Basic Guidelines For English Spellings
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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.
Late 18th century; earliest use found in Richard Kirwan (1733–1812), chemist and mineralogist. From German Porzellanit (attributed to J. T. A. Peithner by Kirwan) from Porzellan + -it.