Re: Clay soil

Message ID: 858871350.Es

VAL:

The most likely source for the clay in your region's soils is from chemical weathering of the mineral feldspar.

Feldspar is a common mineral in many igneous rocks and therefore occurs in many metamorphic rocks as well. It also occurs in a few types of sedimentary rocks, but is far from common.

Chemical weathering is the decay, dissolution, or decomposition of minerals by a variety of chemical processes, most of which involve water.

When feldspar weathers (as it is doing at the surface where you live) under the influence of chemical attack, it undergoes a process known as hydrolysis. Hydrolysis involves the addition of water to the molecules within feldspar's internal structure. Hydrolysis helps convert feldspar into clay minerals.

So, the source for the clay is probably the chemical weathering of feldspar. The source for the feldspar is probably the igneous (and/or metamorphic) rocks of the Berkshires (or perhaps glacial drift; see below). The most common igneous rock in the Earth's upper continental crust, granite, contains abundant feldspar; as does gneiss, a common metamorphic rock in the continental crust. Both of these rocks are found in many mountainous regions.

The stones and boulders in your soil may come from two sources: glacial drift or local erosion. The Berkshires were glaciated during the most recent "Ice age." Many of the rocks in your soil may have been transported from other areas by glacial ice and deposited around the Berkshires by this ice or by meltwater from the ice. Such deposits are called glacial drift. Or the stones and boulders may simply have been transported from surrounding mountains by glacial ice, running water (streams) or gravity (mass wasting). It is also possible that both local and regional sources contributed rocks to your soil.

Whatever the source, the stones and rocks have not yet completely decomposed and/or disintegrated due to weathering, and so you find them in the soil.

Clay Harris

cdharris@frank.mtsu.edu