Gregoryite is a rare alkali carbonate mineral found almost exclusively in the unique natrocarbonatite lavas of Oldoinyo Lengai. It is highly unstable upon exposure to moisture and air, often altering rapidly into other carbonates, which makes preservation difficult for collectors.
Is this gregoryite?
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 gregoryite with a known reference. Gregoryite sits at Mohs 5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gregoryite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gregoryite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, pale yellow.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: granular, massive, rarely as small hexagonal crystals.
Often confused with
Gregoryite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside gregoryite
Minerals reported to co-occur with gregoryite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na₂CO₃,K₂CO₃,CaCO₃)
- Mohs hardness
- 5
- Density
- 2.44 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Hexagonal
- Crystal habit
- Granular, Massive, Rarely as Small Hexagonal Crystals
- Cleavage
- None Observed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Natrocarbonatite Lava
- Typical price
- $50-500 depending on specimen quality
Where rockhounds find gregoryite
Classic worldwide localities
- Oldoinyo Lengai, Tanzania
Field-hunting tip
Look in natrocarbonatite lava country — that is the host setting where gregoryite typically forms. If you start seeing nyerereite, sylvite, halite in float, you are in the right ground. Field specimens usually show a granular, massive, rarely as small hexagonal crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gregoryite on the map
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