Kyanite, Sillimanite, and Andalusite Deposits of the Southeastern ...

at some places in the Piedmont of Virginia, North
Carolina, and Georgia.
Muscovite, quartz, and kyanite are the dominant
minerals in kyanite schist; biotite, garnet, and
graphite are commonly present too, and staurolite
and tourmaline are found in some areas. Sodic
oligoclase is an abundant mineral in the garnetiferous
kyanite gneiss of the Burnsville-Swannanoa
area, North Carolina (fig. 20). The kyanite
GEOLOGY OF THE DEPOSITS 17
FIGURE 21. Photomicrograph of sillimanite-biotite-muscovite schist from
Cages Mountain, Caldwell County, N.C. Shows biotite (b) and muscovite
(m) intergrown with fine fibrous Sillimanite (s) ; in some areas biotite and
Sillimanite are very intimately mixed (b-s). Holes in section (h). Planepolarized
light.
FIGURE 20. Photomicrograph of kyanite-bearing gneiss from Yancey Cyanite
Co. mine, Celo Mountain, Yancey County, N.C. Shows kyanite (k), garnet
(g), biotite (b), muscovite (m), quartz (q), and plagioclase (pi). Black
areas of opaque mineral (o) are magnetite and pyrrhotite. Holes in section
( h). Plane-polarized light.
crystals are commonly blue. They have a wide range
in size at different localities, from about an eighth
of an inch to several inches in length. Layers of
schist or gneiss in which kyanite is rather evenly
distributed commonly alternate with layers that
contain little or no kyanite. Some quartz veins or
pegmatites carry kyanite. The kyanite content of
zones that are 100 feet or so thick ranges from a
few percent to about 10 percent; individual layers
contain 15 percent or more of kyanite.
SIKLIMANITE SCHIST AND GNEISS
Sillimanite schist has recently been found widespread
in the region, particularly in a belt in the
western Piedmont that extends from North Carolina
to eastern Georgia and in another belt in the Blue
Ridge of western North Carolina and northern
Georgia.
Sillimanite typically occurs in quartz-mica schist,
in which biotite is generally much more abundant
than muscovite; feldspar is absent from much of
the rock, though orthoclase is found in places. Other
minerals commonly present are garnet, staurolite,
chlorite, magnetite(?), pyrite, ilmenite, and tourmaline.
A little kyanite accompanies the Sillimanite
at some localities. Sillimanite occurs most commonly
as clusters of fine fibrous crystals closely
intergrown with mica (fig. 21); it also forms coarse
prismatic crystals in some deposits (fig. 22). Sillimanite
may be concentrated in certain layers distributed
rather uniformly through the rock. Sil-
FIGURE 22. Photomicrograph of sillimanite-biotite-quartz schist from Gideon
property, about 1^ miles southwest of Cross Anchor, Spartanburg County,
S.C. Shows prismatic crystals of sillimanite (s), biotite (b), quartz (q),
and a little muscovite (m). Some sillimanite crystals are cut nearly normal
to the c axis (showing rectangular cross sections with diagonal cleavage),
and other crystals are cut nearly parallel to the c axis. Plane-polarized light.