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. Calvertite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Calvertite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: cubic. Typical habit: platy crystals, crusts.
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 light green; luster reads metallic on Calvertite and vitreous on Malachite.
How to tell apart: Streak differs, so Calvertite leaves black, Azurite leaves light blue; luster reads metallic on Calvertite and vitreous to dull 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
- Platy Crystals, Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Copper Ore Deposits
Where rockhounds find calvertite
Classic worldwide localities
- Tsumeb mine, Namibia
Field-hunting tip
Look in oxidized copper ore deposits country, the host setting where calvertite typically forms. If you start seeing malachite, azurite, goethite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find calvertite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
