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, 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
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
