Vajdakite is a rare secondary mineral typically found as small, gray-green to grass-green tabular crystals in oxidation zones of uranium-molybdenum deposits. It is primarily known from the historic mining district of Jáchymov, where it forms in association with uranium minerals. Collectors value it for its vibrant color and rarity, often requiring magnification for proper identification.
Is this vajdakite?
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 vajdakite with a known reference. Vajdakite 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 to light gray-green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: green, greenish gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, aggregates.
Often confused with
Vajdakite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Molybdite is the harder of the two (Mohs 3-4 vs. 2); luster reads vitreous on Vajdakite and adamantine on Molybdite.
How to tell apart: Streak differs, so Vajdakite leaves white to light gray-green, Ferrimolybdite leaves pale yellow; luster reads vitreous on Vajdakite and adamantine to silky, earthy on Ferrimolybdite.
Often found alongside vajdakite
Minerals reported to co-occur with vajdakite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mo⁶⁺O₂)₂As³⁺₂O₅·3H₂O
- Mohs hardness
- 2
- Density
- 3.50 g/cm³
- Colors
- Streak
- White to light gray-green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, aggregates
- Cleavage
- {100} perfect, {010} good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in a highly oxidized uraninite-arsenide-sulfarsenide deposit (Czech Republic)
Where rockhounds find vajdakite
Classic worldwide localities
- Geschieber vein on the 12th level, Svornost mine, Jáchymov (St. Joachimsthal), ~20 km north of Karlovy Vary, northwestern Bohemia, Czech Republic
Field-hunting tip
Where it forms: A rare secondary mineral in a highly oxidized uraninite-arsenide-sulfarsenide deposit (Czech Republic). If you start seeing arsenolite, scorodite, parascorodite in float, you are in the right ground. Typical habit: acicular, aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify vajdakite?+
Where is vajdakite found?+
Is vajdakite safe to handle?+
What rocks look like vajdakite?+
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Find vajdakite on the map
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