Zoned and unzoned perthite-quartz-plagioclase-muscovite pegmatites in the form of tabular bodies, irregular bodies with tabular branches, irregular masses, elongate lenses, lit-par-lit zones, and small augen and stringers are distributed throughout the Precambrian metasedimentary rocks of the Mica Mine area, Van Horn Mountains, Texas. Zoned bodies have a core of erthite and quartz and a plagioclase-quartz-perthite-muscovite wall zone. The pegmatites contain numerous schist inclusions, and some show evidence of contamination by biotite schist and amphibolite.

A recently discovered buried hill, at least 77 feet high, is composed of strata of the Wilcox group (lower Eocene) and covered on its flanks by cross-bedded sands of the lower Carrizo and at the top by level-bedded shales and silts of the upper Carrizo formation. Peculiar small funnel-shaped pits filled with Carrizo sand extend into the underlying Wilcox ball clay at the peak of the hill. Other extensions fill shrinkage cracks of the clay.