Dumortierite

dumortierite

cordierite

kyanite

rutile

Images
Formula: AlAl₆BSi₃O₁₈
Nesosilicate (insular SiO₄ groups), dumortierite group
Crystal System: Orthorhombic
Specific gravity: 3.21 to 3.41 measured, 3.45 calculated
Hardness: 7 to 8
Streak: White
Colour: Blue, greenish-blue, violet-blue, pale blue, pink, red
Common impurities: Fe,Ti,Mg,Ca
Environments

Pegmatites
Metamorphic environments
Hydrothermal environments

Dumortierite occurs as a constituent in pegmatitic, aplitic and granitic rocks. Also in hydrothermal deposits and regionally metamorphosed quartzites, gneisses and granulites, in Al-rich metamorphic rocks, and in high-pressure metamorphic rocks. Dumortierite may alter to muscovite-sericite and kaolinite; it may form pseudomorphs after andalusite (Dana). Associated minerals include quartz, cordierite, kyanite, andalusite, sillimanite, muscovite and rutile (HOM, Mindat).

Localities

The type locality is the Ducarre's Quarry, Beaunant, Chaponost, Lyon, Rhône, Auvergne-Rhône-Alpes, France.

At Manhattan Island, New York City, New York, USA, dumortierite has been found as specimens ranging from blue-grey to baby-blue, fibrous crystals commonly embedded in milky quartz (R&M 84.3.229).

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