38 CORUNDUM IN THE UNITED STATES. [bull. 180. 
is twice that of the emery and there is a large demand for a well- 
cleaned commercial product. There are a number of reasons for this 
condition : the better deposits have been so controlled and tied up 
that they could not be worked, an imperfectly cleaned product has 
been put on the market, and other minerals have been substituted for 
this one. 
It is still too soon to predict to what extent recent discoveries 
of corundum in Canada and India will add to its production. Some 
of the Canadian depOvSits in Ontario were granted by the government 
to the Canada Corundum Company, Limited, of Toronto, and this 
company began extensive operations on the deposits at the beginning 
of 1900. This corundum, which occurs in a syenite similar to that 
described on page 30, has been thoroughly tested and has given fairly 
satisfactory results. The reports of the bureau of mines at Toronto 
show that this ore carries 14.7 per cent of corundum and that a very 
clean product is obtained. If the ore from this extensive Canadian 
bed continues to carry so large a percentage of the mineral, can be 
readily cleaned, and shows good abrasive qualities, this deposit should 
play an important part in the world's production of corundum (see 
page 88). 
The India corundum occurs at Pipra, South Rewah. It is pink in 
color, with a fiue-grained massive structure, and very tough. It is 
reported that there is an unlimited supply of this material, and it 
has already been used in this country in the manufacture of certain 
oilstones (see page 89). 
In the following descriptions of localities those that contain sap- 
phires are first taken up, then the corundum, and last the emery. 
SAPPHIRE OR CORUNDUM GEMS. 
The properties of a mineral that determine its rank as a gem are 
hardness, color, rarity, index of refraction, and luster. As an illustra- 
tion of the extent to which the hardness affects the value of a min- 
eral for gem purposes, sphalerite might be cited. This mineral, which 
has an index of refraction and a luster not far below that of the dia- 
mond, has a hardness of only 3.5 to 4, which effectually cuts it off 
from being a gem mineral. 
Corundum lias properties that place some of its varieties among 
the most valuable gems. With the exception of the diamond, it is the 
hardest mineral known, and the rarity and color of the ruby, the red 
corundum, has made that gem, when more than a carat in weight, 
more valuable than a diamond of corresponding weight. Corundum 
has been found in almost all the colors of the rainbow, and in the 
following list its gems have been classified according to color. Thej T 
are very often designated by the prefix "oriental," to distinguish them 
from gems of the same name whose mineral composition and character 
ate entirely different. 
