Mellite
Mellite, also called honeystone, is an unusual mineral being also an organic chemical. It is chemically identified as an aluminium salt of mellitic acid, and specifically as aluminium benzene hexacarboxylate hydrate, with the chemical formula AlC(COO)·16HO. It is a translucent honey-coloured crystal which can be polished and faceted to form striking gemstones. It crystallizes in the tetragonal system and occurs both in good crystals and as formless masses. It is soft with a Mohs hardness of 2 to 2.5 and has a low specific gravity of 1.6. It was discovered originally in 1789 at Artern in Thuringia, Germany . It has subsequently also been found in Russia, Austria, the Czech Republic, and Hungary. It was named from the Greek "meli" "honey", in allusion to its color. It is found associated with lignite and is assumed to be formed from plant material with aluminium derived from clay. Structure. The crystal structure of mellite has been determined by neutron diffraction and consists of slightly distorted Al(HO) octahedra linked by hydrogen bonds to [C(COO)] mellitate anions and water of crystallization.