PHYSIOGRAPHY. 155 



Crichtonite. 



Lustre imperfectly metallic. Color dark iron-black. 

 Streak black. Opake. 



Brittle. Hardness =5-0 ... 5-5 Sp. gr. = 4-661 . 



Compound Varieties. Twin-crystals : axis of revolu- 

 ion perpendicular, face of composition parallel to a : angle 

 )f revolution = 60. (See fig. 129.) 



The compositions of tbis kind hitherto observed are not 

 juite regularly formed, but consist generally of several al- 

 ;ernating laminse. The situation of the individuals is, how- 

 ever, recognizable from the direction of their faces. 



1. The foregoing description is principally derived from the species 

 Jlxototnous Iron- Ore of MOHS, under which it is believed that the 

 Crichtonite falls; and within the present species also must be included 

 the Ilmenite of Prof. KUPFER, who describes it as occurring in various- 

 y modified oblique four-sided prisms, and as having a black color, brown- 

 ish streak, shining lustre and a conchoidal fracture ; without cleavage, 

 fragments sharp-edged and opake. Hardness = 4. Sp. gr. =4-75. 



2. Alone before the blow-pipe, it does not suffer any alteration what- 

 soever. With the fluxes it acts in general like pure oxide of iron ; 

 but when dissolved in salt of phosphorus and the glass is reduced, there 

 appears as the color of the oxide of iron vanishes, a more or less distinctly 

 red color, the depths of the color depending upon the relative quantity of 

 the titanium in the variety employed. 



3. jlnatysis. 

 Variety Ilmenite. 



Titanic acid . . . 46-67 



Oxide of iron . . . 47-08 



Oxide of manganese . . . 2-39 



Magnesia . . . 0-60 



Lime . . . 0-25 



Oxide of chrome . . . 0-38 



Silica . . . 2-80 



4. It occurs in imbedded grains and crystals, in several varieties of 

 Mica and dolomite, in the valley of Gastein in Salzburg, and frequent- 

 ly along with the crystals of Rutile, over which it often forms a black 

 coating, as at Kluttau in Bohemia, in the gold streams of Ohlapian in 



