China clay (chemical name aluminium hydrosilicate).
The name kaolin is derived from the Kaoling mountain in the Chinese province of Kiangsi, a famous site for china clay. Kaolin is white, but can have a reddish, yellowish, or greyish colour due to the presence of iron, etc.

Kaolin is not only used to make porcelain, but also as a filler in paper making (e.g. for thin paper printing).