SPECULAR OXIDE OF IRON. 



23 



Fig. 6. 



SPECULAR OXIDE OF IRON. Cleaveland. 



Fer Oligiste. Hauy. — Rhomliohedral Iron Ore. Jameson. — Specular iron Ore. Thomson. — Specular Iron. Phillips, Dana 

 and Shepard. — Oligiste. Beiidant. — Rhomboedrisches Eisen-erz. Mohs. (It includes the true Specular Iron, Iron froth, 

 Iron Mica, Red Hematite, Red Clay Ironstone, Red Siliceous Ironstone, Red Ochre, &c.) 



Under the above name are now included many varieties which pass into each other by 

 ahnost imperceptible gradations, so that it is impossible to draw the line of specific distinction 

 between them. 



Description. Colours dark steel-grey bordering on iron-black, iron-black and brownish red. 

 The powder in all cases is some shade of red, usually cherry-red, or reddish brown. It is 

 sometimes feebly magnetic. 



Occurs regularly crj'stallized ; in granular, lamellar and fibrous distinct concretions ; massive, 



disseminated, reniform, botryoidal, stalatitic and globular. 

 The primary form is a rhombohedron. P on P' = 86° ICK, 

 P on P'' = 93o 50'. 



The mineral sometimes assumes the form of an octa- 

 hedron, sometimes of a triangular dodecahedron, with its 

 apices truncated, either very deep, or near the apex. 



Lustre from splendent to dull, and is metallic or semi- 

 metallic. Fracture conchoidal or earthy. Usually opaque, 

 but sometimes thin lamina are faintly translucent. Hard- 

 ness 5.5 to 6.5. Specific gravity 4 • 8 to 5.3 {Jameson) ; 

 of a crystallized specimen from Sweden, 5.251 [Hai- 

 dinger). 



Infusible by the blowpipe per se, but melts with borax, 

 and forms a green or yellow glass, like magnetic oxide of 

 iron. It is soluble in hot muriatic acid. 



Distinctive characters. From the magnetic oxide of iron, which it often resembles, it 

 may be distinguished by its red powder, and feeble action on the magnetic needle. 



Composition. The specular oxide of iron, when pure, is a peroxide of iron, containing in 

 100 parts, 69.34 of iron, and 30.66 of oxygen. It seldom occurs in nature in this state of 

 purity, but is generally mixed with silica, alumina, lime, &c. ; and upon the proportion of 

 these must depend the value of any particular variety of ore. In a table exhibiting llie com- 

 position of various specimens of the specular oxide, according to the analyses of Berthier 

 and others, the amount of peroxide of iron varies from 28 to 99 per cent, the latter propor- 

 tion being found only in a specimen from the department of Moselle, in France.* It may be 



* Berthier. Trnitc de$ Essais par la Vote Seche, II. 223. 



