Eugsterite is a rare hydrated sulfate mineral typically found as efflorescent crusts or fine acicular needles in ephemeral saline lake environments. It is chemically unstable under varying humidity conditions and is best preserved in sealed containers to prevent dehydration.
Is this eugsterite?
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 eugsterite with a known reference. Eugsterite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Eugsterite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Eugsterite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular crystals, efflorescent crusts.
Often confused with
Eugsterite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside eugsterite
Minerals reported to co-occur with eugsterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Ca(SO₄)₂·2H₂O
- Mohs hardness
- 2.5
- Density
- 2.51 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular Crystals, Efflorescent Crusts
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Evaporite Deposits in Saline Lakes
- Typical price
- $50-300 per specimen
Where rockhounds find eugsterite
Classic worldwide localities
- Lake Magadi, Kenya
- Salina de la Laguna Verde, Argentina
- Death Valley, California, USA
Field-hunting tip
Look in evaporite deposits in saline lakes country — that is the host setting where eugsterite typically forms. If you start seeing halite, thenardite, gypsum in float, you are in the right ground. Field specimens usually show a acicular crystals, efflorescent crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find eugsterite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
