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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: blue, brown, violet, greenish blue, pink.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: columnar, fibrous, prismatic.
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, so Dumortierite leaves white, Lazurite leaves bright 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
- 3.21-3.41 g/cm³
- Streak
- White
- Luster
- Vitreous to dull
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Columnar, fibrous, prismatic
- Cleavage
- Distinct on {100}, poor on {110}; parting on {001}
- Rarity
- Uncommon
- Uses
- Collector, Lapidary, Decorative
- Host rock
- In aluminum-rich regionally metamorphosed rocks, disseminated and in veinlets cutting schists; also in pegmatitic veins
Where rockhounds find dumortierite
3 mapped spotsClassic worldwide localities
- Champion mine, near Oreana, Sacramento district, Humboldt Co., Nevada, once mined commercially, USA
- Clip, near Yuma, and Quartzsite, La Paz Co., Arizona, USA
- Petaca, Rio Arriba Co., New Mexico, USA
- Dehesa, San Diego Co., and from near Ogilby, Imperial Co., California, USA
- Beaunan and at Chaponost, near Lyon, Rhône, France
- Wolfshau, near Schmiedeberg, Silesia, Poland
Field-hunting tip
Where it forms: In aluminum-rich regionally metamorphosed rocks, disseminated and in veinlets cutting schists; also in pegmatitic veins. If you start seeing quartz, cordierite, kyanite in float, you are in the right ground. Typical habit: columnar, fibrous, prismatic. 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.
