Mirabilite is a hydrous sodium sulfate mineral that typically forms as white, crusty, or needle-like efflorescences in arid environments. It is notoriously unstable in open air, as it dehydrates rapidly to powdery thenardite when exposed to low humidity or warmth, so it must be stored in airtight containers.
Is this mirabilite?
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 mirabilite with a known reference. Mirabilite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mirabilite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mirabilite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellowish.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crystals, massive, granular crusts.
Often confused with
Mirabilite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside mirabilite
Minerals reported to co-occur with mirabilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂SO₄·10H₂O
- Mohs hardness
- 1.5-2
- Density
- 1.49 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crystals, Massive, Granular Crusts
- Cleavage
- Perfect On {100}
- Rarity
- Common
- Uses
- Collector, Scientific Study
- Host rock
- Evaporite Deposits, Playa Lakes, Volcanic Fumaroles
- Typical price
- $10-50 per specimen
Where rockhounds find mirabilite
1 mapped spotsClassic worldwide localities
- Great Salt Lake (USA)
- Salton Sea (USA)
- Ischl (Austria)
- Siberia (Russia)
Field-hunting tip
Look in evaporite deposits, playa lakes, volcanic fumaroles country — that is the host setting where mirabilite typically forms. If you start seeing halite, thenardite, gypsum in float, you are in the right ground. Field specimens usually show a acicular crystals, massive, granular crusts habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah — start trip planning there.
Common questions
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Find mirabilite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
