DISTRIBUTION IN UNITED STATES. 97 
the excess of the aluniiiia crystallized out as cornndum. This mineral 
has crystallized out along the planes of lamination, so that during 
the subsequent weathering of the rock the corundum has been left in 
knotty nodules, studding the surface of the rock and giving it the 
appearance of containing a high percentage. 
This view of the conversion of rich aluminous shales or bauxite 
into corundum is strengthened by the experiments nuide in the arti- 
ficial production of corundum from bauxite, a hydrous aliuninum 
oxide, by means of very great heat and pressure in an electrical fur- 
nace, as described on page 75. 
DISTRIBUTION OF CORUI^DUM IN THE irXITED STATES. 
Although there are many localities throughout the United States 
where corundum has been found, only a few of these contain this min- 
eral in quantity, and still fewer give evidence of developing into 
commercial deposits. Most of the corundum that has been mined in 
the United States for abrasive purposes has been obtained from the 
Eastern States, principally from Massachusetts and New York, which 
furnish the emery variety, and from Georgia and North Carolina, 
which furnish corundum. During the last two years the corundum 
deposits of Montana have been developed, and their product has been 
put on the market. The sapphire variety of corundum has been 
mined quite extensively in Montana, and to a more limited extent in 
North Carolina. The general location of the corundum deposits of 
the United States is indicated on the map, PI. I. With the excep- 
tion of a few localities in Montana, two in Colorado, one in Idaho, 
and one or two in California, all the known occurrences of corundum 
in the United States are confined to the Appalachian belt. 
In the following descriptions of localities, those that contain the 
^apphire variety are first taken up, then those containing corundum, 
and last, those containing emery. 
SAPPHIRE OR GEM CORUNDUM. 
RUBY. 
Sapphire or cornndum gem occurs in the mines in three forms : First, 
IS crystals, of which there are two distinct forms, ( 1 ) hexagonal prisms 
terminated by rhombohedrons and pyramids, sometimes with basal 
plane, the larger crystals being often rounded or barrel shaped, and 
(2) flat, tabular crystals, where the basal jolane is very largely devel- 
oped; second, as transparent colored portions of larger massive 
pieces of corundum; third, as nodules of finer and clearer material 
Bull. 2G9— OG M 7 
