Looking for Stones Suppliers?
Let us help you find the right suppliers!
Free, Easy, Simple way to find Suppliers.
Corundum is the second hardest natural mineral known to science.
The History Says
One century ago, the richest corundum mine in the world was in
Canada, at Craigmont, located several kilometres south of Combermere,
Ontario, in the woodsy hill country of Raglan and Carlow Townships.
The Present Scenario
Notable Occurrences now include Burma; Sri Lanka; North Carolina and
Montana, USA; many African localities; several localities in India,
and Middle Eastern and Southeast Asian countries.
is a natural occurring oxide of alumina (AL2
with 52.9 per cent aluminium and 47.1 per cent oxygen. In hardness
(moh's scale 9) it is next only to diamond. It is valued mostly for
its abrasive property. It is also refractory, the melting point being
2010ºC and hence it is used in a sintered form in the manufacture
of special refractory crucibles, rods and other materials. Corundum is
found in rocks containing a high percentage of alkalies, deficient in
silica and excess of alumina. It is an original constituent of various
igneous rocks. It is generally found associated with rocks like
syenite. It may result from the metamorphism of high aluminous clay
and is often found associated with andalusite, kyanite and
|Highly variable. The color can be
white or colorless, blue, red, yellow, green, brown, purple, and
pink; there are also instance of color zonation.
||color intensity is variable from
different viewing directions
||vitreous to adamantine
||extreme hardness, density and
Corundum having a bright and glassy lustre, splintery and devoid of
cleavage plane and inclusions is preferred by industry for the
manufacture of superior grade abrasives. The minimum Al2O3 content in
the mineral should be 84%, though generally, a content of above 90% is
preferred. The corundum is crushed, ground and screened to grain sizes
varying from 100 to 300 mesh. The grains are utilized in the
manufacture of grinding wheels for flour and rice mills, and
workshops. Grinding wheels are manufactured either by calcining a
mixture of corundum, clay and felspar or by using sodium silicate as a
bonding agent. Finer grains are utilized for the preparation of
grinding-pastes for the automobile industry. MgO and MgCl2 are used as
bonding agents. Corundum paper and cloth finished to belts, discs,
rolls, sheets and other shapes are prepared by giving a suitable
coating generally of sodium silicate.
Due to its hardness corundum also finds use in mortars, wire drawing
dies, thread guides and gauge blocks. Gem varieties are sometimes used
for pivot supporteres in delicate scientific instruments, as jewel
bearing in watches.
Corundum in small quantities is used in the manufacture of special
sparking plugs, muffles, pyrometer tubes, rod and insulator for vacuum
tubes of all kinds and crucibles. Finely ground corundum, passing
through 200 mesh, the alumina content not below 90%, is used for teh
manufacture of the above products by giving a bond of clay. The
presence of iron and felspar in corundum for the manufacture of above
products is regarded objectionable.
Natural abrasives are being fast replaced by manufactured abrasives.
The common manufactured abrasives are silicon carbide, fused alumina,
emery and boron carbide. Silicon carbide is sold under the trade
in plating to produce a hard, beautiful surface and to prevent
is an intimate mixture of alumina and iron oxide. It is manufactured
by fusing bauxite. Emery also occurs in the natural state. It is mined
in Greece and Turkey. Boron carbide known as Norbide, is the hardest
known manufactured abrasive. In hardness, if not equal, it is very
close to diamond. Although great advancement has been made in some
countries in the production of synthetic or manufactured abrasives,
yet natural abrasives have retained their eminent place and are still
being used in bulk, because of their easy availability and
characcteristics. The reason for natural corundum being particularly
suitable for certain kinds of grinding is its prominent basal cleavage
that causes the crystal to break readily with a smooth flat surface at
right-angles to the axis of elongation through successive reductions
in size unlike synthetic corundum (alumina) which has a conchoidal
Still Searching for Suppliers?
Let us help you find the right suppliers!
and receive quotes from genuine suppliers!