344 



MINERALOGY 



interpenetrating and polysynthetic ; Cleavage, none, parting caused 

 by twinning; Brittle, fracture uneven; H. = 5.5-6.5; G. = 

 4.9-5.3, varies with the structure ; Luster, metallic, splendent in 

 crystals, dull in massive form ; Color, dark iron-gray, red, reddish 

 brown, to black; Streak, cherry-red; Opaque except in thin 

 scales when blood-red by transmitted light; = 2.94; co = 3.22; 

 o>- =0.28; Optically (-). 



B.B. Nearly infusible (1350). In R. F. on coal blackens and 

 becomes magnetic, with the fluxes shows iron. Soluble in HC1 



at least in fine powder on heat- 

 ing, when impure there will be 

 a considerable residue of quartz. 



General Description. When 

 crystalline, usually in tabular 

 crystals with a splendent luster 

 or iridescent, combinations of m, 

 r, e, n, and c, with striations on 

 the base; a large number of 

 other forms have been de- 

 scribed. Micaceous hematite is 

 formed by thin scales in parallel 

 position. All highly lustrous crystalline hematites are known as 

 specular iron ore. Another peculiar complex aggregate in which 

 the individual crystals are arranged radially around the center like 

 the petals of a rose, " eisenrosen," occurs at St. Gothard, Fig. 416. 



Amorphous hematite occurs mas- 

 sive, fibrous, radiated, botryoidal, 

 concretionary, or apparently soft 

 and unctuous, " clay iron-stone," 

 which soils the fingers ; all such 

 varieties are red, brown, or even 

 slightly yellowish in color, as they 

 grade into limonite; but all true 

 hematites yield a cherry-red streak. 

 Hematite is connected with 

 igneous rocks in which it occurs as 

 a primary constituent, as black 

 scales, easily mistaken for magnet- 

 ite. Many feldspar phenocrysts, especially orthoclase, which 

 seems to have a predisposition to collect these fine hematite scales 



FIG. 



415. Hematite 

 Elba. 



Crystals from 



FIG. 416. Eisenrosen. St. Gothard, 

 Switzerland. 



