瓷土

[ noun ]
a fine usually white clay formed by the weathering of aluminous minerals (as feldspar); used in ceramics and as an absorbent and as a filler (e.g., in paper)
<noun.substance>

Kaolin \Ka"o*lin\, Kaoline \Ka"o*line\, n. [Chin. kao-ling.]
(Min.)
A very pure white clay, ordinarily in the form of an
impalpable powder, and used to form the paste of porcelain;
China clay; porcelain clay. It is chiefly derived from the
decomposition of common feldspar.

Note: The name is now applied to all porcelain clays which
endure the fire without discoloration.