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 1-2, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: efflorescences.
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
- Na₄Ca(SO₄)₃·2H₂O
- Mohs hardness
- 1-2
- Density
- 2.5 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Efflorescences
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As evaporative crusts in carbonate-poor soil, playa sediment and around an active boron-rich spring
Where rockhounds find eugsterite
Classic worldwide localities
- Eagle Borax Spring, Furnace Creek district, Death Valley, Inyo Co., California, USA
- Northeast of Karapinar, between Konya and Ereǧli, Great Konya Basin, Konya Province, Turkey
- Shore of Lake Victoria, at Sindo and Luanda, and at Kalacha, Turkana district, Kenya
- Schildmauer, near Admont, Styria, Austria
- Río Grande and Rincón playas, Jujuy Province, Argentina
Field-hunting tip
Where it forms: As evaporative crusts in carbonate-poor soil, playa sediment and around an active boron-rich spring. If you start seeing thénardite, halite, blödite in float, you are in the right ground. Typical habit: efflorescences. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify eugsterite?+
Where is eugsterite found?+
What rocks look like eugsterite?+
What minerals are found with eugsterite?+
What kind of rock does eugsterite form in?+
What is eugsterite used for?+
Find eugsterite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
