File:Bulletin 426 Plate XIX A Mount Airy Granite Corporation Quarry.jpg

English: Original caption: Mount Airy Granite Corporation's Quarries, Surry County, NC.
Text from the volume describing this figure:
The North Carolina Granite Corporation's (Mount Airy) quarries, located less than 1 mile northeast of Mount Airy, were opened in 1889 and the first shipment of stone from them was made in July, 1890. The total shipment of granite from these quarries from 1800, when 135 carloads were shipped, to 1904, when 1,282 carloads were shipped, was 13,232 carloads. (See Pl. XIX, A, B.)

Quarrying is confined to a 40-acre tract of continuously exposed granite over the slope and top of a long hill, which rises about 125 feet above the valley bottom. The company holds more than 200 acres additional of ground over which granite is exposed. Quarrying has extended over practically the entire 40-acre tract, the greatest depth of working being about 30 feet. The rock is a biotite granite of very light gray, nearly white color and medium grain. The biotite is not, except in one opening, equally distributed through the granite, but is entirely absent from some parts of it, is uniformly distributed through others, and shows a marked tendency to segregation in still other parts. Quartz-feldspar areas of extreme whiteness, ranging from several inches to as many feet in diameter, in which biotite is entirely lacking or represented by only a few shreds, are common through the granite. This unequal distribution of the characterizing accessory (biotite) renders the granite in places less uniform in color than might be desirable for some purposes. The granite that has a uniform color is most pleasing in appearance and forms excellent and desirable stone for all uses except for monumental stock, for which the contrast of color between the cut and polished faces is not great enough.

Microscopically the principal minerals are potash feldspar (orthoclase and microcline), soda-lime feldspar (oligoclase) , quartz, and biotite, with accessory apatite and zircon, and secondary chlorite, epidote, light-colored mica, and iron. oxide. Plagioclase feldsparexceeds the potash feldspars in amount. Zonary structure and Carlsbad twinning are beautifully developed in some of the feldspars. Intergrowths of the feldspars with one. another and with quartz are abundant.