10 Photos
Dumortierite
Chemical Formula	Al7BO3(SiO4)3O3 or Al6.5-7BO3(SiO4)3(O,OH)3[1]
Species	Silicates
Crystal System	Orthorhombic
Mohs Scale	7
Specific Gravity	3.3-3.4
Color	Blue, greenish-blue, Purple-blue, pale blue, red
Streak	White
Luster	Vitreous
Refractive Index	n = 1.659 - 1.678 n = 1.684 - 1.691 n = 1.686 - 1.692
Diaphaneity	Transparent to translucent
Cleavage	Distinct on , poor on ; parting on
Fracture	Fibrous
Crystal Habit：As fibrous or columnar crystals; coarsely crystalline to intimate parallel aggregates of needles; massive

Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al₇BO₃(SiO₄)₃O₃. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.

Dumortierite was first described in 1881 for an occurrence in Chaponost, in the Rh?ne-Alps of France and named for the French paleontologist Eugene Dumortier (1803-1873). It typically occurs in high temperature aluminium rich regional metamorphic rocks, those resulting from contact metamorphism and also in boron rich pegmatites. The most extensive investigation on dumortierite was done on samples from the high grade metamorphic Gfohl unit in Austria by Fuchs et al. (2005).

It is used in the manufacture of high grade porcelain. It is sometimes mistaken for sodalite and has been used as imitation lapis lazuli.

Sources of Dumortierite include Austria, Brazil, Canada, France, Italy, Madagascar, Namibia, Nevada, Norway, Poland, Russia and Sri Lanka.