Geminite is a rare copper-arsenic mineral that typically forms delicate, grass-green sprays or radiating acicular crystals. It is primarily found in the oxidation zones of ore deposits where it is often associated with other copper-arsenic secondary minerals. Collectors prize it for its vibrant green color and delicate crystal habit, though it is often small and fragile.
Is this geminite?
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 geminite with a known reference. Geminite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Geminite leaves a pale green streak.
- 3Read the lusterHold the specimen under a strong light. Geminite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: emerald green, grass green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular or fibrous crystals, radial aggregates.
Often confused with
Geminite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Malachite is the harder of the two (Mohs 3.5-4 vs. 2); streak differs — Geminite leaves pale green, Malachite leaves light green.
How to tell apart: Conichalcite is the harder of the two (Mohs 4.5 vs. 2); streak differs — Geminite leaves pale green, Conichalcite leaves light green.
Often found alongside geminite
Minerals reported to co-occur with geminite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂AsO₃(OH)·H₂O
- Mohs hardness
- 2
- Density
- 3.2 g/cm³
- Colors
- Streak
- Pale Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Acicular or Fibrous Crystals, Radial Aggregates
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Copper-arsenic Deposits
- Typical price
- $20-200 per specimen depending on quality
Where rockhounds find geminite
Classic worldwide localities
- Gold Hill Mine, Utah, USA
- Tsumeb, Namibia
Field-hunting tip
Look in oxidized zones of copper-arsenic deposits country — that is the host setting where geminite typically forms. If you start seeing olivenite, cornwallite, azurite in float, you are in the right ground. Field specimens usually show a acicular or fibrous crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find geminite on the map
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