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PYRITE.
Pyrite or iron pyrites is a yellow mineral of metallic lustre
consisting of the disulphide of iron, FeS 2 . It occurs in massive
form or as crystals, usually of cubic or octahedral habit. When
pure it contains 46-6 per cent of iron and 53-4 per cent of
sulphur.
Pyrite is one of the most widely distributed minerals,
occurring in rocks of every type and age. It is also a common
vein mineral, in some cases constituting practically the entire
vein matter.
USES.
The main use of pyrite is as a source of sulphur in the manu
facturing of sulphuric acid. The mineral is roasted in an oxidiz
ing atmosphere, in specially designed furnaces. The sulphur
content burns to sulphur dioxide (SO2), and the iron to ferric
oxide (Fe 2 0 3 ). The gaseous sulphur dioxide is further treated
to convert it into the trioxide (SO3), which on taking up water
becomes sulphuric acid (H2SO4). The ferric oxide which is
the solid product of the roasting process, often spoken of as
pyrite residue or cinder, is of the same composition as hematite.
It is frequently smelted for its iron content, or, if the original
pyrite contained copper, gold or silver values, these metals may
be extracted by smelting or some other metallurgical process.
The pyrite residue is used also for making paint. It is a bril
liant red and makes the pigment known as red oxide or Indian
red. The residue from a well roasted pyrite contains about
one-half a per cent of sulphur.
In his report on pyrites, 1 Dr. Wilson states that "pyrites
suitable for acid making should contain as much sulphur as
possible The greater number of acid makers demand
a product containing not less than 42 per cent sulphur; there are,
1 “ Pyrites in Canada,” by Dr. A. W. G. Wilson, Report No. 167, Mines Branch.
This report deals in detail with the subject of pyrite, its occurrence in Canada, the
methods of exploitation, dressing, and its uses. There are chapters on sulphuric acid making
and the use of pyrite in the pulp industry.