Geology and Mineralogy of Quartz Crystals MOST OF THE QUARTZ
veins are restricted to a belt about 30 to 40 miles wide that
extends a distance of about 170 miles west southwest from Little
Rock, Arkansas, to eastern Oklahoma. This area corresponds to
the core region of the Ouachita Mountains. The most productive
quartz veins are present in both Paleozoic sandstones and
shales, but those having shale as the host rock typically are
massive milky vein deposits with a smaller proportion of clear,
well-developed crystals. Deposits in sandstone units may be in
the form of veins, sheeted zones, and stock works. Sandstone-
hosted deposits usually contain less quartz volumetrically than
shale-hosted deposits, but often yield a higher percentage of
clear crystals in cavities or pockets. Many crystal-bearing
pockets were distorted or crushed by structural adjustments
during the Ouachita orogeny (mountain-building episode) after
initial quartz deposition. The deformation commonly causes the
veins to show complex fabrics. Q