Hausmannite Identification Guide
Identifying hausmannite, a manganese oxide, by its brownish-black color, chestnut-brown streak, hardness, density, and difference from other Mn-Fe oxides.
Read the full Hausmannite encyclopedia entry →
What Hausmannite Looks Like
Hausmannite is a manganese oxide (Mn²⁺Mn³⁺₂O₄, a spinel-group oxide) and an important manganese ore. It is brownish-black to black with a submetallic luster and is opaque. Well-formed crystals are pseudo-octahedral, often steeply pyramidal, and may show striations; more commonly it occurs granular or massive. A key distinguishing feature is its chestnut-brown streak, unusual among the dark manganese oxides.
- Color: brownish-black to black
- Transparency: opaque
- Luster: submetallic
- Habit: pseudo-octahedral crystals, granular, massive aggregates
Step-by-Step Field-ID Checklist
- Streak test first. Scrape on unglazed porcelain — hausmannite gives a distinctive chestnut/reddish-brown streak, not black.
- Check luster. Submetallic, slightly dull rather than bright metallic.
- Test hardness. It scratches with a knife only with difficulty (around 5.5).
- Heft it. It feels heavy (high specific gravity).
- Note crystal form/setting. Pseudo-octahedral crystals in metamorphosed manganese deposits or hydrothermal veins support the ID.
Key Diagnostic Tests
- Mohs hardness: ~5.5 — harder than many soft Mn oxides (e.g., pyrolusite).
- Streak: chestnut/reddish-brown — the standout diagnostic.
- Cleavage: nearly perfect basal cleavage.
- Specific gravity: ~4.8 — distinctly heavy.
- Magnetism: weakly to non-magnetic (less than magnetite).
- Acid: dissolves in hydrochloric acid, releasing chlorine (a manganese-mineral behavior).
Common Look-Alikes and How to Tell Them Apart
- Pyrolusite (MnO₂): soft (1–2 when massive), sooty black streak, often marks the fingers; hausmannite is harder with a brown streak.
- Magnetite (Fe₃O₄): strongly magnetic with a black streak; hausmannite is weakly magnetic at most and has a brown streak.
- Hematite: red-brown streak too, but typically lower hardness varieties differ and hematite is iron, not manganese; hausmannite's streak is more chestnut and its crystals pseudo-octahedral.
- Braunite / bixbyite: other dark Mn oxides — distinguished by streak color, hardness, and crystal habit, often needing lab confirmation.
- Franklinite: spinel-group like hausmannite but more octahedral, brown-black streak, found mainly at Franklin, NJ with zinc minerals.
The most reliable single clue is the chestnut-brown streak combined with high SG (~4.8) and hardness ~5.5.
Where Hausmannite Is Found
Hausmannite forms in high-temperature hydrothermal veins and in metamorphosed manganese deposits. World-class crystals come from the Kalahari Manganese Field, South Africa (notably N'Chwaning and Wessels mines), with classic occurrences at Öhrenstock, Germany (the type area), Sweden (Långban), and India.
Quick Field Summary
A heavy, brownish-black, submetallic manganese oxide with pseudo-octahedral crystals, a hardness near 5.5, and a telltale chestnut-brown streak is hausmannite — separated from soft black-streaked pyrolusite and strongly magnetic magnetite.
Frequently asked questions
How do you identify hausmannite?
Identify hausmannite by its brownish-black submetallic appearance, pseudo-octahedral crystals, hardness around 5.5, high specific gravity (~4.8), and especially its distinctive chestnut-brown streak.
What color is hausmannite's streak?
Hausmannite gives a chestnut or reddish-brown streak, which is unusual among dark manganese oxides and helps separate it from black-streaked minerals like pyrolusite and magnetite.
What is the difference between hausmannite and pyrolusite?
Pyrolusite is a soft manganese dioxide (often 1–2 in hardness) with a sooty black streak that marks the fingers, while hausmannite is harder (~5.5) with a chestnut-brown streak and pseudo-octahedral crystals.
Is hausmannite magnetic?
Hausmannite is at most weakly magnetic, far less than magnetite. This weak response, combined with its brown streak, helps distinguish it from strongly magnetic iron oxides.