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 1-2, 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: greasy.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: efflorescences, encrustations, water soluble.
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·18H₂O
- Mohs hardness
- 1-2
- Density
- 1.58 g/cm³
- Streak
- White
- Luster
- Greasy
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Efflorescences, encrustations, water soluble
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare post-mine mineral deposited from solutions derived from an oxidizing breccia zone (Lone Pine mine, New Mexico, USA)
Where rockhounds find wilcoxite
Classic worldwide localities
- Lone Pine mine, Wilcox district, near Silver City, Catron Co., New Mexico, USA
- Deputatskoye tin deposit, northeast Sakha, Russia
- Valle del Cura, San Juan Province, Argentina
Field-hunting tip
Where it forms: A rare post-mine mineral deposited from solutions derived from an oxidizing breccia zone (Lone Pine mine, New Mexico, USA). If you start seeing fluorite, gypsum, khademite in float, you are in the right ground. Typical habit: efflorescences, encrustations, water soluble. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify wilcoxite?+
Where is wilcoxite found?+
What rocks look like wilcoxite?+
What minerals are found with wilcoxite?+
What kind of rock does wilcoxite form in?+
What is wilcoxite used for?+
Find wilcoxite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
