Chemistry: Aluminum boro-silicate
Crystal system: Orthorhombic; crystals rare; usually massive fibrous or columnar aggregates.
Color: Opaque; dark blue, blue, violet, brown/red.
Hardness: 7.0 – 8.5
Cleavage: Perfect; Fracture: conchoidal.
Specific gravity: 3.26 – 3.41
Refractive index: 1.686 – 1.723 (blurred, often intergrown with quartz will give quartz reading); 0.037
Luster: Vitreous to dull.
Dispersion: -
Dichroism: Strong; brown, orange, red.
Occurrence: Metamorphic and pegmatites; Brazil, Sri Lanka, Canada, Namibia, France, Madagascar, Poland.
Notes
Ornamental material; much gem Durmortierite is intergrown with quartz; for red/brown higher physical properties; may look like lapis lazuli, sodalite and azurite; weak but variable fluorescence; usually cut cabochon, beads and carvings.
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