"The
name unakite was applied by Bradley" in 1874 to a variety of granite
from the Unaka Mountains in North Carolina, composed of the essential
minerals yellow-green
epidote, pink
feldspar, and quartz. Unakite has since been noted at two localities in
Virginia— (1)
at Milams Gap, near Luray, in Page and Madison counties,
6 in the Blue Ridge of
northern
Virginia, and
(2) about 2J miles south of Troutdale, Grayson County,
" in the Blue Ridge region of
southwestern
Virginia.
The mineral
composition of the unakite from the Virginia
and North Carolina-Tennessee localities places it
among the granites, with epidote as
an essential constituent, but, according to an analysis by Phalen,
quoted below, of specimens from Milams Gap, Virginia,
the rock is relatively basic for a granite.
In the Milams Gap
locality the unakite is a moderately coarse but irregular
crystallization of red feldspar, quartz, and green epidote. Irregular
crystallization of the rock is shown in the variation from masses
composed of more than two-thirds of the red feldspar through all
gradations to masses composed of quartz and epidote
without feldspar—epidosite.d
Thin sections of the unakite from Milams Gap show epidote, orthoclase, quartz,
iron oxide, zircon, and apatite. The epidote
is
here secondary, as in the other localities, replacing pyroxene and
feldspar, both plagioclase and orthoclase. The unakite from Grayson
County, Va., shows deeper-colored feldspar and epidote than that from
Milams Gap. Analyses of the unakite and the unakite-bearing rock at
Milams Gap are given on page 78."