Properties
| Category | Nesosilicate |
|---|---|
| Formula | Al7BO3(SiO4)3O3 or Al6.5-7BO3(SiO4)3(O,OH)3 |
| Crystal system | Orthorhombic |
| Color | Blue, greenish-blue, violet-blue, pale blue, red |
| Crystal habit | As fibrous or columnar crystals; coarsely crystalline to intimate parallel aggregates of needles; massive |
| Cleavage | Distinct on {100}, poor on {110}; parting on {001} |
| Fracture | Fibrous |
| Mohs scale hardness | 7–8.5 |
| Luster | Vitreous to dull |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.3–3.4 |
From the Wikipedia article
Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al7BO3(SiO4)3O3. It crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium results in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored crystal containing abundant dumortierite inclusions. Although sometimes called a quartz, Dumortierite is not truly a quartz.
Source
Source record: crystal-compendium/dumortierite/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Dumortierite — revision id 1371559996. Text and properties from Wikipedia, licensed CC BY-SA 4.0.