330 MINERALOGY 



commercial supply of the potassium salts of the world is at present 

 obtained ; for this reason they are most important, as potassium 

 is one of the few elements required by all soils to produce good 

 crops, and must be imported by all nations, as a fertilizer, to add 

 to the soil when the original supply of potassium has been exhausted. 

 It is also used in the production of niter (KNO 3 ) from Chili 

 saltpeter, which is the oxidizing agent in gun and blasting powder. 



CERARGYRITE 



Cerargyrite. Horn silver ; Silver chloride, AgCl, Ag = 75.3, Cl 

 = 24.7; Isometric; Type, Ditesseral Central; Forms, a (100), 

 d (110), o (111) ; Twinning plane o ; Cleavage, none; Highly 

 sectile; H. = 1-1.5; G. = 5.55; Color, white gray to brown; 

 Darkens on exposure to light; Luster, resinous to adamantine; 

 Transparent to opaque; n = 2.61. 



B.B. On coal fuses easily, yielding globules of metallic silver. 

 In the S. Ph. bead saturated with copper oxide yields an azure 

 blue flame (Cl). Insoluble in acids, but soluble in ammonia. 



General description. Crystals are rare, but cubic in habit ; 

 it occurs more often massive, disseminated, or in crusts and 

 dendritic. 



The best specimens have been obtained from Peru, though good 

 crystals are found in the Poor Man's lode in Idaho. Cerargyrite 

 is an important ore of silver at the Comstock lode, Nevada; 

 Leadville, Colorado, and Cobalt, Ontario. It is common in veins, 

 associated with galena, native silver, barite, calcite, and quartz, 

 especially in the superficial portions, where it is formed as a second- 

 ary mineral. Soluble silver sulphate is formed by the oxidation 

 of sulphides, arsenides, or antimonides, and is then precipitated by 

 contact with chlorides or by the intermixing with other solutions, 

 containing chlorides. 



Cerargyrite has been produced artificially by the slow diffusion, 

 through a diaphragm of asbestos, of solutions of sulphate and 

 chloride of silver. 



Bromyrite, AgBr, iodyrite, Agl, and embolite, Ag(ClBr), are very 

 similar to Cerargyrite, both in appearance and association. Iodyrite 

 is interesting as an example of dihexagonal polar symmetry. They 

 are all valuable ores of silver. 



