OXIDES 



351 



\ :i secondary mineral rutile i> derived from octaliedrite ;ind 

 tnrniing pseudomorphs after the latter, as at Magnet 



Fn, r_'0. Rutile Crystals from Graves's Mountain, Georgia. The Upper Twins 



are from the Tyrol. 



Cove, Arkansas. These three minerals are all dioxides of titanium, 

 in different phases, and are quite often associated ; rutile has the 

 highest specific gravity and is the stable form at high tem- 

 peratures. Octahedrite is also of tetragonal symmetry, while 

 brookite is orthorhombic. 

 Rutile may also be formed 

 in the alteration of ilmenite 

 and titanite, which process 

 is reversed in the alteration 

 of rutile. 



Chemically rutile gener- 

 ally contains iron, to which 

 the red or brown color is 



due; the iron content is 

 considerable in some cases 

 and massive rutile may 

 grade gradually into ilme- 

 nite. 



Commercially rutile is the source of titanium salts, which are 

 used as a yellow coloring agent in porcelain and to obtain the ivory- 



FIG. 421. Brookite froifi 

 Arkansas. 



Magnet Cove, 



