metamorphic
Dumortierite (or Dumortierite Quartz)
Dumortierite (Al7BO3(SiO4)3O3)
AI-generated identification · may be incorrectHardness: 7 - 8.5 (often around 7 when intergrown with quartz); Color: denim blue, dark blue to violet-blue with brown/reddish iron-stained micro-veining; Luster: vitreous to waxy/dull; Crystal system: orthorhombic; Specific gravity: 3.26 - 3.41.
- Hardness
- 7 - 8
- Luster
- vitreous to waxy/dull
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Physical properties
Hardness: 7 - 8.5 (often around 7 when intergrown with quartz); Color: denim blue, dark blue to violet-blue with brown/reddish iron-stained micro-veining; Luster: vitreous to waxy/dull; Crystal system: orthorhombic; Specific gravity: 3.26 - 3.41.
Formation & geological history
Formed in high-temperature, aluminum-rich regional metamorphic environments or boron-rich pegmatites and hydrothermally altered granitic rocks.
Uses & applications
Commonly tumbled, carved into ornamental objects, cabochons, and beads for jewelry; also historically used in manufacturing high-grade spark plugs and refractory ceramics due to high thermal resistance.
Geological facts
First described in 1881 in the Rhône-Alpes region of France and named after the French paleontologist Eugène Dumortier. It is sometimes mistaken for lapis lazuli or sodalite, but it lacks lapis lazuli's characteristic calcite patches and brassy pyrite flakes, and is substantially harder than sodalite.
Field identification & locations
Recognized by its denim or indigo blue hue, high hardness (easily scratches glass, unlike sodalite), and lack of effervescence with acid. Major sources include Brazil, Madagascar, the United States (Nevada, California), and France.
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