Dumortierite is a fibrous borosilicate mineral most recognizable by its deep, denim-like blue color. It typically forms as massive or radiating fibrous aggregates and is a popular material for cabochons and carvings due to its hardness.
Is this blue 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 blue dumortierite with a known reference. Blue 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.
- 4Match the color rangeCompare against the expected color range: blue, violet-blue, reddish-brown, green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, massive, radiating aggregates.
Often confused with
Blue Dumortierite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Blue Dumortierite is noticeably harder (Mohs 7-8.5 vs. 5.5-6).
How to tell apart: Blue Dumortierite is noticeably harder (Mohs 7-8.5 vs. 5-5.5); streak differs, so Blue Dumortierite leaves white, Lazurite leaves bright blue.
Often found alongside blue dumortierite
Minerals reported to co-occur with blue 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, radiating aggregates
- Cleavage
- Distinct on {110}
- Rarity
- Uncommon
- Uses
- Lapidary, Collector, Decorative
- Host rock
- metamorphic rocks like schist, gneiss, and pegmatites
Where rockhounds find blue dumortierite
1 mapped spotsClassic worldwide localities
- France
- USA
- Namibia
- Brazil
- Madagascar
Field-hunting tip
Where it forms: metamorphic rocks like schist, gneiss, and pegmatites. If you start seeing quartz, kyanite, andalusite in float, you are in the right ground. Typical habit: fibrous, massive, radiating aggregates. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Nevada. Start trip planning there.
Common questions
How do you identify blue dumortierite?+
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Can I find blue dumortierite in the United States?+
What rocks look like blue dumortierite?+
What minerals are found with blue dumortierite?+
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Find blue dumortierite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
