Dumortierite

Dumortierite is a natural aluminium borosilicate mineral that usually occurs as massive, fibrous or granular material in blue, violet-blue, pink or reddish brown. Massive blue and violet dumortierite is cut into cabochons and beads, while transparent faceted stones are very rare. It is a distinct mineral and should not be confused with dumortierite quartz, quartz rock coloured by dumortierite.

Products made with this material

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Dumortierite
Dumortierite

4mm / 6mm / 8mm / 10mm

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Full material guide
Material facts

What the material is, where it comes from or how it is made, identification and care, from the cited sources.

Properties

Nature Natural mineral
Chemical formula Al(Al₂O)(Al₂O)₂(SiO₄)₃(BO₃)
Color Blue, greenish blue, violet-blue, pale blue, pink, red; also brown
Crystal system Orthorhombic; crystals rare, usually massive, fibrous or granular
Mohs hardness 7 to 8 (crystals up to 8.5; massive material about 7)
Specific gravity 3.21 to 3.41
Refractive index 1.659 to 1.692
Birefringence 0.014 to 0.027
Pleochroism Strong (deep blue or violet / yellow to red-violet or nearly colourless / colourless or very pale blue)
Luster Vitreous to dull

Origins & sources

Dumortierite forms in aluminium-rich regionally metamorphosed rocks, disseminated or in veinlets cutting schist, and in pegmatitic veins. Its type locality is a quarry at Beaunant near Lyon, France. The International Gem Society lists violet gem material from Pershing County, Nevada, material from Arizona, France and Madagascar, facetable bluish-green material from Minas Gerais, Brazil, and transparent reddish-brown stones from Sri Lanka.

Identification

Dumortierite is notably hard for an opaque blue stone (7 to 8) and shows strong pleochroism in blue and violet tones. The International Gem Society notes that Arizona "dumortierite" is actually a quartz-impregnated variety, so blue quartz-rich material sold under this name may be dumortierite quartz rather than the pure mineral. Fibrous inclusions have been noted in transparent Brazilian stones.

Care

Not collected yet

History & culture

History

Dumortierite is named in honour of Eugène Dumortier (1801–1876), a palaeontologist from Lyon, France, who wrote on the Jurassic deposits of the Rhône basin; the mineral's type locality is near Lyon.

Cultural meanings

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Traditional beliefs

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Sources

Collected Oct 23, 2026