394 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



The green silicate is most abundant in the copper area east and 

 south of Mullan. It was the most important mineral of the oxidized 

 ores of the Snowstorm mine, now largely exhausted, where it formed 

 an impregnation in quartzite and coated cracks and open spaces 

 with a translucent greenish blue botryoidal layer. In some cases 

 thicker crusts are made up of concentric and alternating layers of 

 various shades of green or blue-green and greenish-white chalky 

 material or vitreous black copper pitch. A specimen from the 

 third floor above the 800 level, east, consists in the main of green 

 chrysocolla. This is very fine grained, waxy textured and with waxy 

 to dull luster. It varies in color from green, or blue-green to robins 

 egg blue and brown-olive. The green material is overlain by com- 

 pact white material having the same texture as the chrysocolla and 

 like it, filled with contraction cracks. Under the microscope this 

 white material is nearly transparent and brownish olive-green in 

 color. The smaller pieces are isotropic while some of the larger show 

 pronounced double refraction with sweeping extinction. The latter 

 give a distinct interference figure out of the field indicating them 

 to be biaxial negative with 2V small. The average mean index is 

 1.612 to 1.618. No pleochroism was noted. In dilute acid this 

 material is not dissolved but copper is extracted. It is probably 

 one of the ciay minerals or possibly a serpentine-like substance 

 containing some copper. The chrysocolla of the specimen is like 

 that described below from the Big Elk claim. A specimen from 

 10 feet beyond the fault on the 800 foot level is rusty quartzite 

 incrusted by a pale-blue transparent minutely botryoidal crust with 

 iridescent luster. Under the microscope this is isotropic with index 

 of refraction ranging from 1.485 to 1.492. It is doubtless copper- 

 colored opal. 



A specimen from the Big Elk prospect consists largely of fine waxy 

 blue-green chrysocolla shading through olive-green into greenish- 

 brown and brown limonitic materials. Botryoidal linings of the 

 chrysocolla in cavities have a very thin outer glassy layer. Under 

 the microscope the green chrysocolla is seen mainly as a very fine 

 flaky aggregate, serpentine-like in structure, having appreciable 

 birefringence and a dirty brownish-green color in transmitted light. 

 Its mean refractive index is variable with a mean of about 1.575. 

 The outer layer is made up of transparent aggregates of exceedingly 

 fine fibers in nearly parallel position. It has a high birefringence, 

 parallel extinction and positive elongation. The indices are some- 

 what variable but a is considerably below 1.50, the exact value not 

 having been measured, while 7 is 1.570. 



Specimens from the Richmond shaft contain a little green chryso- 

 colla along with much greater amounts of copper pitch. 



