Boromullite is a rare boron-bearing mineral closely related to the dumortierite group, occurring as colorless to white prismatic crystals. It is primarily found in high-grade metamorphic environments, often associated with sillimanite-bearing assemblages. Because of its extreme rarity, it is essentially restricted to advanced mineral collections and professional study.
Is this boromullite?
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 boromullite with a known reference. Boromullite 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. Boromullite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Boromullite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals.
Often confused with
Boromullite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside boromullite
Minerals reported to co-occur with boromullite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₉BSi₃O₁₉
- Mohs hardness
- 7
- Density
- 3.35 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $50-300+ thumbnail
Where rockhounds find boromullite
Classic worldwide localities
- Kola Peninsula, Russia
Field-hunting tip
Look in metamorphic rocks country — that is the host setting where boromullite typically forms. If you start seeing sillimanite, corundum, kyanite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find boromullite on the map
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