THE MINERALS OF IDAHO 



415 



of the gravel. It seems to be more plentiful in the ancient gravels 

 than in the recent. Several partial analyses of nonmagnetic portions 

 of concentrates from Musselshell Creek gave the following results: 



Partial analyses oj monazite concentrates 

 [R. C. Wells, analyst] 



Phosphoric acid (P2O5)- 

 Thona(Th0 2 )---- 



(1) 



10.90 

 1.20 



(2) 



8.yo 



1.15 



(3) 



15.50 

 1.85 



(4) 



8.70 



Computation from the content of phosphoric acid shows that the 

 analyzed samples range from 32 to 55 per cent of monazite. When 

 cleaned to about 90 per cent monazite, the usual commercial grade, 

 these sands average about 3 per cent Th0 2 . On a basis of pure 

 monazite the thoria content would be about 3.3 per cent. 



OTHER LOCALITIES 



Monazite has been reported as occurring in similar manner in 

 placer sands in a large number of localities in Idaho. Specimens 

 from these localities have not been available for examination by the 

 present writer. The mineral is to be expected in most of the gold 

 districts in the central Idaho granitic area. 



APATITE (549) 



Hexagonal, hemihedral. 



Calcium chloro- and fluo-phosphate, 

 9Ca0.3P 2 5 .Ca(F,Cl) 2 . 



The calcium phosphate apatite has been noted only from Lemhi 

 County, although it probably is not so rare in the State as this might 

 indicate. 



LEMHI COUNTY 



A specimen from the Togo claim, Blackbird district, contains dull, 

 yellowish rough tabular crystals of apatite up to 1 cm. in diameter 

 associated with green rosettes of chlorite in cavities in schist. Opti- 

 cally the apatite is biaxial and negative with 2V very small. The 

 refractive indices are a = 1.630, (3 = 1.640, 7= 1.643. The mineral is 

 easily soluble in 1 :1 nitric acid and the solution reacts for phosphoric 

 acid. 



Another specimen from the Haynes Stellite mine, in the Blackbird 

 district, contains long slender white prisms of apatite embedded in 

 quartz and associated with cobaltite. As shown in the photograph 

 of this specimen reproduced in Plate 6, lower, the apatite prisms are 

 broken into sections and the fractures are filled with dark-colored 

 mica or chlorite. 



