PHYSIOGRAPHY. CLASS II. 



a clean surface of iron or zinc. It is insoluble in nitric 

 acid or in water. It may be obtained in a crystallised 

 state, either from fusion, or from the evaporation of a 

 solution of muriate of silver in ammonia. 



2. The present species is most frequently found in the 

 upper parts of veins in clay-slate, but occurs also in beds, 

 generally along with other ores of silver, very often also 

 with ochry varieties of prismatic Iron-ore, or with similar 

 varieties of decomposed Iron-pyrites. Sometimes, though 

 as it seems not in veins, hexahedral Gold is found accom- 

 panying it. It is associated also with several species of the 

 orders Malachite, Pyrites, Haloide, Baryte, &c. 



3. Formerly it occurred in considerable quantities in the 

 Saxon mining districts of Johanngeorgenstadt and Frei- 

 berg ; also at Joachimsthal in Bohemia. In small quanti- 

 ties it is found in France, in Spain, at Kongsberg in Nor- 

 way, in Cornwall, and Siberia ; but in large masses, fre- 

 quently associated with hexahedral silver, in Mexico and 

 Peru, where particularly the green varieties of colours occur. 



4. It is used for extracting silver. 



$. PYRAMIDAL PEARL-K.ERATK. 



Pyramidal Corneous Mercury. JAM. Syst. Vol. II. p. 356. 

 Man. p. 91. Muriate of Mercury. PHILL. p. 359. 

 Quecksilber-Hornerz. WERN. Hoffm. H. B. III. 2. S. 25. 

 Hornquecksilber. HAUSM. III. S. 1017. Quecksilber- 

 Hornerz. LEONH. S. 191. Mercure muriate. HAUY, 

 Traite', T. III. p. 447. Tabl. comp. 78. Traite', 2de Ed. 

 T. III. p. 331. 



Fundamental form. Isosceles four-sided pyramid. 



P = 98 4', 136 V. Vol. I. Fig. 8. BROOKE. 

 Simple forms. -^- P 3 (a) = 138 IV, 60 1 1' ; 



-^ P 2 (c 1 ) ; P (c 2 ) = 126 31', 79 3'; 



Char, of Comb. Pyramidal. 



Combinations. 1. P. [P + oo]. Sim. Fig. 97. 



