Gaylussite is a relatively soft, hydrated sodium calcium carbonate mineral typically found in evaporite lake deposits. It is known for its distinctive wedge-shaped, monoclinic crystal habit and its tendency to dehydrate into powdery white coatings if not kept in a stable environment.
Is this gaylussite?
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 gaylussite with a known reference. Gaylussite 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. Streak: white to pale gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, gray, gray white, yellow, yellowish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: disseminated, tabular.
Often confused with
Gaylussite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gaylussite
Minerals reported to co-occur with gaylussite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Ca(CO₃)₂·5H₂O
- Mohs hardness
- 2.5-3
- Density
- 1.991 g/cm³
- Streak
- White to pale gray
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Disseminated, tabular
- Cleavage
- On {110}, perfect; on {001}, imperfect
- Fluorescence
- Blue-white under LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Typically in evaporites or shales from alkali lakes; rarely in veinlets cutting alkalic igneous rocks
Where rockhounds find gaylussite
Classic worldwide localities
- Mono Lake, Mono Co., Borax Lake, Lake Co., Deep Spring Lake, Inyo Co., China Lake, Kern Co., and Searles Lake, San Bernardino Co., California, USA
- Green River Formation, Sweetwater Co., Wyoming, USA
- Lagunillas, 80 km southeast of Mérida, Venezuela
- Lake Amboseli, Kenya
- Lake Eyasi, Tanzania
- Zoutpan Farm, 40 km northwest of Pretoria, Transvaal, South Africa
Field-hunting tip
Where it forms: Typically in evaporites or shales from alkali lakes; rarely in veinlets cutting alkalic igneous rocks. If you start seeing shortite, northupite, pirssonite in float, you are in the right ground. Typical habit: disseminated, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gaylussite?+
Where is gaylussite found?+
What rocks look like gaylussite?+
What minerals are found with gaylussite?+
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What is gaylussite used for?+
Find gaylussite on the map
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