528 AUSTIN F. ROGERS 



decide that melanochalcite is a mechanical mixture of tenorite, 

 malachite, and chrysocolla. While the two latter minerals may 

 sometimes be associated with it, homogeneous melaconite free from 

 mechanical impurities also gives tests for the carbonate radical and 

 silica. Melaconite is either an adsorption compound or a solid 

 solution of cupric oxid and water with silica, carbonate radical, 

 and often manganese dioxid. 



Hematite. Fe-OjQHaO);,; (hydrohematite, turgite, hematogelite) . 

 — Two varieties of ferric oxid are generally recognized, a crystalline 

 one and a massive or earthy-red one. Haiiy and Werner respec- 

 tively considered these as distinct minerals under the names fer 

 oligiste, fer oxyde rouge and eisenglanz, rotheisenstein. They were 

 united by Hausmann, and he has been generally followed by other 

 mineralogists. The red, earthy varieties of ferric oxid, such as the 

 oolitic Clinton ore and the soft hematites from the Mesabi range, 

 are amorphous and should be separated from the crystalline ferric 

 oxid. The amorphous ferric oxid may be distinguished from the 

 crystalline mineral by the fact that it contains a small amount of 

 water. 



Turgite is usually considered to be 2Fe 2 3 *H i O, but it is prob- 

 ably not a definite hydrate. Turgite often occurs in colloform 

 crusts. It sometimes shows a fibrous structure, but this is prob- 

 ably because it is a dehydration product of limonite and retains its 

 structure. In fragments turgite is very dark red, sometimes iso- 

 tropic and sometimes birefringent. The double refraction may be 

 due to strain. Turgite is essentially identical with amorphous 

 hematite. 



Specularite, now used as a varietal name by many mining 

 geologists, may be used as a specific name for crystalline ferric 

 oxid, and hematite then may be used exclusively for amorphous 

 ferric oxid. 



Limonite. Fe 4 H60 9 (H 2 0)- e ( ?) (stilpnosiderite, melanosiderite, 

 limnite, esmeraldaite, xanthosiderite ?). — Leaving gothite out of 

 consideration, hydrous ferric oxid with a yellow-brown streak 

 occurs in two distinct forms, a crystalline fibrous form and an 

 amorphous massive form. Under the microscope the former ap- 

 pears as crystalline fibers with parallel extinction, and the latter is 



