Aenigmatite

Aenigmatite, also known as Cossyrite after Cossyra, the ancient name of Pantelleria, is a sodium, iron, titanium inosilicate mineral. The chemical formula is Na₂Fe₅TiSi₆O₂₀ and its structure consists of single tetrahedral chains with a repeat unit of four and complex side branches. It forms brown to black triclinic lamellar crystals. It has Mohs hardness of 5.5 to 6 and specific gravity of 3.74 to 3.85. Aenigmatite forms a solid-solution series with wilkinsonite, Na₂Fe₄Fe₂Si₆O₂₀.