Alstonite is a rare barium-calcium carbonate that frequently forms complex pseudo-hexagonal twinned crystals. Collectors primarily find it in low-temperature hydrothermal veins, where it is often associated with witherite and fluorite. It is best identified by its distinct fluorescence and its typical twinning habits which create triangular striations on crystal faces.
Is this alstonite?
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 alstonite with a known reference. Alstonite sits at Mohs 4-4.5, 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: colorless, gray, white, pink.
- 5Look at form & habitCrystal system: triclinic. Typical habit: euhedral crystals, pseudo hexagonal.
Often confused with
Alstonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside alstonite
Minerals reported to co-occur with alstonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaBa(CO₃)₂
- Mohs hardness
- 4-4.5
- Density
- 3.707 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Euhedral crystals, pseudo hexagonal
- Cleavage
- On pseudo-orthorhombic {110}, imperfect
- Fluorescence
- Weak yellow under LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Typically in low-temperature hydrothermal Pb–Zn deposits; rare in carbonatites
Where rockhounds find alstonite
1 mapped spotsClassic worldwide localities
- Minerva No. 1 mine, Cave-in-Rock, Hardin Co., Illinois, USA
- Bromley Hill Pb–Zn mine, near Alston, Cumbria, in the Fallowfield lead mine, near Hexham, Northumberland, and at New Brancepeth, Durham, England
- Mine BK-3, Llantrisant, 10 km north of Cardiff, Wales
- Vuoriyarvi carbonatite complex, Kola Peninsula, Russia
- Found in the Tajno borehole, 70 km north of Bialystok, Poland
- Garaoulère Zn–Pb orebody, Pierrefitte, Pyrénées, France
Field-hunting tip
Where it forms: Typically in low-temperature hydrothermal Pb–Zn deposits; rare in carbonatites. If you start seeing calcite, barite, ankerite in float, you are in the right ground. Typical habit: euhedral crystals, pseudo hexagonal. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Illinois. Start trip planning there.
Common questions
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Find alstonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
