Refractory clay is not a single mineral, but a mixture of various hydrous aluminosilicate minerals with a diameter of less than 0.001mm (or less than 1~2μm).

Refractory clay is plastic in wet state and fine powder state (obtained by mixing after crushing and adding water), hardens after drying and vitrifies when heated at a high enough temperature.

Clay can be divided into:

native clay. Refers to the weathering of feldspar to produce kaolinite and other hydrous silicate minerals, quartz, etc. Particles that are not fully weathered remain in place, while soluble salts are dissolved.

secondary clay. It is the clay that is transferred to other places and re-deposited by the original clay under natural dynamic conditions.

The chemical composition, impurities and companions of primary clay are restricted by the composition of parent rock.