Dumortierite is a beautiful fibrous mineral best known for its deep denim-blue or violet coloration. It is often found as dense, massive aggregates in metamorphic rocks, making it a favorite for lapidary work and cabochon cutting.
Is this dumortierite?
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 dumortierite with a known reference. Dumortierite sits at Mohs 7-8.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Dumortierite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Dumortierite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, violet-blue, reddish-brown, greenish-blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, massive, or as acicular prismatic crystals.
Often confused with
Dumortierite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Dumortierite is noticeably harder (Mohs 7-8.5 vs. 5.5-6).
How to tell apart: Dumortierite is noticeably harder (Mohs 7-8.5 vs. 5-5.5); streak differs — Dumortierite leaves white, Lazurite leaves light blue.
Often found alongside dumortierite
Minerals reported to co-occur with dumortierite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₇(BO₃)(SiO₄)₃O₃
- Mohs hardness
- 7-8.5
- Density
- 3.3-3.4 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Massive, Or as Acicular Prismatic Crystals
- Cleavage
- Distinct in One Direction
- Rarity
- Uncommon
- Uses
- Collector, Lapidary, Decorative
- Host rock
- Aluminum-rich Metamorphic Rocks, Pegmatites
- Typical price
- $5-50 for small specimens, $100+ for high-quality clusters or carvings
Where rockhounds find dumortierite
3 mapped spotsClassic worldwide localities
- France
- Namibia
- USA (Nevada)
- Brazil
- Madagascar
Field-hunting tip
Look in aluminum-rich metamorphic rocks, pegmatites country — that is the host setting where dumortierite typically forms. If you start seeing quartz, muscovite, kyanite in float, you are in the right ground. Field specimens usually show a fibrous, massive, or as acicular prismatic crystals habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico, Montana — start trip planning there.
Common questions
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Find dumortierite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
