This sample of Dumortierite is from Oreana, Nevada. Dumortierite has composition near to (Al,Fe)7(BO3)(SiO4)3(O,OH)3. The purple color is typical of dumortierit — Photo: Nessa Eull · CC0
Dumortierite
Also known as: Blue denim stone.
A fibrous aluminium borosilicate, usually blue to violet, used as an ornamental stone and to make high-grade porcelain.
Intro adapted from Wikipedia (CC BY-SA).
Dumortierite is an IMA-recognized mineral species in the silicate class, with the chemical formula AlAl₆BSi₃O₁₈.
It crystallizes in the orthorhombic crystal system (space group Pmcn). It is a member of the Dumortierite structural group.
Key properties: Mohs hardness 7–8.4; specific gravity 3.21–3.41; typically blue or purple or pink or brown; white streak; Vitreous to dull luster; refractive index 1.682; optically biaxial.
IMA symbol Dum, IMA status: approved, named in 1881.
Found in aluminum-rich regionally metamorphosed rocks, disseminated and in veinlets cutting schists; also in pegmatitic veins.
It is found associated with Quartz, cordierite, kyanite, andalusite, sillimanite, muscovite, rutile.
The name refers to Eugµene Dumortier (1802–1873?), French paleontologist, of Lyons, France.
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