342 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



CLEARWATER COUNTY 



Black and quite well formed, though broken, crystals of tourmaline 

 up to 2 cm. in diameter occur in placer concentrates from Pierce, 

 Clearwater County (Cat. No. 87504, U.S.N.M.). The concen- 

 trates contain also corundum, epidote, garnet, etc. The tourmaline 

 is probably associated with the corundum in its original source as 

 one small crystal of tourmaline was seen embedded in a corundum 

 crystal. 



LATAH COUNTY 



In Latah County ordinary black tourmaline occurs in rough 

 crystals in the pegmatites which are mined for mica in the vicinity 

 of Avon. This mineral is also frequently abundant in bands of 

 the inclosing schist adjacent to the pegmatite masses. 65 



LEMHI COUNTY 



Tourmaline occurs abundantly in some of the ores of the Black- 

 bird district associated with cobaltite as a microscopic mineral, with 

 quartz, making up quartz-tourmaline rocks, as first determined by 

 Fran'*; L. Hess of the United States Geological Survey. Specimens 

 collected by Mr. Hess from the Haynes Stellite Co. mine on Black- 

 bird Creek, 2 miles from its mouth, in the hand specimen appear 

 as very fine grained gray masses showing no minerals distinguish- 

 able to the unaided eye except sparsely scattered large steel-gray 

 grains which have been shown by analysis to be danaite, the cobaltif- 

 erous variety of arsenopyrite. When this ore is polished, however, 

 the surface appears as a black gangue containing very abundant and 

 extremely minute reddish gray metallic particles of cobaltite. The 

 black gangue is quartz-tourmaline rock. When this ore is powdered 

 to pass a 200 mesh sieve the constituent grains of the fine aggregate 

 are separated and under high magnification appear as sharply 

 octahedral or cuboctahedral crystals of the opaque metallic mineral 

 and grains of quartz and tourmaline. The tourmaline forms either 

 equidimensional irregular grains or very stout prisms, the elongation 

 twice the diameter or less. It is strongly pleochroic, e = very pale 

 \iolet brown to brownish gray, w = deep gray-blue. The refractive 

 indices measured are e = 1.635, u = 1.658. 



A second specimen from this district, exact locality unknown, 

 possibly from the same mine, is black in the specimen and is visibly 

 coarser grained and sparkling. This is coated along cracks with 

 beautiful rose-red erythrite. Under the microscope it consists of 

 quartz and tourmaline like the last. Wnile coarser grained the 

 tourmaline is identical in color pleochroism and refractive indices. 



A specimen labeled gabbro-porphyry from the west end of the 

 Beliel group is medium fine granular and micaceous in appearance 



•» Douglas B. Sterrett. U. S. Oeol. Survey, Bull. 740, pp. 86-93, 1923. 



