400 DESCRIPTIVE MINERALOGY. 



localities. Those pyrites which are subject to decomposition usually afford specimens of the 

 sulphate of iron, either in its pure form, or mixed with alumina. Prof. Shepard remarks, 

 that numerous localities of copperas have been found in New-England, " in wliich it exists in 

 the form of crusts upon the surfaces of those mica slate rocks, which happen to abound in 

 iron pyrites."* 



ALUMINA-SULPHATE OF IRON. 



This mineral, described by Dr. Thomson, is said to have been found abundantly in the shale of the wrought out coal 

 beds at Hurlet and Campsie, near Glasgow. 



DESCRIPTIO^. Colour snow-white. It occurs in fine needles about an inch long, having 

 some breadth, but no sensible thickness. Taste sweet and astringent. Soluble in water. 

 When heated, it loses water and becomes red. 



Composition. Sulphuric acid 35.60, protoxide of iron 13.56, alumina 7.13, water 43.71 

 (Thomson). Sulphuric acid 28.64, protoxide of iron 19.93, alumina 2.85, water 48.58 

 ( Thomson). 



From the above analyses, and those of Berthier and Phillips, it appears that the mineral 

 varies considerably in its composition. 



A mineral resembling the one here described, is found associated with the lignite, clay and 

 iron pyrites at Rossville in Richmond county. 



CHROME-IRON ORE. 



Fer Chromate. Haiiy. — Chromate of Iron. Clmveland and Phillips. — Chrome-iron Ore. Thomson. — Chrome 

 Ore. Shepard. — Octahedral Chrome Ore. Jameson. — Octaedrisches Chrom-Erz. Molis. — Eiscnchrome. 

 Beudant. 



Fig. 475. Description. Colour iron-black or brownish black. Streak brown. 



It occurs regularly crystallized ; also massive and disseminated in 

 grains. Primary form tlie regular octahedron. Fig. 475. Cleavage 

 parallel with the primary, but imperfect. Fracture uneven. Lustre 

 imperfectly metallic. Opaque. Hardness 5.5. Specific gravity 

 from 4.32 to 4.50. Occasionally magnetic. Infusible by the blow- 

 pipe alone ; with borax, it melts slowly, and on cooling, exliibits the 

 fine green colour of the oxide of chrome. It is insoluble in nitric 

 acid. 



Composition. Specimen from Bare hills near Baltimore — Green oxide of chrome 52.95, 

 peroxide of iron 29.24, alumina 12.22, white matter 3.09, water 0.70 [Thojnson). Formula 

 FeO + CrA- 



* Treatise on Mineralogy. 



