What is "mullite"

n. (context mineralogy English) An orthorhombic-dipyramidal mineral containing aluminum, oxygen, and silicon.

Mullite or porcelainite is a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms 3 Al O2 SiO or 2AlO SiO. Unusually, mullite has no charge balancing cations present. As a result, there are three different aluminium sites: two distorted tetrahedral and one octahedral.

Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Argyllshire, Scotland.