Marécottite is a rare uranyl sulfate mineral found primarily in the French-Swiss border region. It typically forms small, vibrant yellow to orange-yellow tabular crystals in oxidized zones of uranium deposits. Collectors should treat it with extreme caution due to its significant radioactive content.
Is this marécottite?
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 marécottite with a known reference. Marécottite sits at Mohs 2-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Marécottite leaves a pale yellow streak.
- 3Read the lusterHold the specimen under a strong light. Marécottite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange-yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Marécottite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Marécottite and pearly on Autunite.
How to tell apart: Streak differs — Marécottite leaves pale yellow, Meta-autunite leaves yellow; luster reads vitreous on Marécottite and pearly on Meta-autunite.
Often found alongside marécottite
Minerals reported to co-occur with marécottite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₃(UO₂)₈(SO₄)₄(OH)₁₀·28H₂O
- Mohs hardness
- 2-3
- Density
- 3.85 g/cm³
- Colors
- Streak
- Pale Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- None
- Fluorescence
- Bright Yellow-green Under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Vein Deposits
- Typical price
- $50-300+ depending on crystal size and specimen quality
Where rockhounds find marécottite
Classic worldwide localities
- Marecottes, Valais, Switzerland
Field-hunting tip
Look in hydrothermal vein deposits country — that is the host setting where marécottite typically forms. If you start seeing uraninite, gypsum, jarosite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find marécottite on the map
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