Thenardite is an anhydrous sodium sulfate mineral that typically forms in arid lake environments. It is often found as crusts or prismatic crystals, but collectors should note that it is metastable and may transform into mirabilite if exposed to high humidity.
Is this thenardite?
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 thenardite with a known reference. Thenardite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thenardite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Thenardite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, grayish, yellowish.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, massive, crusts.
Often confused with
Thenardite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside thenardite
Minerals reported to co-occur with thenardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂SO₄
- Mohs hardness
- 2.5-3
- Density
- 2.66 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Massive, Crusts
- Cleavage
- Distinct On {001}
- Rarity
- Common
- Uses
- Industrial, Collector
- Host rock
- Evaporite Deposits
- Typical price
- $5-30 for small to cabinet specimens
Where rockhounds find thenardite
Classic worldwide localities
- Searles Lake, California, USA
- Chile
- Spain
- Lake Magadi, Kenya
Field-hunting tip
Look in evaporite deposits country — that is the host setting where thenardite typically forms. If you start seeing mirabilite, halite, gypsum in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find thenardite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
