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 which 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. 
Description. 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. 
Per Chromate. Haiiy. — Chromate of Iron. Cleaveland and Phillips. — Chrome-iron Ore. Thomson. — Chrome 
Ore. Shepard. — Octahedral Chrome Ore. Jameson. — Octaedrisches Chrom-Erz. Mohs. — Eisenchrome. 
Beudant. 
Fig. 475. 
Description. Colour iron-black or brownish black. Streak brown. 
It occurs regularly crystallized; also massive and disseminated in 
grains. Primary form the 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, exhibits 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 {Thomson). Formula 
Fe0 + Cr 2 0 3 . 
Treatise on Mineralogy. 
