where the 

 species is not determinable, has been called Viridite. The 

 cavities in amygdaloid are often lined, and sometimes filled, 

 by a species of chlorite, which was made from certain con- 

 stituents of the amygdaloid in the manner just stated ; and 

 the rocks adjoining trap dikes are at times penetrated by 

 chlorite made in them by means of the heat, and the mois- 

 ture contained in them or ascending with the erupted rock. 



Pyrosclerite. 



Trimetric or monoclinic. Mica-like in cleavage ; folia 

 flexible, not elastic, and pearly in lustre. Color apple-green 

 to emerald-green. H.=3. G. =2*74. 



Composition. (fMg 3 JAl) 2 12 Si 3 + 3 aq = Silica 38*9, alu- 

 mina 14-8, magnesia 34'6, water 11*7=100. B. B. fuses to a 

 grayish glass ; gelatinizes with hydrochloric acid. 



Obs. Occurs in serpentine, on Elba. 



Chonicrite {Metaxoite) is related to the above in composition, but 

 affords 12 to 18 per cent, of lime. 



Vermiculite. 



Mica-like in cleavage. Grayish, brownish, and yellowish- 

 brown in color. In aggregated scales. Also in large mi- 

 caceous crystals or plates. Laminae flexible, not elastic. 

 Lustre pearly. 



Composition. Mg 3 (Fe,Al) 12 Si 3 . When heated it exfo- 

 liates, and when scaly-granular the scales open out into 

 worm-like forms ; and thence the name, from the Latin 

 vermictdor, I breed worms ; B.B. fuses finally to a gray 

 mass. From Milbury, Mass. 



Jefferisite is a similar mineral in composition and exfoliation, occur- 

 ring in broad folia. Composition £Mg 3 *(Fe 2 ,Al 2 )O l2 Si 3 . From veins 

 in serpentine in Westchester, Pa. Culsayeeite from Culsagee, North 



