Leonardsenite is a rare magnesium fluoride mineral discovered in the Leonard Mine in Butte, Montana. It typically occurs as small, colorless platy crystals associated with quartz and fluorite in mine dump environments.
Is this leonardsenite?
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 leonardsenite with a known reference. Leonardsenite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy (aggregates).
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals.
Often confused with
Leonardsenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sellaite is the harder of the two (Mohs 5-5.5 vs. 2); luster reads earthy (aggregates) on Leonardsenite and vitreous on Sellaite.
How to tell apart: Luster reads earthy (aggregates) on Leonardsenite and vitreous on Villiaumite.
Often found alongside leonardsenite
Minerals reported to co-occur with leonardsenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgAlF₅(H₂O)₂
- Mohs hardness
- 2
- Density
- 2.31 g/cm³
- Colors
- Streak
- White
- Luster
- Earthy (aggregates)
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A sublimated encrustations from fluorine-rich fumarolic gas
Where rockhounds find leonardsenite
Classic worldwide localities
- Leonard Mine, Butte, Montana, USA
Field-hunting tip
Where it forms: A sublimated encrustations from fluorine-rich fumarolic gas. If you start seeing jakobssonite, anhydrite, ralstonite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find leonardsenite on the map
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