The veins attain a maximum width of 60 feet in Arkansas and nearly 100 feet in Oklahoma. They are most numerous along the central core of the Ouachita Mountain region, where they are present in shale, slate, sandstone, and other rock types. Along and near the borders of this region, the veins are usually confined to sandstone beds encased within thick shale units. The more than 25,000 feet of Paleozoic rocks exposed in the Ouachita Mountains have been deformed into complex, gently plunging folds that trend nearly east-west. Steeply dipping fractures closely related to the major folds and faults of the region controlled the location and deposition of most of the quartz.
Geologic environments See the state geology map .
The mineral quartz forms in a variety of geologic environments. Because quartz forms under so many conditions and is resistant to most of the forces of weathering, it is the second most common mineral in the earth's crust, feldspar being the most common. Let's discuss each one of these types of formation in some detail. Quartz that forms from the crystallization of magmatic rocks crystallizes from a melt that is rich in silica and water. The crystals usually do not express their own crystal form, but instead fill voids between other earlier-formed minerals.