McCollum Quarry, Newman, Coweta County, Georgia, USAi

Regional Level Types
McCollum Quarry	Quarry
Newman	- not defined -
Coweta County	County
Georgia	State
USA	Country

On the property of Mr. J. R. McCollum, of Newnan, Georgia, occur several outcrops of a coarse-grain porphyritic granite, nine miles northeast from Newnan, on the Atlanta and West Point railroad, near Coweta station. Approximately one acre of the exposed granite occurs three eighths of a mile slightly north of east from the station, on a gently sloping hill. Outcrops are seen along several small streams, from two to two and a half miles south of east from the above field-exposure, the principal one of which includes one and a half acres, located about one hundred yards from the east fork of Shoal creek, and two miles east from Coweta station. A good section of the partially fresh and decayed rock is shown in a cut of the Atlanta and West Point railroad, a short distance north of the station. The exposures on Mr. McCollum's place indicate a belt approximately three miles long, in a northwest-southeast course, and as much as three quarters to one mile wide, in places. Several handsome blocks of the stone have been collected for exhibition purposes. One of these is on exhibition in the State Museum at the Capitol in Atlanta. The excellent finish, the rock is capable of receiving, is well shown in the polished and hammer-dressed faces of the eight-inch cube in the State Museum.

Megascopically, the rock is a very coarse-grain porphyritic biotite granite, of medium-gray color. The porphyritic minerals are the potash feldspars, orthoclase and microcline.

The phenocrysts measure two inches and more in length, in extreme cases; and are prevailingly irregular in outline; but they are frequently tabular, parallel to the clinopinacoid (010), and twinned according to the Carlsbad law. Cleavages parallel to the base (001) and clinopinacoid (010) are generally well developed.

Microscopically, the rock is very coarse-grain, and porphyritic in texture, and is composed of quartz and the potash feldspars, and plagioclase with biotite. The quartz anhedra are crossed by lines of fracture, and, in addition, display wavy extinction. The plagioclase is lath-shaped in outline, and exhibits broad twinning-bars with small extinction angles, in basal sections, indicating a feldspar near oligoclase. The orthoclase shows good cleavage and is intergrown with both plagioclase, probably albite, and quartz in the form of microperthitic and micropegmatitic inter-growths. Biotite is present in large grouped plates, with deep color, strong absorption, good basal cleavage, and containing numerous inclusions. Some epidote, chlorite and muscovite occur as secondary minerals. The feldspars contain an unusually large proportion of fairly large prismatic inclusions of apatite.