Brunogeierite is an extremely rare germanium-bearing mineral belonging to the spinel group. It is primarily found as microscopic octahedral crystals associated with lead-zinc ores at the Tsumeb mine in Namibia.
Is this brunogeierite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch brunogeierite with a known reference. Brunogeierite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: gray, black.
- 5Look at form & habitCrystal system: cubic. Typical habit: encrustations.
Often confused with
Brunogeierite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads submetallic on Brunogeierite and metallic to submetallic, may be dull on Magnetite.
How to tell apart: Franklinite is the harder of the two (Mohs ~6 vs. 5); streak differs, so Brunogeierite leaves black, Franklinite leaves reddish brown to black; luster reads submetallic on Brunogeierite and metallic to semimetallic; may be dull on Franklinite.
Often found alongside brunogeierite
Minerals reported to co-occur with brunogeierite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂GeO₄
- Mohs hardness
- 5
- Density
- 5.51 g/cm³
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Encrustations
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the lower oxidation zone of a dolostone-hosted hydrothermal polymetallic ore deposit, at a depth of 930 meters (Tsumeb, Namibia)
Where rockhounds find brunogeierite
Classic worldwide localities
- Tsumeb, Namibia
- Central Pyrénées, as at Cauflens, Ariège, France
- Carboire, Couledoux, Estaing, and Pal Bidao, Haute-Garonne, France
Field-hunting tip
Where it forms: In the lower oxidation zone of a dolostone-hosted hydrothermal polymetallic ore deposit, at a depth of 930 meters (Tsumeb, Namibia). If you start seeing tennantite, reniérite, zincian stottite in float, you are in the right ground. Typical habit: encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify brunogeierite?+
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What rocks look like brunogeierite?+
What minerals are found with brunogeierite?+
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Find brunogeierite on the map
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