Clay Minerals in a Limestone Soil Profile

Abstract

AbstractThe clay minerals in a soil developed from Lenoir limestone (Ordovician) in Augusta County, Va., are kaolinite and chlorite. The Lenoir limestone contains clay partings consisting of hydrous mica, and the clay in the soil is considered to be residual from that in the parent limestone and modified by soil-forming processes (podzolic). X-ray diffraction patterns of the clay fraction (<2μ) from samples from different positions in the profile show a reduction in hydrous mica and an increase in kaolinite and chlorite content as the A horizon is reached. Partial chemical analyses of the whole soil and of the clay fractions are given, as well as pH and ion-exchange capacity determinations. The silica-alumina ratios are similar to those characteristic of podzolic soils, and excess silica in the A horizon accumulates as recrystallized quartz together with chert which is considered to be residual from the limestone. Mechanical analyses by the standard pipette method show that the quantity of clay in the soil varies from 17 percent at the surface to 61 percent at 26 inches (C horizon).