Hausmannite

Hausmannite is a mineral form of manganese oxide with the chemical formula Mn3O4, often written as Mn2+Mn3+2O4 to reflect its mixed manganese valence states. It crystallizes in the tetragonal system and typically occurs as dark, metallic-looking crystals; more commonly, it appears as black to brownish-black masses. Hausmannite has a vitreous to submetallic luster, a Mohs hardness of 5.5 to 6, and a specific gravity around 4.8 to 5.0. It shows no distinct cleavage and often breaks with a conchoidal fracture.

Occurrence and associations: Hausmannite forms in oxidized zones of manganese-rich ore deposits and in hydrothermal veins. It is commonly associated with other manganese oxides and carbonates such as pyrolusite, manganite, braunite, and psilomelane. Crystals are relatively rare; it more often occurs as coarse to fine-grained masses or aggregates.

Structure and composition: The mineral has a spinel-like arrangement with Mn2+ occupying tetrahedral sites and Mn3+ occupying octahedral sites, giving it a mixed-valence Mn2+/Mn3+ composition that distinguishes it from single-valence manganese oxides.

Uses and significance: Hausmannite is an important but typically minor source of manganese in some ore deposits and is valued by mineral collectors for its distinctive tetragonal crystals. It is used in studying manganese oxide mineralogy and ore formation.