Tangdanite is a rare hydrated copper phosphate mineral typically found as small tabular blue to blue-green crystals in oxidized zones of copper deposits. It was first described from the Tangdan Mine in China and is highly prized by micromounters and advanced mineral collectors for its vibrant color.
Is this tangdanite?
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 tangdanite with a known reference. Tangdanite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light green.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly to silky.
- 4Match the color rangeCompare against the expected color range: emerald-green, dark green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, crusts, pulverulent aggregates.
Often confused with
Tangdanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Turquoise is the harder of the two (Mohs 5-6 vs. 2-2.5); streak differs, so Tangdanite leaves light green, Turquoise leaves white to pale greenish blue; luster reads pearly to silky on Tangdanite and vitreous in crystals; dull to waxy if massive on Turquoise.
How to tell apart: Libethenite is the harder of the two (Mohs 4 vs. 2-2.5); luster reads pearly to silky on Tangdanite and vitreous, greasy on fracture surfaces on Libethenite.
How to tell apart: Pseudomalachite is the harder of the two (Mohs 4.5-5 vs. 2-2.5); streak differs, so Tangdanite leaves light green, Pseudomalachite leaves pale green to pale bluish green; luster reads pearly to silky on Tangdanite and vitreous to resinous on Pseudomalachite.
Often found alongside tangdanite
Minerals reported to co-occur with tangdanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Cu₉(AsO₄)₄(SO₄)₀.₅(OH)₉·9H₂O
- Mohs hardness
- 2-2.5
- Density
- 3.22 g/cm³
- Colors
- Streak
- Light green
- Luster
- Pearly to silky
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, crusts, pulverulent aggregates
- Cleavage
- Perfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the oxidized zone of an As-bearing Cu sulfide deposit
Where rockhounds find tangdanite
Classic worldwide localities
- Tangdan and Nanniping mines, southeast Dongchuan district, Dongchuan County, Kunming City Prefecture, Yunnan Province, P.R. China
Field-hunting tip
Where it forms: A secondary mineral in the oxidized zone of an As-bearing Cu sulfide deposit. If you start seeing chalcopyrite, bornite, chalcocite in float, you are in the right ground. Typical habit: tabular crystals, crusts, pulverulent aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tangdanite on the map
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