162 CORUNDUM^ ITS OCCURRENCE AND DISTRIBUTION. 
There are now a niunber of companies that have installed complete 
concentrating mills, similar to those used in concentrating gold ores, 
but modified to suit corundum ore. While all are using jigs for the 
coarser sizes of the crushed ore, some are using Frue vanners and 
others Bartlett or Wilfley tables for the finer sizes. This method 
Avorks very satisfactorily for concentrating the corundum, and if 
during the crushing and rolling of the ore the corundum is largely 
separated from the associated minerals a nearly cleaned product is 
obtained. Methods of separation similar- to that last mentioned are 
being employed by the Canada Corundum Company on the ores 
from the Craig mine and by the Montana Corundum Company on 
the Gallatin Count}^ ores. Where, however, there are foreign min- 
erals, especially mica, attached to the particles of corundum, it is 
necessary to adopt some process similar to that performed by the 
mullers in order to eliminate the foreign minerals. 
Many other minerals that will be likely to remain with the corun- 
dum in the concentrates — as garnet, pyrite, etc. — can undoubtedly be 
separated by means of the Wetherill magnetic concentrator. Unless 
these minerals are unattached to the particles of corundum there will 
be a considerable loss of corundum by this method of separation. 
USES OF CORUNDUM. 
WATCH JEWELS. 
Corundum is used for two general purposes, as gems and as an 
abrasive. 
The varieties of corundum that are of value as gems haA^e been 
described on page 22, and the many uses that are made of the cut 
stones in the jewelry trade are too Avell knoAvn to need more than a 
passing notice here. One use of the gem corundum that is perhaps 
worthy of notice is in supplying jeAvels for Avatches. 
In a recent report by Mr. George F. Kunz," it is stated that there 
are from 10,000,000 to 20,000,000 Avatch jewels sold annually. For 
this purpose corundum gems of all colors are used. Some of these 
are sapphires and rubies Avhich are fine enough in quality to make 
gems, but of Avhich only minute pieces are used. There are also used 
those corundum gems which are of such color as to have little or no 
value as jeAvels, such as A^'ery pale sapphires and the pink, greenish, 
and yelloAv corundums. 
Many of the sapphires from Yogo Gulch, Fergus County, Mont., 
and the many colored corundum crystals from Granite County, Mont., 
which haA^e but little value for cutting into jewels, are used for this 
"Mineral Resources U. S. for 1903, U, S. Geol. Survey, 1904, p. 974. 
