Geology Reference
In-Depth Information
B.2.14 Chlorine
Chlorine is the most common element of the halogens. In pure form, it is a green-
yellow diatomic gas. In nature meanwhile, it is found in the form of halite NaCl,
carnallite KCl and sylvite KMgCl
3
6(H
2
O). Nevertheless, it is so abundant in
the ocean, that it is here and in underground brine deposits where it is extracted
for commercial uses.
Chlorine is very reactive and combines with nearly all other elements. It is
used in water purification, disinfectants, in bleach and in mustard gas. Chlorine is
also used extensively in the manufacture of many products directly or indirectly,
i.e. in paper product production, antiseptics, food, insecticides, paints, petroleum
products, plastics, medicines and so on.
B.2.15 Chromium
Chromium is a hard transition metal. Its only ore of any commercial importance is
chromite FeCr
2
O
4
. Other less plentiful sources are crocoite PbCrO
4
and chrome
ochre Cr
2
O
3
, while the gemstones emerald and ruby owe their colours to traces of
chromium.
In iron, steel and nonferrous alloys chromium imparts hardness and resistance to
both corrosion and oxidation. The use of chromium to produce stainless steel and
non-ferrous alloys are two of its more important applications. It finds application as
a dye and/or paint in the production of synthetic rubies, as a catalyst in the dyeing
and tanning of leather. It is also used to make moulds for the firing of bricks.
B.2.16 Cobalt
Cobalt is a hard ferromagnetic, silver-white transition metal. More than 200 ores
are known to contain cobalt but only a few are of commercial value. The more
important are the arsenides and sulphides such as smaltite, CoAs
2
, cobaltite CoAsS
and linnaeite Co
3
S
4
.These are invariably associated with nickel and also with copper
and lead. Subsequently, Co is usually obtained as a byproduct or coproduct of these
metals.
The largest use of cobalt is in the superalloys, which are used to make parts
of gas turbine aircraft engines. Cobalt is also used in corrosion resistant alloys,
high-speed steels, cemented carbides, in magnets and magnetic recording media, as
catalysts for the petroleum and chemical industries and as a drying agent for paints
and inks.
B.2.17 Copper
Copper is found mainly in its sulphide, oxide or carbonate forms. Its major ores
being copper pyrite (chalcopyrite) CuFeS
2
, which is estimated to account for about
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