Bentorite is a very rare member of the ettringite group typically found as small, delicate, pinkish-violet prismatic crystals. It is primarily known from its type locality in the Hatrurim Basin of Israel, occurring in high-temperature metamorphic environments. Due to its softness and high water content, specimens should be handled with care and stored in a low-humidity environment.
Is this bentorite?
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 bentorite with a known reference. Bentorite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: very pale violet.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: violet, light violet.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: prismatic crystals.
Often confused with
Bentorite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Bentorite leaves very pale violet, Ettringite leaves white.
How to tell apart: Thaumasite is the harder of the two (Mohs 3.5 vs. 2); streak differs, so Bentorite leaves very pale violet, Thaumasite leaves white.
Often found alongside bentorite
Minerals reported to co-occur with bentorite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆Cr₂(SO₄)₃(OH)₁₂·26H₂O
- Mohs hardness
- 2
- Density
- 2.025 g/cm³
- Colors
- Streak
- Very pale violet
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Hexagonal
- Crystal habit
- Prismatic crystals
- Cleavage
- {1010}, perfect; {0001}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In low-temperature hydrothermal veins in black calcite–spurrite marble
Where rockhounds find bentorite
1 mapped spotsClassic worldwide localities
- Marble quarry in the Hatrurim Formation, near the Arad-Sodom road, Negev Desert, Israel (type locality)
Field-hunting tip
Where it forms: In low-temperature hydrothermal veins in black calcite–spurrite marble. If you start seeing calcite, thaumasite, truscottite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah. Start trip planning there.
Common questions
How do you identify bentorite?+
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Can I find bentorite in the United States?+
What rocks look like bentorite?+
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Find bentorite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
