40 GEMS AND PRECIOUS STONES IN THE
Corundum
is a mineral of great importance, though not of frequent occurrence; in
combination, however, especially with silica, alumina enters into a
vast number of mineral species and varieties. Its great hardness gives
it value as a polishing material, and as such it has no substitute. It
is found in the United States, chiefly in the crystalline rocks along
the Appalachian Mountains, from Chester, Mass., to northern Georgia,
and also in Montana. At Chester, where the deposits have long been
known and worked, the mineral consists chiefly of emery, which is
corundum mixed with magnetite, and somewhat softer than corundum alone.
No gems have been found here. At Pelham, Mass., corundum in small
quantities has been recognized, and Prof. Charles U. Shepard 1 found
asteriated crystals in nodules of cyanite at Litchfield, Conn., also at
Norwich, Conn., where he found small blue crystals enclosed in
fibrolite. It is likewise found in the metamorphic rocks of the
Highlands of New York and northern New Jersey. At Vernon, N. J., forty
years ago, crystals of sapphire and ruby corundum were found, but
always opaque, so that, while many specimens were obtained from this
locality, some of which have been cut, it is probable that none of them
has furnished a transparent gem.
It
is of interest to know that rubies from Mandalay, Burmah, occur in
similar association with limestone; hence they are generally found
detached and separated from their original matrix. Some handsome
cabinet specimens, showing asterism, have been obtained from Delaware,
Chester, and Lancaster Counties, Pa.; few, however, were suitable for
cutting. Crystals have been found in Virginia, in Louisa County, and
near Staunton, Augusta County.
The
great corundum region is in the crystalline rocks of North Carolina,
where in Madison, Buncombe, Haywood, Jackson, Macon, and Clay
Counties, numerous localities are known. A second and a third line of
localities are recognized, but they are of slight importance. According
to Thomas M. Chatard,2 of the United States Geological Survey, the corundum region extends from the Virginia line through the western part of
1
Report on the Geological Survey of Connecticut, p. 64, New Haven, 1837.
•Mineral Resources of the United States, p. 714, 1883-1884.
