OXIhi.s 



line, topaz, and other rarer min< -nils, us wolframite, scheelite, or 

 unraninite, which have been concentrated by the same agents. 



Owing to its high specific gravity and not being affected \>\ 

 weathering, eassiterite is left behind after most of the other minerals 

 forming the rock mass have been decomposed and carried away ; 

 it is thus mechanically concentrated in the bottom of streams as 

 rolled, rounded, and water- worn pebbles (stream tin). It is from 

 these alluvial deposits that a large amount of the tin of commerce 

 is recovered. 



Little eassiterite is produced or mined in the United States ; small 

 deposits are found in Lincoln County, North Carolina ; at Harney's 

 Peak, South Dakota; near El Paso, Texas; and in the Seward 

 Peninsula, Alaska. The world's supply is derived from the Malay 

 Peninsula, Bolivia, Australia, and Cornwall, England. 



RUTILE 



Rutile. Dioxide of titanium, Ti0 2 ; Ti = 60, O = 40 ; 

 Tetragonal ; Type, Ditetragonal Equatorial ; c = .644 ; 001 A 

 101 = 32 47' ; Common forms, s (111), e (101), m (110), a (100), 

 Twinning as in eassiterite; Cleavage, 110 and 001 good; H. = 



FIG. 418. Rutile Crystals from Lynchburg, Virginia. 



6-6.5 ; G. = 4.18-4.25; Brittle, fracture uneven; Color, shades 

 of brown to nearly black ; Streak, pale brown or reddish ; Luster, 

 adamantine, metallic in appearance ; Translucent to opaque ; 

 <o = 2.615; -<a = .287; Optically (+). 



