Dumortierite

Dumortierite
260px
Dumortierite from Tuléar Province (Toliara), Madagascar
General
Category Nesosilicate
Formula
(repeating unit)		 Al7BO3(SiO4)3O3 or Al6.5-7BO3(SiO4)3(O,OH)3[1]
Strunz classification 9.AJ.10
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Unit cell a = 11.77 Å, b = 20.21 Å
c = 4.71 Å; Z = 4
Identification
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
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 [1][2][3]

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 Rhône-Alps of France and named for the French paleontologist Eugène Dumortier (1803–1873).[4] 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, Peru, Poland, Russia and Sri Lanka.

See also

References

  1. 1 2 http://webmineral.com/data/Dumortierite.shtml Webmineral data
  2. ↑ http://rruff.geo.arizona.edu/doclib/hom/dumortierite.pdf Handbook of Mineralogy
  3. ↑ http://www.mindat.org/min-1329.html Mindat.org
  4. ↑ Wikisource "Dumortierite". Encyclopædia Britannica. 8 (11th ed.). 1911. p. 667.
  • 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. 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; M. H. Hey (1958). "New Data for Dumortierite". Neues Jahrbuch für Mineralogie. 31 (242): 901–907. doi:10.1180/minmag.1958.031.242.02.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.