Found in a crystalline form in china clays and kaolins (p. 107).
For instance, felspar is rarely found in china clays, but is a common constituent of secondary (plastic) clays.
Kaolinic or china clays which are chiefly derived from felspar and can be isolated in a relatively pure state.
Unlike the china clays, pure lateritic clays are completely decomposed by hydrochloric acid.
As the china clays (kaolins) and ball clays on very careful elutriation all yield a product of the same ultimate composition, viz.
It is a mistake to suppose that all white clays of slight plasticity are china clays or kaolins.
The china clays (p. 104) are not used alone in pottery manufacture as they lack plasticity and cohesion.
They are by no means so pure as the china clays, and unless carefully selected can only be used for common ware.