Filipstadite
Filipstadite is a very rare mineral of the spinel group, with the formula (Mn,Mg)(Sb0.5Fe0.5)O4. It is isometric, although it was previously though to be orthorhombic. When compared to a typical spinel, both the octahedral and tetrahedral sites are split due to cation ordering. Filipstadite is chemically close to melanostibite. The mineral comes from Långban, Sweden, a manganese skarn deposit famous for many rare minerals.