Hydrous Oxides -  Turgite, Hydrohematite and Diaspore Composition

Composition is Fe₄O₅(OH)₂ or 2Fe₂O₃.1H₂O.  Compare limonite and goethite.  Reniform and stalactitic, with radiating fibrous structure.  Sometimes earthy.  H. = 5.5-6.  G. = 4.14.  Submetallic luster.  Color black to reddish black.  Streak Indian-red Difficultly fusible at 5-5.5. Strongly magnetic after heating in R.F. Inc C. T. gives 5 per cent of water and generally decrepitates.  Distinguished form limonite by red streak and from hematite by giving water in C.T. Found usually associated with limonite.  Occurred in considerable amount at Salisbury, Conn., where it often formed an outer layer an inch or more in thickness on the masses of limonite.

Diaspore
Composition.  A1O(OH) or A1₂O₃.H₂O = Alumina 85, water 15.

Crystallization.  Orthorhombic.  Usually in thin crystals, tabular parallel to the brachypinacoid.

Structure.  Bladed; foliated massive.

Physical Properties.  Perfect cleavage parallel to brachypinacoid. H. = 6.5-7.  G. = 3.35-3.45.  Vitreous luster except on cleavage face, where it is pearly.  Color white, gray, yellowish, greenish.

Test. infusible. Insoluble. Fine powder wholly soluble in salt of phosphorus bead (absence of silica).  Ignited with cobalt nitrate turns blue (aluminum).  Gives water in C.T. Characterized by its good cleavage, scaly structure and its hardness (6.5-7).

Occurrence.  Usually a decomposition product of corundum and found associated with that mineral in dolomite, chlorite-schist, etc. Occurs similarly in bauxite deposits.  Has been noted as an accessory mineral in metamorphic limestones.  Found in the Urals; at Schmitz, Czechoslovakia; Campolungo in Switzerland.   In the United States in Chester County, Pennsylvania; at Chester, Massachusetts; with alunite forming rock masses at Mt. Robinson, Rosita Hills, Colorado.

Name.  derived from a Greek word meaning to scatter, in allusion to its decapitation when heated.