Mullite or porcelainite is 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. As a result, there are three different Al sites: two distorted tetrahedral sites and one octahedral.