246 M^T\L<3. 



Crocidolite has a fibrous structure much resembling asbestus, and 

 has been called blue asbestus. Color lavender-blue or leek-green 

 H=4. Gr==3-2— 3-3. From Southern Africa. 



Pyrosmalite occurs in hexagonal prisms with a perfect basal cleavage, 

 and pearly surface. Color pale liver-brown, grayish, or greenish. H= 

 4 — 4 - 5. Gr=38. Contains 14 per cent, of chlorid of iron, and give* 

 off fumes of muriatic acid before the blowpipe. 



Iron-zeolite. A hydrous silicate of the oxyds of iron and manganese 

 forming incrustations at a mine near Freyberg. 



copperas. — Sulphate of Iron, or Green Vitriol. 



Monoclinic. In acute oblique rhombic prisms. M : M=» 

 92 21 ; P:M=80 37'. Cleavage parallel to P, perfect 

 Generally pulverulent or massive. 



Color greenish to white. Luster vitreous. Subtranspa- 

 rent to translucent. Taste astringent, sweetish, and metallic. . 

 Brittle. H=2. Gr = l*83. 



Composition: oxyd of iron 25*42, sulphuric acid 29*01, 

 water 45*57. Becomes magnetic before the blowpipe. 

 Yields a green glass with blowpipe ; and a black color with 

 a tincture of nut galls. On exposure, becomes covered with 

 a yellowish powder, which is a persait of iron. 



Obs. This species is a result of the decomposition of 

 pyrites, which readily affords it if moistened while exposed to 

 the atmosphere, as stated under pyrites. The old mine of 

 Rammelsberg in the Hartz, near Goslar, is its most noted 

 locality ; but it occurs wherever pyrites is found. 



Copperas is much used by dyers and tanners, on account of 

 its giving a black color with tannic acid, an ingredient in nut- 

 galls and many kinds of bark. It for the same reason form.' 

 the basis of ordinary ink, which is essentially an infusion of 

 nutgalls and copperas. It is also employed in the manufacture 

 of Prussian blue. With prussiate of potash, any soluble per- 

 sait of iron, even in minute quantity, gives a fine blue color 

 to the solution, (due to the formation of Prussian blue,) and 

 this is a common test of the presence of iron. 



About 1800 tons of copperas are used in the United States 

 annually. The colcothar of vHriol is the bro wish-red oxyd 

 of iron, obtained from copperas by calcination and other 

 processes. It is much used as a polishing powder. 



Coquimbite, or white copperas, and yellow copperas, are names of 

 wo sulphates of the peroxyd of iron. Pittizite, fibro-ferrite, are allied 



What is the appearance and taste of copperas 1 its composition 1 

 What is its origin in nature 1 For what is it used 2 



