THE NONMETALLIC MINEEALS. 403 



due merely to oxidation they need not be taken into consideration 

 hero. When crystallized, the mineral assumes octahedral and dodeca- 

 hedral forms, more rarely cubes. Hardness 5.5, specific gravity 9 

 to 9. 7. Color grayish, greenish to velvet black, streak brown; fracture 

 conchoidal, uneven. The massive and probably amorphous variety, 

 containing few, if any, of the rarer earths and no nitrogen, is known 

 under the name of pitchblende. This last is the chief commercial 

 source of uraniimi salts. Through oxidation and hydration the min- 

 eral passes into gummite, a gum-like yellow to brown or red mineral of 

 a hardness of but 2.5 to 3 and specific gravity of 3.9 to 4.2. (See Speci- 

 men No. 53062, U.S.N.M., showing zone of gummite around a nucleal 

 mass of unaltered uraninite.) 



Localities and mode of OGGurrence. — Uraninite occurs as a primary 

 constituent of granitic rocks and as a secondary mineral, with sulphide 

 ores of silver, lead, gold, copper, etc. In this form, according to Dana, 

 it is found at Johanngeorgenstadt, Marienberg, and Schneeberg, 

 Saxon}' ; at Joachimsthal (Specimen No. 53061, U. S. N. M. ) and Pribram, 

 in Bohemia (Specimens Nos. 66843, 67755, U.S.N.M.), and Rezbanya,in 

 Hungary. Considerable quantities have been mined from the tin- 

 bearing lodes of Cornwall, England. The crystallized variety hrog- 

 gerite is found in a pegmatite vein near Annerod, Norway, and the 

 variety cleveite in a feldspar quarry at Arendal. In the United States 

 the mineral has been found in small quantities in several localities, but 

 only those of Mitchell and Yancey Counties, North Carolina (Speci- 

 mens Nos. 53062, 60927, 62755, U.S.N.M.), where the mineral occurs 

 partiall}^ altered to gummite and uranaphane, in mica mines; Llano 

 County, Texas; Black Hawk, near Central City, Colorado (Specimen 

 No. 83629, U.S.N.M.), and the Bald Mountain district of the Black 

 Hills of South Dakota need here be mentioned. Of the above the 

 Cornwall localities are at present of greatest consequence, having 

 during 1890 yielded some 22 tons of ore, valued at some £2,200 

 (111,000). During 1891, it is stated, the output was 31 long tons, 

 valued at £620, and in 1892, 37 tons, valued at £740. The next most 

 important locality is that of Joachimsthal, in Bohemia, where 22.52 

 metric tons of ore were produced in 1891 and 17.71 tons in 1892, the 

 value being some 1,000 florins a ton. 



In the Cornwall mines the pitchblende is stated^ to occur in small 

 veins crossing the tin-bearing lodes. At the St. Austell Consols 

 Mines it was associated with nickel and cobalt ores; at Dolcoath with 

 native bismuth and arsenical cobalt in a matrix of red quartz and pur- 

 ple fluorspar; at South Tresavean with kupfer-nickel, native silver, 

 and argentiferous galena. At the Wood Lode, Russell district, in 

 Gilpin County, Colorado, pitchblende was found in the form of a 



^The Mineral Industry, II, p. 572. 



