porcellanite
/pɔːˈsɛlənʌɪt/(also porcelanite)
noun
Geology. Originally: a hardened clay or shale resulting from thermal metamorphism; also called porcelain jasper. Later also: any dense siliceous rock with an appearance resembling unglazed porcelain.
Origin
Late 18th century; earliest use found in Richard Kirwan (1733–1812), chemist and mineralogist. From German Porzellanit from Porzellan + -it.