- Dumortierite
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Dumortierite General Category Boro-silicate mineral Chemical formula Al7BO3(SiO4)3O3 or Al6.5-7BO3(SiO4)3(O,OH)3[1] Crystal symmetry Orthorhombic 2/m 2/m 2/m Unit cell a = 11.77 Å, b = 20.21 Å,
c = 4.71 Å; Z=4Identification Color Blue, greenish-blue, violet-blue, pale blue, red Crystal habit As fibrous or columnar crystals; coarsely crystalline to intimate parallel aggregates of needles; massive Crystal system Orthorhombic - Dipyramidal Twinning Common on {110}, may produce trillings Cleavage Distinct on {100}, poor on {110}; parting on {001} Fracture Fibrous Mohs scale hardness 7 - 8.5 Luster Vitreous to dull Streak White Diaphaneity Transparent to translucent Specific gravity 3.3 - 3.4 Optical properties Biaxial (-) Refractive index nα = 1.659 - 1.678 nβ = 1.684 - 1.691 nγ = 1.686 - 1.692 Birefringence δ = 0.027 Pleochroism Strong; X = deep blue or violet; Y = yellow to red-violet or nearly colorless; Z = colorless or very pale blue 2V angle Measured: 20° to 52°, Calculated: 30° Dispersion r > v; strong References [2][3][1] 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 from Alpine County, California, USA, possibly pseudomorphic after tourmaline (size: 5.7 x 2.7 x 1.1 cm)
Dumortierite was first described in 1881 for an occurrence in Chaponost, in the Rhône-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.
See also
References
- ^ a b http://webmineral.com/data/Dumortierite.shtml Webmineral data
- ^ http://rruff.geo.arizona.edu/doclib/hom/dumortierite.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-1329.html Mindat.org
- Mineral galleries
- DUMORTIERITE AS A COMMERCIAL MINERAL
- DUMORTIERITE FROM NEVADA
- Y. Fuchs, A. Ertl, J.M. Hughes, S. Prowatke, F. Brandstätter & R. Schuster (2005). "Dumortierite from the Gföhl unit, Lower Austria". European Journal of Mineralogy 17 (1): 173–183. doi:10.1127/0935-1221/2005/0017-0173. http://eurjmin.geoscienceworld.org/cgi/content/abstract/17/1/173. Retrieved 2008-12-11.
- M. Sabzehei (1971). "Dumortierite from Iran: A First Record". Mineralogical Magazine 38 (296): 526–527. doi:10.1180/minmag.1971.038.296.19.
- PB Moore, T Araki (1978). "Dumortierite A detailed structure analysis". Neues Jahrbuch für Mineralogie.
- G. F. Claringbull and M. H. Hey (1958). "New Data for Dumortierite". Neues Jahrbuch für Mineralogie 31 (242): 901–907. doi:10.1180/minmag.1958.031.242.02.
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