22 
CORUNDUM IN THE UNITED STATES. 
[bit i j,. 180. 
oxide Many microscopic grains of picotite or cliromite arc scattered 
through the groundmass of the edenite. There is also present, in 
widely varying proportions, the plagioclase feldspar anorthite. The 
feldspar is not constant in all of the amphibolites, and where it does 
occur it varies in size from minute particles to masses as large as a pea. 
The rock has often a very strikingly laminated structure, and grades 
from that to one which shows no lamination at all. It is exceedingly 
tough and very fine grained. The corundum, which occurs in the 
amphibolite as an accessory mineral, varies in size from minute parti- 
cles to masses several inches in diameter, in which there are usually 
developed parting planes parallel to the unit rhombohedron. In color 
it varies from almost white to a deep ruby red, but the prevailing color 
is a deep pink. 
SHAFTS sWD curs 
CONTOUR INTERVAL 50 FEET 
Fl« 
-Map of the Buck Creek peiidotite area, showing the relation of the amphibolite dikes. 
On account of the exceeding toughness of the rock, and more par- 
ticularly on account of the low percentage of corundum, these amphib- 
olites are not of commercial value as a source of corundum; they 
do, however, make handsome mineral specimens. 
On the eastern slope of the Blue Ridge, in the vicinity of States- 
ville, Iredell County, N. C, corundum has been found associated 
with an amphibolite composed of a dark-green hornblende. On 
account of the thickness of the soil and the depth to which these 
rocks have been decomposed, there are few places where the fresh 
rocks are exposed, and little is known of their extent. At Hunters, 
7 miles west of Statesville, the amxDhibolite was exposed during 
1 Bull. Geol. Survey North Carolina No. 11, 1896, p. 59. 
