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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white.
- 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
- Mohs hardness
- 5
- Density
- 2.27 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
- Crystal habit
- Granular, massive, rarely as small hexagonal crystals
- Cleavage
- None observed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As phenocrysts in lengaite carbonatite lava
Where rockhounds find gregoryite
Classic worldwide localities
- Oldoinyo Lengai volcano, Tanzania
Field-hunting tip
Where it forms: As phenocrysts in lengaite carbonatite lava. If you start seeing nyerereite, alabandite, halite in float, you are in the right ground. Typical habit: granular, massive, rarely as small hexagonal crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gregoryite?+
Where is gregoryite found?+
What rocks look like gregoryite?+
What minerals are found with gregoryite?+
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Find gregoryite on the map
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