Znucalite is a very rare secondary uranium-zinc carbonate mineral that forms as thin, pearly crusts or small platy crystals in oxidized zones. It is highly valued by mineral collectors for its distinct bright green fluorescence under shortwave ultraviolet light.
Is this znucalite?
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 znucalite with a known reference. Znucalite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: white, light yellow, grayish yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates, encrustations.
Often confused with
Znucalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Znucalite leaves white, Autunite leaves pale yellow; luster reads silky on Znucalite and vitreous, pearly on {001} on Autunite.
How to tell apart: Adamite is the harder of the two (Mohs 3.5 vs. 2); luster reads silky on Znucalite and vitreous on Adamite.
Often found alongside znucalite
Minerals reported to co-occur with znucalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₁₀Ca(UO₂)(CO₃)₄(OH)₁₆(H₂O)₅
- Mohs hardness
- 2
- Density
- 3.01-3.1 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates, encrustations
- Cleavage
- Perfect on {010}
- Fluorescence
- Greenish yellow under SW and LW UV
- Rarity
- Rare
- Uses
- Collector, Scientific study
- Host rock
- A rare secondary species at carbonate-hosted polymetallic veins, and nearby oxidizing uranium veins; on dump material and coating mine walls, apparently of post-mine origin
Where rockhounds find znucalite
Classic worldwide localities
- Lill mine, Příbram, and in the Evangelista and Ondřej veins, Jáchymov (Joachimsthal), Czech Republic
- Mas-d’Alary uranium deposit, three km south-southeast of Lodève, Hérault, France
- St. Christophe mine, near Bärenhecke, Saxony, Germany
Field-hunting tip
Where it forms: A rare secondary species at carbonate-hosted polymetallic veins, and nearby oxidizing uranium veins; on dump material and coating mine walls, apparently of post-mine origin. If you start seeing gypsum, hydrozincite, serpierite in float, you are in the right ground. Typical habit: aggregates, encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify znucalite?+
Where is znucalite found?+
Is znucalite safe to handle?+
What rocks look like znucalite?+
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Find znucalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
