is a natural oxide of alumina having a formula A12O3
hardness it is next only to diamond and is valued mostly
for its abrasive property. It is also refractory, the malting
point being 2010o C and hence it is used in a
sintered form in the manufacture of special refectory crucibles,
rods other materials. Ruby and Sapphire are the gem varieties
of corundum. These are used as pilot supports in delicate
scientific instrument and as jewel bearings in watches.
is no BIS specification for corundum to be used in any industry.
user industries prescribe the specification as under: -
abrasive purposes, the corundum should have a bright and
glassy lusture; the broken grains should be angular and
sharp and should have no cleavage or parting planes. Corundum
of fine and flour grades is used as loose grains for polishing
metals, rooks and gems and for grinding and beveling glass.
For lens grinding and polishing corundum grains of rigid
size and quality are required. Corundum grains are used
in the manufacture of grinding wheels, corundum cloth and
quantities are used for this purpose, finely ground corundum
passing through 200 mash having alumina content not below
90% is used.
corundum is used for making ceramic tiles and concrete slabs.
Corundum used for this purpose should pass through 120 mesh
with Fe content preferably below 2% while presence of feldspar
is not objectionable. For cement tiles, a coarse grade of
corundum between 20 – 40 mesh is used.
this industry alumina is limited to 70%. Future trends these
days artificially prepared abrasive like fused alumina (synthetic
corundum) and these products are sold under the trade names
as abundum, aloxite, borolum, lionite and oxaluma.
reserves have been classified in to semi-precious industries
and abrasive grades as the basis of identification made and
reported by the exploration and exploitation agencies, in
the inventories as on 01.01.1980 and as on 01.01.1985, where
no information is available about the grade, the same is classified
under "Unclassified category".
following grades for classification of reserves of corundum
bright, glassy, lustre & devoid of cleavage