454 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



The lowest index, 1.818, is also that of linarite, while the other 

 indices are much higher than 1.82, the highest immersion oil avail- 

 able. Under the microscope the mineral is pale green and no pleo- 

 chroism could be noticed. 



BROCHANTITE (740) 



Basic copper sulphate, 4CuO.S0 3 .3H 2 0. Orthorhombic. 



The basic copper sulphate brochantite greatly resembles malachite 

 in color and general appearance and may frequently be confused with 

 the carbonate. It has been definitely identified in Idaho in the local- 

 ities mentioned below and probably occurs elsewhere. 



ADAMS COUNTY 



The first recognition of brochantite in Idaho was by Palache,' 4 who 

 noted it in specimens from the Seven Devils district as slender 

 transparent emerald-green prisms and radiating 

 fibrous aggregates interspersed among epidote 

 crystals. A number of specimens of this mineral 

 from this district have been seen. A specimen 

 from the Badger claim contains the basic sulphate 

 as green crystalline films on joints and fractures. 

 The specimen contains no measurable crystals. 

 A specimen from the South Peacock mine con- 

 tains small emerald green crystals in cavities in 

 a mass of quartz and specularite. These are short 

 prisms showing the prism ?/i(110) and the pina- 

 coid 6(010) . The terminations are dull and show 

 no faces. Measurements of the prism zone give 

 an angle of 75° 39' for the prism which agrees 

 with the angle m: m" ' for brochantite which is 

 75° 28'. The mineral dissolves in hydrochloric 

 acid without effervescence and reacts strongly 

 for sulphate with barium chloride. 



BANNOCK COUNTY 



A specimen in the National Museum (Cat. No. 

 75521) labeled as from Pocatello, Bannock County, 

 consists of chalcocite partly altered to an emerald 

 green mineral, in a chalky-appearing whitish rock. 

 The green material is brochantite. A small crys- 

 tal from this locality which was measured was 

 bounded by the prism m ( 1 1 0) , the pinacoid 6(010) 

 and the base c(001) which was dull, with the 

 habit shown in Figure 158. The angle for the prism average 

 76° 20' while the corresponding angle for brochantite is 75° 28'. 



Fig. 158.— Brochantite. 

 Pocatello, Bannock 

 County 



H Charles Palache. Amer. Journ. Sci., vol. 8, p. 302, 1899. 



