Theisite is a rare copper-zinc arsenate mineral typically found as small, apple-green to yellow-green platy crystals or rosettes. It is most famous for its occurrences in the oxidation zone of the Tsumeb Mine in Namibia, where it forms in association with other rare secondary minerals.
Is this theisite?
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 theisite with a known reference. Theisite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Theisite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Theisite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: green, yellow-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy, rosette-like aggregates, microcrystalline.
Often confused with
Theisite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Austinite is the harder of the two (Mohs 4 vs. 2.5); luster reads pearly on Theisite and vitreous on Austinite.
How to tell apart: Conichalcite is the harder of the two (Mohs 4.5 vs. 2.5); streak differs — Theisite leaves white, Conichalcite leaves light green; luster reads pearly on Theisite and vitreous on Conichalcite.
Often found alongside theisite
Minerals reported to co-occur with theisite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₅Zn₅(AsO₄)₂(OH)₁₀
- Mohs hardness
- 2.5
- Density
- 5.3 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy, Rosette-like Aggregates, Microcrystalline
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Polymetallic Hydrothermal Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find theisite
Classic worldwide localities
- Tsumeb Mine, Namibia
Field-hunting tip
Look in oxidized zones of polymetallic hydrothermal deposits country — that is the host setting where theisite typically forms. If you start seeing tsumcorite, smithsonite, arseniosiderite in float, you are in the right ground. Field specimens usually show a platy, rosette-like aggregates, microcrystalline habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find theisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
