Hausmannite

Hausmannite is a manganese oxide with mixed valence (Mn2+Mn3+2O4), an important ore of manganese. It is typically brownish-black to black with a submetallic luster and forms pseudo-octahedral crystals in the tetragonal system.

Named after the German mineralogist Johann Friedrich Ludwig Hausmann, it is distinguished from many other black manganese oxides by its chestnut-brown streak. Crystals are often striated and may show twinning.

It occurs both in high-temperature hydrothermal and metamorphic manganese deposits, and as a product of altered manganese ores, frequently in massive granular form as well as in good crystals.

Hausmannite forms in high-temperature hydrothermal veins, in contact and regional metamorphic manganese deposits, and as a secondary alteration product of other manganese minerals. It is a primary constituent of many metamorphosed manganese ore bodies.

It commonly occurs with braunite, manganite, pyrolusite, jacobsite, and carbonates such as rhodochrosite and calcite. Famous localities include Langban in Sweden, the Kalahari manganese field in South Africa (notably N'Chwaning and Wessels mines), Ilfeld in Germany, and various manganese districts in India.

Key clues are a brownish-black to black color, submetallic luster, and especially a chestnut-brown streak, which distinguishes it from black manganese oxides that give black streaks. Hardness is moderate (Mohs about 5.5), and crystals are pseudo-octahedral, often striated.

Look-alikes include magnetite (magnetic, black streak), braunite (harder, brownish-black streak too), and pyrolusite (much softer, sooty black). The combination of pseudo-octahedral habit, moderate hardness, and brown streak in a manganese-rich setting is the best field guide.

Hausmannite is a valuable ore of manganese, a metal essential to steelmaking, where manganese improves strength and removes oxygen and sulfur. Manganese is also used in batteries, aluminum alloys, and chemicals, so manganese oxide ores like hausmannite have significant economic value.

Fine crystallized specimens, especially the lustrous crystals from the Kalahari manganese field, are also prized by collectors. It has no gemstone use and little metaphysical tradition; its importance is chiefly industrial and mineralogical.