48 CORUNDUM^ ITS OCCURRENCE AND DISTRIBUTION. 
CORUNDUM IN GRANITE, 
At Nannies Mountain, 12 miles northeast of Yorkville, S. C, 
corunchnn occurs in considerable quantities in a light-gray biotite- 
granite. It forms irregular masses of a black color, varying from 
small grains to several inches in thickness, and usually has a well- 
developed parallel parting. It is invariably embedded in muscovite, 
which varies from fine scaly aggregates to compact massive damourite. 
At the Rickard mine, at the north end of the mountain, a shaft 35 
feet deep has been sunk, and several drifts have been made from it ; 
but, as operations have been suspended, these workings can not be 
examined. Hence the exact relations of the corundum masses to the 
granite can not be made out. Only granite, however, in various 
stages of disintegration, and masses of corundum and muscovite were 
taken from these workings. 
Dr. A. Lacroix^ found corundum in masses of granite included in 
the volcanic rocks of Auvergne, France; and its occurrence as an 
occasional accessory in normal granites is mentioned in the petro- 
graphical works of both Zirkel and Rosenbusch. 
CORUNDUM IN SYENITE. 
Deposits of corundum have recently been located in the south-cen- 
tral part of Gallatin County, Mont., on the headwaters of Elk Creek, 
in a group of foothills between the Gallatin Valley and Spanish Creek 
basin. The locality is about 23 miles south of Belgrade, Gallatin 
County, which is on the Northern Pacific Railroad. The corundum 
has been found in a rock that is composed essentially of orthoclase, 
feldspar, corundum, and biotite, with the feldspar predominating. 
The rock for the most part has a somewhat gneissoid structure, and 
in these portions the corundum is more or less finely divided, being 
in fine grains and small crystals. In other portions, where the corun- 
dum is coarsely crystallized, the rock has something of a pegmatitic 
character, and the corundum is surrounded by the orthoclase. This 
rock is called a corundum-bearing biotite syenite, yet from the num- 
ber of occurrences that are recorded of this mineral acting as a com- 
ponent of these rocks, as in the case of those in Canada and in the 
Urals, it would seem desirable to recognize rocks of this type as 
corundum-syenites. 
The crystals of corundum vary from a fraction of an inch up to 8 
inches in length, and some have been found that weighed 1| to 2 
pounds each. They are fairly well developed in the prismatic zone, 
but many of them, especially the larger ones, are rounded. In color 
they vary from bluish gray to almost colorless. 
^BuJl. Services Carte geol. France, No. 11, vol. 2, 1891. 
