Dumortierite
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 | |
|---|---|
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] |
| IMA symbol | Dum[2] |
| Strunz classification | 9.AJ.10 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pmcn (no. 62) |
| 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][3][4] |
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).[5] 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
- ^ a b http://webmineral.com/data/Dumortierite.shtml Webmineral data
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ http://rruff.geo.arizona.edu/doclib/hom/dumortierite.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-1329.html Mindat.org
- ^ . Encyclopædia Britannica. Vol. 8 (11th ed.). 1911. p. 667.
- 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. Bibcode:1971MinM...38..526S. doi:10.1180/minmag.1971.038.296.19. S2CID 54878132.
- 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". Mineralogical Magazine and Journal of the Mineralogical Society. 31 (242): 901–907. Bibcode:1958MinM...31..901C. doi:10.1180/minmag.1958.031.242.02.