34 
CORUNDUM AND EMERY. 
Corundum, which is practically pure alumina, is, next to 
diamond, the hardest mineral found. It has a hardness of 9 
on Mohs’ scale. 
It occurs in a rock matrix from which it must be separated 
by crushing and concentration, after which it is ground and 
sized according to the demands of the markets, great care being 
taken to obtain uniform grading as regards the size of the grains. 
Owing to its hardness and to the fact that it is not brittle 
it is admirably suited for use as an abrasive. It is employed 
for grinding and polishing both in the form of powder and 
wheels. 
In the making of wheels the grains of corundum are mixed 
with clay and fluxes and moulded into shape, after which the 
wheels are “fired” at such a temperature as to establish a strong 
bond between the particles. 
Emery is an impure corundum. It is almost black in colour 
and contains magnetite and hematite intimately mixed. 1 
Its uses are the same as pure corundum but its abrasive 
power is very much less. 
The prices as reported by Canadian users vary from 5| to 
12 cents per pound for corundum, and from 2| to 7 cents per 
pound for emery, the prices depending largely upon the quan 
tities purchased. 
Amount of corundum used in the manufacturing industries, 
as reported by the consumers:— 
Location 
No. of firms 
reporting 
consumption 
Domestic 
Imported 
Tons 
Tons 
Maritime Provinces 
1 
A 
Quebec 
2 
1A 
— 
Ontario 
17 
3 
Prairie Provinces 
2 
A 
— 
British Columbia 
— 
— 
Canada (Total) 
22 
143A 
3 
1 J. D. Dana, “ System of Mineralogy.”