Mullite or porcelainite's a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge balancing cations present therefore there're three different Al sites: two distorted tetrahedral Al sites and one Al other site which adopts a higher co-ordinate octahedral state. Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. It's produced artificially during various melting and firing pro… (More on Mullite)