Wilcoxite is an extremely rare, water-soluble sulfate mineral that typically forms as delicate, white efflorescent crusts on shale surfaces. It is primarily known from specific cave environments where it deposits due to the interaction of weathering minerals. Collectors should handle specimens with care to prevent dehydration or damage to the fragile crystal structures.
Is this wilcoxite?
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 wilcoxite with a known reference. Wilcoxite 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. Wilcoxite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Wilcoxite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: crusts, efflorescent aggregates.
Often confused with
Wilcoxite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside wilcoxite
Minerals reported to co-occur with wilcoxite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgAl(SO₄)₂F·17H₂O
- Mohs hardness
- 2
- Density
- 1.87 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Crusts, Efflorescent Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Shale
- Typical price
- variable depending on specimen quality and size, typically found in research collections
Where rockhounds find wilcoxite
Classic worldwide localities
- Alum Cave Bluff, Great Smoky Mountains, Tennessee, USA
Field-hunting tip
Look in shale country — that is the host setting where wilcoxite typically forms. If you start seeing epsomite, halotrichite, gypsum in float, you are in the right ground. Field specimens usually show a crusts, efflorescent aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find wilcoxite on the map
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