418 PHYSIOGRAPHY. CLASS II. 



and brittle. In nitric acid it soon becomes covered with 

 a green coating. It is soluble in nitro-muriatic acid. 



2. The prismatic Nick el -pyrites chiefly occurs in veins, 

 in various classes of rocks, and is more rarely met with in 

 beds. It is almost always accompanied by octahedral Co- 

 balt-pyrites, sometimes also by ores of silver and lead. 

 The apple-green friable substance called Arseniatc of Nickel 

 or Nickel Ochre (Nickel arseniate. HAUY), found investing 

 the prismatic Nickel-pyrites, is produced by the decom- 

 position of this mineral, and consists of 37*35 oxide of 

 nickel and a little cobalt, of 36-97 arsenic acid, and 24-32 

 of water, together with a little oxide of iron and sulphuric 

 acid, according to ST no MEYER. 



3. The present species is found in veins at Schneeberg, 

 Annaberg, Marienberg, Freiberg, Gersdorf, and other 

 places in Saxony ; at Joachimsthal in Bohemia ; at Saal- 

 feld in Thuringia ; at Riegelsdorf in Hessia ; in the Hartz 

 and the Black Forest ; also at Allemont in Dauphiny, and 

 in several of the mines in Cornwall. In beds it occurs at 

 Schladming in Upper Stiria, and in the neighbourhood of 

 Orawitza in the Bannat. Mr DOEBEREINER has observed 

 that the metallic alloy, consisting chiefly of arsenic and 

 nickel, which is obtained from the process of fabricating 

 smalt, often crystallises in four-sided tabular crystals, and 

 is in every respect similar to prismatic Nickel-pyrites. 



GENUS II. ARSENICAL-PYRITES. 

 1. AXOTOMOUS ARSENICAL-PYRITES. 



Prismatic Arsenical-Pyrites. JAM. Syst. S^ol. III. p. 272, 

 Axotomous Arsenic-Pyrites. Man. p. 268. 



Fundamental form. Scalene four-sided pyramid. 

 P = 117 28', 905r, 121 58'. Vol. I. Fig. 9. AP. 



a : b : c = 1 : V ' 8 ? 4 ? : V ' 4806 - 



Simple forms. Pr (o) = 51 20' ; P + oo (d) 



