Weathering of Stone Mountain Granite

Willard H. Grant
Emory University, Atlanta, Georgia

Abstract: The weathering of Stone Mountain Granite (adamellite) forms kaolinite, endellite, allophane and gibbsite of which kaolinite is the most stable. Bulk density ranges from 2.65 in fresh rock to a minimum of 1.48 in saprolite. It is a good index of weathering. Abrasion pH ranges from 5.0 in saprolite to 9.3 in fresh rock, and is directly related to bulk density and the amount of clay mineral. Among the original minerals, biotite is least stable, followed by oligoclase. Residual microcline fragments occur at the base of the B horizon indicating that it is not completely weathered. Muscovite weathers slightly and quartz appears quite stable.

Evidence shows that solution and reconstitution is necessary in the formation of some if not all clay minerals. This is particularly evident in the formation of endellite veins.

Expansion of the rock in the early phases of weathering occurs but does not produce a significant increase in volume.

Clays and Clay Minerals; 1962 v. 11; no. 1; p. 65-73; DOI: 10.1346/CCMN.1962.0110106
© 1962, The Clay Minerals Society
Clay Minerals Society (www.clays.org)