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, so 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, 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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