SILICATES, TITAN ATI'S, ETC. 505 



Tit unite as a pyrogenetic accessory mineral is very widely dis- 

 tributed in :ill 'mucous rock-, except those rich in silica and mag- 

 iii -i. i. As a metamorphic mineral it occurs in the schists and crys- 

 talline limestones, when- it is associated with such minerals as 

 apatite, M-;ipolite, zircon, hornblende. Especially fine crystals 

 occur in a limestone at Etenf rew County, Ontario. In the United 

 States it occurs at numerous localities in the Atlantic coast states. 



At St. Gothard, Switzerland, clear honey-yellow crystals occur, 

 associated with adularia. 



Alteration products of titanite are not common. At times it 

 forms perovskite, CaTiO 3 , an isometric mineral crystallizing in cubes 

 and octahedrons; by the elimination of both calcium and silica, 

 rut He and octahedrite have' been noted as being formed from 

 titanite. I'm lor favorable conditions the reverse of this may occur 

 and titanite re.-ult from rutile or octahedrite, and especially from 

 ilmenite, when the alteration product is known as leucoxene. 



The synthesis of titanite has been effected by the simple fusion of 

 its chemical constituents, at a temperature of 1400. If the melt is 

 low in silica, perovskite will form. 



Benitoite, BaTi(SiO 3 )s, a titanosilicate of barium, is an interest- 

 ing mineral, as it represents the ditrigonal equatorial type, which up 

 tot he time of its discovery had no representative. It occurs in San 

 Benito County, California, imbedded in a vein of massive natrolite 

 and associated with another rare titanium mineral, neptunite, 

 (Na.K) 2 (Fe.Mn)(Si.Ti) 5 Oi2, heretofore only found at Narsarsuk, 

 Greenland. 



COLUMBITE 



Columbite. (Fe . Mn) (CbO 3 ) 2 ; a columbate of iron and man- 

 ganese; Orthorhombic ; Type, Didigonal Equatorial; a:b:c = 

 .8285 : 1 : .8897 ; 100 A 110 = 39 38'; 001 A 101 = 47 2'; 001 A 

 Oil == 41 40'; 001 A 111 =54 21'; 001 A 133 =43 48'; Common 

 forms, a (100), b (010), c (001), m(110), o(lll), u (133), k(103); 

 Twinning plane, 021, contact and heart-shaped twins common; 

 Cleavage, a distinct, b less so ; Brittle ; Fracture, uneven ; H. = 6 ; 

 G. = 5.3-7.3 ; Color, iron-black to brownish ; Streak, dark red to 

 1'lack ; Luster, submetallic, brilliant to resinous ; Opaque, at times 

 iridescent. 



B.B. Infusible or fuses with great difficulty. The S. Ph. 

 bead saturated and reduced with tin on coal, then dissolved in a 



