THE MINERALS OF IDAHO 



201 



in size from small rounded grains to pebbles a half inch or more in 

 diameter. The tin pebbles as they occur on Panther Creek are 

 sparsely distributed through the lower portion of a bed of gravels 

 which varies from 4 to 20 feet in thickness. 



A specimen (Cat. No. 86,809, U.S.N.M.) in the National Museum 

 is labeled: "Stream wood tin from Prairie Basin, Lemhi County." 

 It consists of waterworn pebbles up to 1.5 cm. in size, of wood tin 

 having the usual radiate fibrous structure and varying colors from 

 pale brown to dark brown, red brown, and black. 



OWYHEE COUNTY 



Cassiterite has been found in the Silver City district in placers. 

 It is the variety known as wood tin and occurs in beautifully rounded 

 masses from one-eighth to one-half inch in diameter. 

 It was especially noted along Jordan Creek. llc 



SHOSHONE COUNTY 



Stream tin is reported to occur in the Coeur d'Alene 

 district. 11 ^ 



RUTILE (250) 



Titanium dioxide, Ti0 2 (or titanyl titanate, TiO.Ti 2 3 ). 



Tetragonal. 



BOISE COUNTY 



Rutile has been noted sparingly in black sands from 

 a number of gold placers in Idaho. A steely lus- 

 tered prismatic crystal 6 mm. long, found in the 

 polycrase-bearing sand from Centerville, was iden- 

 tified as rutile. The prismatic zone is deeply striated, 

 the forms present being a(100), m(110), and 2(130). 

 The crystal is terminated by the pyramid c(011). 

 This crystal is shown in the drawing (fig. 36). It 

 was peculiar in showing greenish internal reflections 

 and when crushed and examined in transmitted light 

 the color was yellowish green, a very unusual color 

 for rutile. As emphasized under "zircon," some of the light colored 

 crystals which have been described as that mineral may be rutile, 

 the angles of rutile and zircon being so similar that very accurate 

 measurements are necessary to distinguish between them. 



Fig. 36.— Rutile. 

 Crystal from 

 coarse placer 

 concentrate. 

 Centerville, 

 Boise County 



"« Browne and Taylor. W. P. Blake, Mineral Resources of United States, L866, i>. 201. 

 "<* U. S. (Icol. Survey, Hull. (124, p. 115, 1917. 



