182 DESCRIPTIONS OF MINERALS. 
usually contain much phosphorus, from organic sources, 
and hence the iron afforded is best fitted for castings. Li- 
monite 1s also pulverized and used for polishing metallic 
buttons and other articles. As yellow ochre, it is a common 
material for paint. 
_ Gothite (Pyrrhosiderite, Lepidokrokite) is another iron hydrate, often 
in prismatic crystals, as well as fibrous and massive, of the formula Fe 
O,H,(=Fe 0, +H, 0), and @. =4-0-4:4, 
Turgite has the formula KeO;H,=2Fe0,+H,0. Xanthosiderite 
and limnite are other related hydrates. 
Melanterite.—Copperas. Iron Vitriol. Green Vitriol. 
Monoclinic. In acute oblique rhombic prisms. JA J= 
82° 21°; OA 1=80° 37’. Cleavage parallel to O perfect. 
Generally pulverulent or massive. | 
Color greenish to white. Lustre vitreous. Subtranspa- 
rent to transiucent. ‘Taste astringent, sweetish, and metal- 
he eBrittle, = 5255 (Ge les3: 
Composition. HeO,S+7aq=Sulphur trioxide 28°8, iron 
protoxide 25°9, water 45°3=100. B.B. becomes magnetic. 
Yields glass with borax. On exposure, becomes covered 
with a yellowish powder, which results from oxidation. 
Obs. This species is the result of the decomposition of 
pyrite and pyrrhotite, which readily afford it if moistened 
while exposed to the atmosphere, and it is obtained from 
these sulphides for the arts (p. 173). An old mine near 
Goslar, in the Hartz, is a noted locality. . 
Copperas is much used by dyers and tanners, on account 
of its giving a black color with tannic acid, an ingredient in 
nutgalls and many kinds of bark. It-for the same reason 
forms the basis of ordinary izk, which is essentially an in- 
fusion of nutgalls and copperas. It is also employed in the 
manufacture of Prussian blue. With potassium ferrocya- 
nide, any soluble salt of iron sesquioxide, even in minute 
quantity, gives a fine blue color to the solution (due to the 
formation of Prussian blue), and this is a delicate test of the 
presence of iron. 
Coquimbite, Copiapite, Voltaite, Raimondite, Botryogen, Fibroferrite, 
‘Ihicite, are names of other hydrous iron sulphates ; and Halotrichite 
is an iron-alum. 
Jarosite is a hydrous iron-potash sulphate. 
Pisanite is an iron-copper vitriol. 
Lagonite. A hydrous iron borate, from the Tuscan lagoons. 

