Dumortierite
Aluminium boro-silicate, Al7(BO3)(SiO4)3O3
A hard aluminum borosilicate famous for its rich denim-blue color, often forming dense fibrous masses or coloring quartz blue.
- Mohs hardness
- 7-8.5
- Color
- Deep blue to violet-blue, sometimes pink or brown
- Type
- mineral
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Overview
Dumortierite is an aluminium borosilicate mineral best known for its intense blue to violet color, frequently compared to faded denim or sodalite. It was named after the French paleontologist Eugene Dumortier.
It typically occurs as fibrous or columnar masses rather than well-formed crystals. When fine fibers permeate quartz, the result is sold as dumortierite quartz, a popular durable lapidary material.
The color comes from trace iron and titanium. Massive material is opaque to translucent, while the rare crystals can be transparent.
Formation & geology
Dumortierite forms in aluminum-rich metamorphic rocks, especially those altered by boron-bearing fluids during high-temperature, contact, or regional metamorphism. It is also found in some pegmatites and aluminous schists and gneisses.
It commonly grows alongside quartz, sillimanite, andalusite, and other aluminosilicates in environments where alumina is abundant.
Significant deposits occur in Brazil, Madagascar, Namibia, France, Norway, Sri Lanka, Canada, and the United States (notably Nevada, California, and Arizona).
How to identify it
Key clues are a denim-blue to violet color combined with high hardness: 7 to 8.5, hard enough to scratch glass and quartz easily. The streak is white to pale blue.
Massive dumortierite shows a fibrous or radiating texture and a silky to dull luster. It may display pleochroism, appearing blue, violet, or reddish-brown from different angles.
Look-alikes: Sodalite and lapis lazuli are softer (around 5.5-6) and lapis often shows pyrite flecks. Lazulite and azurite are also softer. The combination of strong blue color with quartz-beating hardness is the best distinguishing trait.
Uses & significance
Dumortierite and dumortierite quartz are cut into cabochons, beads, and tumbled stones, valued for a deep blue that mimics lapis or sodalite but with greater durability. It is occasionally faceted when transparent.
Industrially, dumortierite is used in the manufacture of high-grade porcelain and ceramics, where its alumina content aids in producing heat-resistant, high-strength bodies (for example in spark plugs and refractory ware).
In metaphysical circles it is associated with mental clarity, focus, and communication, though these are spiritual rather than verified properties.
Frequently asked questions
Is dumortierite the same as sodalite?
No. Both are blue, but dumortierite is a much harder borosilicate (7-8.5) while sodalite is a softer feldspathoid (5.5-6). Dumortierite will scratch glass cleanly.
What is dumortierite quartz?
It is quartz shot through with fine blue dumortierite fibers, giving the stone a blue color while keeping quartz's durability; it is a common lapidary material.
Is dumortierite rare?
Massive blue dumortierite is reasonably available, but transparent, gem-quality crystals are quite rare and collectible.
Can dumortierite be used in jewelry?
Yes. Its high hardness makes it durable enough for rings, pendants, and beads, usually as cabochons or tumbled stones.
Dumortierite guides
In-depth guides for identifying, valuing, and understanding Dumortierite.
Dumortierite identified by the community
Real specimens identified with Rock Identifier.
