porcelainized

Baked like potters’ clay; specifically, in geology, hardened and altered, by contact or other metamorphism, so as to resemble in texture porcelain or earthenware: said of clays, shales, and other stratified rock. Also spelled porcelainised.

Baked like potter’s lay; — applied to clay shales that have been converted by heat into a substance resembling porcelain.

Simple past tense and past participle of porcelainize.