A fine-grained natural rock or soil material that contains one or more minerals and traces of metal oxides and organic matter. When clays are wet they are malleable and can be shaped by hand; they become hard and brittle upon drying or baking. Clays play an important part in maintaining soil fertility, making cations such as NH4+, K+, and Ca+ more accessible to plants' roots.
Adapted from "clay." Wikipedia. Wikimedia Foundation. Web. 18 Jan. 2016.