Clay

Clay is a type of fine-grained natural soil material. Clays get plastic when wet, but become hard, brittle and non–plastic upon drying or firing. Because of impurities, natural clays usually show various colors.
According to the nature and use, clay can be divided into ceramic clay, refractory clay, brick clay and cement clay. Hard refractory clay is usually used to make refractory materials. While in the ceramic industry, hard clay and semi-hard clay can be used as raw materials for making pottery, daily ceramics, architectural porcelain and industrial porcelain.
Nowadays, clay is also applied in many modern industrial processes, such as paper making, cement production and chemical filtering.