Lecontite is a very rare ammonium-sodium sulfate mineral that typically forms as an efflorescent crust in environments rich in organic matter, such as bat caves. Collectors should look for its characteristic tabular crystal habit or thin white crusts, though it is highly soluble and unstable if exposed to changing humidity.
Is this lecontite?
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 lecontite with a known reference. Lecontite sits at Mohs 2-2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Lecontite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Lecontite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellowish-white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, massive, crusts.
Often confused with
Lecontite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside lecontite
Minerals reported to co-occur with lecontite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄,K)NaSO₄·2H₂O
- Mohs hardness
- 2-2.5
- Density
- 1.79 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Massive, Crusts
- Cleavage
- Distinct On {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Evaporite Deposits, Bat Guano Caves
- Typical price
- $20-150 for thumbnail specimens
Where rockhounds find lecontite
Classic worldwide localities
- Lavours, Ain, France
- Gila Bend, Arizona, USA
- Sodaville, Nevada, USA
Field-hunting tip
Look in evaporite deposits, bat guano caves country — that is the host setting where lecontite typically forms. If you start seeing mirabilite, thenardite, gypsum in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find lecontite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
