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?
3-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.
- 2Match the color rangeCompare against the expected color range: white.
- 3Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic.
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
- Al₉BSi₂O₁₉
- Mohs hardness
- 7
- Density
- 3.081 g/cm³
- Colors
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Product of granulite facies metamorphism of boron-rich peletic rocks
Where rockhounds find boromullite
Classic worldwide localities
- Mount Stafford, ~170 km northwest of Alice Springs, central Australia
Field-hunting tip
Where it forms: Product of granulite facies metamorphism of boron-rich peletic rocks. If you start seeing sillimanite, werdingite, sekaninaite-cordierite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify boromullite?+
Where is boromullite found?+
What rocks look like boromullite?+
What minerals are found with boromullite?+
What kind of rock does boromullite form in?+
What is boromullite used for?+
Find boromullite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
