272 



ECONOMIC GEOLOGY 



3,000 C.; its specific gravity is 3.543, and its atomic weight is 

 48.1. 



Mode of Occurrence. Titanium is often catalogued as one 

 of the rarer elements; yet it is almost invariably present in the 

 igneous rocks, and in the sedimentaries derived from them. 

 According to F. W. Clarke, out of 800 igneous rocks analyzed 

 in the laboratory of the U. S. Geological Survey, 784 contained 

 titanium. It is found in nature only in the oxidized state (Fig. 

 133). 



Olirine-hyperite 



Hornblende Rock 



01 i vine- hype rite. 



i iiimiiimiiiiiiiiiiiiiiiiiiiiiiiimmummi 



FIG. 133. Titaniferous apatite vein in gabbro. (After J. H. L. Vogt.) 



Ores of Titanium. Ilmenite, FeO, Ti0 2 , is a faintly magnetic 

 iron-black mineral, with a black or brownish-red streak. Several 

 varieties have been recognized, based on the relation of the iron 

 to the titanium. The true ilmenite carries from 26 to 30 per cent, 

 of titanium. Menaccanite carries from 20 to 25 per cent, of 

 titanium. 



Leucoxane is a metamorphic decomposition-product of ilmenite 

 and its numerous varieties. It occurs as a white or reddish 

 mineral surrounding ilmenite. 



Rutile, TiO 2 , shades in color from reddish-brown to black. 

 It occurs in tetragonal crystals, often twinned. 



