448 NATURAL HISTORY. 



air and water find admittance. The old mines of Hartz, 

 Tyrol, and Black Forest, is its most noted locality, but 

 always found near pyrites. Copperas is used for making 

 ink, and in dyeing and tanning. Employed also in the 

 manufacture of Prussian Blue, Oil of Vitriol, and med- 

 icinally. 



Blue Vitriol Sulphate of Copper. Found usually 

 in incrustations or in the stalactitic overflowing of waters 

 passing through copper mines ; also exhibited on rocks. 

 Structure crystal-like, luster vitreous ; color deep sky- 

 blue, verging into greenish ; taste, astringent, nauseous, 

 and metallic. Dissolves readily in water ; if iron is put 

 into the water, the metallic portion of the copper falls to 

 the bottom. Found sometimes in old copper mines, at 

 others it is obtained from copper springs, in the waters 

 of which iron bars were deposited ; the copper springs 

 of Wicklow, Ireland, and the Rio Tinto mine in Spain, 

 are the principal localities where copper is worked in so- 

 lution. H. = 2.5. G. = 2.2 to 2.3. Used in color- 

 ing, in preparing paints, and also in medicine. 



THIRD CLASS. 

 COMBUSTIBLE MINERALS. 



This family of minerals is distinguished by a combus- 

 tible nature, and consists of substances that burn read- 

 ily, sometimes with a resinous flame, at others rather 

 pale blue sulphurous light, which arises from the decom- 

 position of the water present, and the formation of the 

 gas called carbonic oxyd. 



