246 EEPORT OF NATIONAL MUSEUM, 1899. 



luster metallic-adamantine, opaque as a rule, rarely transparent; color, 

 reddish brown to red, rarely yellowish, blue, or black; streak, pale 

 brown. The mineral crystallizes in. the tetragonal system, and is 

 commonly found in prismatic forms longitudinally striated (Specimen 

 No. 14410, U.S.N.M.) and often in geniculate or knee-shaped twins 

 (Specimen No. 81904, U.S.N.M.). Not infrequently it occurs in the 

 form of fine thread-like or acicular crystals penetrating quartz. It is 

 insoluble in acids and infusible. 



Mode of occurrence. Kutile occurs mainly in the older crystalline 

 granitic rocks, schists, and gneisses, but is also found in metamorphic 

 limestones and dolomites, sometimes in the mass of the rock itself, or 

 in the quartz of veins. Being so nearly indestructible under natural 

 conditions, it gradually accumulates in the debris resulting from rock 

 decomposition, and is hence not an uncommon constituent of auriferous 

 sands. 



Localities. Some of the more noted localities are, according to 

 authorities, the apatite deposits of Kragero, in Norway; Yrieux, near 

 Limoges, in France; the Ural Mountains; and the Appalachian regions 

 of the United States. Graves Mountain, Georgia (Specimen No. 

 46081, U.S.N.M.); Randolph County, Alabama (Specimen No. 65354, 

 U.S.N.M.); and the Magnet Cove region of Arkansas are celebrated 

 localities. 



Uses. Like ilmenite, the mineral may serve as a source for titanium 

 for a pigment for porcelain, but as yet it is little used. 



Brookite (Specimen No. 45256, U.S.N.M.) and octahedrite have the 

 same composition and essentially the same physical properties and 

 mode of occurrence. 



9. CHROMITE. 



Chromite is a mineral of the spinel group, and of the theoretical 

 formula FeO, Cr 2 O 3 . This equals a percentage of chromic oxide of 

 68 per cent, but the natural mineral has often alumina and ferric iron 

 replacing a part of the chromium, so that 50 per cent chromic oxide 

 more nearly represents the general average. The ordinary demand, 

 it may be stated, is for an ore carrying 45 per cent and upward of 

 chromic acid. 



