CHEMISTRY - Al7(BO3)(SiO4)3O3
CRYSTALLOGRAPHY - Orthorhombic
CRYSTAL GROWTH AND HABITS - Usually forms fibrous crystals with poor face development. It is also commonly massive.
COLOR AND OPTICAL PROPERTIES - Dumorterite is grayish blue to greenish blue, also violet to reddish purple and brown. It is transparent to translucent.
HARDNESS - 7 - 8.5
SPECIFIC GRAVITY - 3.21 - 3.45
LUSTER - Vitreous to dull
STREAK - Very light blue
BREAKABILITY - Dumorterite has a good cleavage along {100}, poor along {110} and is brittle.
OCCURRENCE - Dumorterite is found in aluminum rich regionally metamorphosed rocks and in pegmatite veins.
ASSOCIATED MINERALS - Quartz, Cordierite, Kyanite, Andalusite, Muscovite, Sillimanite
MINERAL NAME - Dumorterite is named after Eugene Dumortier, a French paleontologist.