THE MINERALS OF IDAHO 



273 



The specific gravity of the analyzed sample was found to be 2.54 

 (orthoclase = 2.57, Dana). A determination of alkalies in a specimen 

 from the Trade Dollar vein gave George Steiger: Potash K 2 14.95 

 per cent, Soda (Na 2 0) 0.20 per cent. Another specimen from the 

 same vein in basalt gave K 2 0, 13.56 per cent. 



In thin section the valencianite has the characteristics of orthoclase 

 the index of refraction, a little lower than that of quartz, helping to 

 distinguish it from that mineral. The crystals and grains are single 

 individuals and many of the larger ones show optical anomalies 

 probably due to pressure. 



In addition to Lindgren's specimens, several collected more 

 recently by E. L. Jones, jr., of the United States Geological Survey, 

 have been examined. A specimen from the 

 Blaine tunnel dump consists of a fine flat 

 crust of white to colorless crystals of rhombic 

 aspect reaching 7 mm. maximum diame- 

 ter, coating a fissure in altered igneous 

 rock. A specimen from a raise 1,300 feet 

 from the portal of the Blaine tunnel con- 

 sists of altered rock fragments cemented by 

 a granular quartz-adularia aggregate con- 

 taining finely disseminated silver sulphides 

 and chalcopyrite. Drusy cavities in this 

 specimen are lined with well-formed crys- 

 tals of colorless adularia up to 5 mm. in 

 diamater associated with small slender 

 quartz crystals. A specimen from the ore 

 bin of the Silver City mine consists largely 

 of coarse granular white valencianite in- 

 tergrown with quartz with small valencianite crystals of the usual 

 habit in cavities. Another specimen from a tunnel dump on the 

 south side of Long Gulch below the Blaine tunnel consists of frag- 

 ments of altered and epidotized igneous rock cemented by quartz 

 combs bearing curved and striated valencianite crystals up to 2 

 cm. in diameter. Some fluorite rests upon the valencianite. 



The simple habit which characterizes the cystals from most of the 

 specimens which show only the prism (110) and the negative dome 

 (T01) is illustrated in Figure 72, which brings out the strikingly 

 rhombohedral aspect of the crystals. In Figure 73 is shown a twin on 

 (100), the Carlsbad law. The crystal illustrated in Figure 74 shows 

 also the base (001). The prism faces are greatly striated vertically 

 and are always curved yielding poor measurements and (101) and 

 (001) are striated horizontally by oscillation. A crystal of the habit 



Fig. 74— Orthoclase (adula- 

 ria) SHOWING FACE OF P(001). 



Silver City district 



