Boralsilite is an exceptionally rare borosilicate mineral typically found as tiny, colorless prismatic crystals. It was originally discovered in ejected limestone blocks within volcanic tuff, making it a highly sought-after specimen for advanced mineral collectors focusing on rare species.
Is this boralsilite?
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 boralsilite with a known reference. Boralsilite sits at Mohs 7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Boralsilite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Boralsilite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, radial aggregates.
Often confused with
Boralsilite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside boralsilite
Minerals reported to co-occur with boralsilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₁₆B₆Si₂O₃₇
- Mohs hardness
- 7
- Density
- 3.37 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Radial Aggregates
- Cleavage
- None Observed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Limestone Xenoliths
- Typical price
- $100-500 for small micros
Where rockhounds find boralsilite
Classic worldwide localities
- Capo di Bove, Rome, Italy
Field-hunting tip
Look in metamorphosed limestone xenoliths country — that is the host setting where boralsilite typically forms. If you start seeing sillimanite, corundum, spinel in float, you are in the right ground. Field specimens usually show a prismatic crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find boralsilite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
