346 MINERALOGY 



Hematite is also formed, as in the lavas of Vesuvius, by decom- 

 posing the vapors of ferric chloride with steam. 



Arsenic, antimony, and bismuth form anhydrous sesquioxides 

 which are found as minerals, but only in small quantities and 

 restricted in distribution. Those of arsenic and antimony are 

 isomorphous and dimorphic. Arsenolite, As 2 O 3 , occurs at the Ophir 

 mine, Nevada, and appears as white crusts on native arsenic. 

 Senarmontite, Sb 2 O 3 , is formed as a coating on stibnite. Both are 

 isometric, crystallizing in octahedrons. 



Claudetite, As 2 O 3 , and valentinite, Sb 2 O 3 , are both formed by 

 oxidation of other minerals; the former is monoclinic, the latter 

 orthorhombic. 



Bismite, Bi 2 O 3 , is orthorhombic in artificial crystals, in nature it 

 is not crystalline. It occurs at Schneeberg, Bohemia, as a white 

 to yellowish powder. 



ILMENITE 



Ilmenite. Menaccanite ; Titanic iron ore ; Ferrous metatitan- 

 ate, FeTi0 3 ; FeO = 47.3, TiO 2 = 52.7 ; Hexagonal ; Type, 

 Hexagonal Alternating, c = 1.3845 ; 1011 A 1101 = 94 29' ; 0001 A 

 1014 = 21 47'; 0001 A OU2 = 38 38' ; 0001 A 2243 = 61 33'; 

 Usual_ forms, _c (0001), a (1120), m (lOlO), _r (lOll), e (0112), 

 u (10T4), n (2243) ; Twinning plane, 0001 or lOTl, usually lamellar ; 

 Cleavage, none ; Brittle, fracture conchoidal ; H. = 5-6 ; G. = 

 4.5-5 ; Color, black to brownish ; Streak, black to brownish ; 

 Submetallic ; Opaque ; At times slightly magnetic. 



B.B. Fuses on the thin edges in a strong R. F., and becomes 

 magnetic; otherwise infusible. Well powdered and fused with 

 soda, the fusion boiled in strong HC1 and reduced with powdered 

 tin, yields a violet colored solution (titanium). Reacts for iron 

 with the fluxes. 



General Description. Crystals are tabular parallel to the base, 

 usually combinations of the prism a, the rhombohedron r, and the 

 base or combinations of the base and the rhombohedrons r, s, and n. 

 When tabular the base is often marked with striations, forming 

 triangular areas in outline, as the striations are parallel to the 

 rhombohedral faces. The tabular crystals are often grouped in 

 rosette aggregates, or " eisenrosen " as is hematite. Bright and 

 well-formed crystals are not common. It is usually massive, com- 

 pact, or in disseminated, rounded grains, or as sand. 



