Calvertite is a rare copper germanium sulfide, typically black. It occurs in a highly oxidized, polymetallic, fractured and brecciated dolomite and sandstone pipe. Associated minerals include reinerite, tennantite and gallite. It was first described from Tsumeb mine, Namibia.
Is this calvertite?
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 calvertite with a known reference. Calvertite sits at Mohs 4-5, 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: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: cubic. Typical habit: granular.
Often confused with
Calvertite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Calvertite leaves black, Malachite leaves pale green; luster reads metallic on Calvertite and adamantine to vitreous; silky if fibrous; dull to earthy if massive on Malachite.
How to tell apart: Streak differs, so Calvertite leaves black, Azurite leaves pale blue; luster reads metallic on Calvertite and vitreous to subadamantine on Azurite.
Often found alongside calvertite
Minerals reported to co-occur with calvertite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₅Ge₀.₅S₄
- Mohs hardness
- 4-5
- Density
- 5.239 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Granular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a highly oxidized, polymetallic, fractured and brecciated dolomite and sandstone pipe
Where rockhounds find calvertite
Classic worldwide localities
- Tsumeb mine, Namibia
Field-hunting tip
Where it forms: In a highly oxidized, polymetallic, fractured and brecciated dolomite and sandstone pipe. If you start seeing reinerite, tennantite, gallite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify calvertite?+
Where is calvertite found?+
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What rocks look like calvertite?+
What minerals are found with calvertite?+
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Find calvertite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
