Clay - A finely-grained natural rock or soil containing mainly clay minerals

"Clay is a type of fine-grained natural soil material that contains hydrous aluminium phyllosilicates that develops plasticity when wet. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. - Wikipedia"