English: Original caption: Leopardite (quartz porphyry), near Charlotte, Mecklenburg County, NC. Section across black streaks.
Text in the volume regarding this figure:
At Belmont Springs, 1 1/2 miles east of Charlotte, a dike of quartz porphyry, whose width nowhere exceeds 25 feet and which has been appropriately named leopardite, intersects the biotite granite. It is a dense, hard, tough, and compact cryptocrystalline rock, which breaks with a conchoidal fracture. It is nearly white, tinged a faint greenish in places, and is penetrated by long parallel streaks or pencils of black color. (See PI. XV.) When broken at right angles to the streaks the surface is dotted with rounded irregular black spots, varying in diameter from that of a pin head up to half an inch. These pencils are entirely absent from some portions of the rock and are closely crowded together in others. The rock is composed essentially of a crystalline aggregate of feldspar (potash and soda-lime varieties) and quartz, with less colorless mica. Idiomorphic phenocrysts of quartz and feldspar of small size are distributed through the groundmass. The black streaks or pencils are composed of the oxides of manganese and iron. The rock is susceptible of an excellent polish and could be used with splendid effect in inlaid work.