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 1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly on cleavages.
- 4Match the color rangeCompare against the expected color range: green, blue green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates.
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 4-4.5 vs. 1.5); luster reads pearly on cleavages on Theisite and subadamantine to silky in aggregates on Austinite.
How to tell apart: Conichalcite is the harder of the two (Mohs 4.5 vs. 1.5); streak differs, so Theisite leaves white, Conichalcite leaves green; luster reads pearly on cleavages on Theisite and vitreous to somewhat greasy 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
- Cu₅Zn₅As₂O₈(OH)₁₄
- Mohs hardness
- 1.5
- Density
- 4.3 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly on cleavages
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in thin seams cutting other oxidized minerals (near Durango, Colorado, USA); in dolomitized marble (Forno, Italy)
Where rockhounds find theisite
Classic worldwide localities
- Tucker’s tunnel uranium deposit, near Durango, Hinsdale Co., Colorado, USA
- Tynagh mine, near Loughrea, Co. Galway, Ireland
- Glücksrad mine, Oberschulenberg, Harz Mountains, Germany
- Richelsdorf Mountains, Hesse, Germany
- Clara mine, near Oberwolfach, Black Forest, Germany
- Padern, Pyrénées-Orientales, France
Field-hunting tip
Where it forms: A rare secondary mineral in thin seams cutting other oxidized minerals (near Durango, Colorado, USA); in dolomitized marble (Forno, Italy). If you start seeing cuprite, malachite, azurite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify theisite?+
Where is theisite found?+
Is theisite safe to handle?+
What rocks look like theisite?+
What minerals are found with theisite?+
What kind of rock does theisite form in?+
What is theisite used for?+
Find theisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
