Brazilianite

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Brazilianite
Brasilianite - Minas Gerais, Brazil.jpg
Brazilianite crystal from Galilea, Minas Gerais, Brazil
General and classification
chemical formula NaAl 3 [(OH) 2 | PO 4 ] 2
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BK.05 ( 8th edition : VII / B.12)
05.41.07.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Space group P 2 1 / n
Lattice parameters a  = 11.233  Å ; b  = 10.142 Å; c  = 7.097 Å
β  = 97.37 °
Formula units Z  = 4
Physical Properties
Mohs hardness 5.5
Density (g / cm 3 ) 2.98
Cleavage good after {010}
Break ; Tenacity uneven to scalloped
colour colorless, white, yellowish, greenish-yellow
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.602
n β  = 1.609
n γ  = 1.621 to 1.623
Birefringence δ = 0.019 to 0.021
Optical character biaxial positive
Axis angle 2V = 71 to 75 °

Brazilite is a rather rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical composition NaAl 3 [(OH) 2 | PO 4 ] 2 and develops mostly transparent to translucent, short prismatic or isometric crystals , but also radial, grainy or massive aggregates .

Etymology and history

For the first time scientifically described and recognized as an independent mineral, the Brazilianite was in 1945 by Pough and Henderson. The type locality is Conselheiro Pena near Minas Gerais in Brazil and the mineral was named after this location (Brazil). The Brazilianite was known before, but was mistaken for chrysoberyl .

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the Brazilianite belongs to the department of "Anhydrous phosphates with foreign anions ". The new Strunz'sche mineral classification, however, subdivides here more precisely according to the size of the cations involved and the molar ratio between foreign anions and phosphate complex . The mineral is now in the subsection "With medium-sized and large cations and the molar ratio (OH, etc.): RO4 = 2: 1 or 2.5: 1".

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Brazilianite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here it can be found in the unnamed group 41.05.07 within the subsection “Anhydrous phosphates etc., with hydroxyl or halogen with (AB) 2 (XO 4 ) Z q ”.

Crystal structure

Brazilianite crystallizes monoclinically in the space group P 2 1 / n with the lattice parameters a  = 11.233  Å ; b  = 10.142 Å; c  = 7.097 Å and β = 97.37 ° as well as four formula units per unit cell .

properties

Pure Brazilianite is colorless or white. However, it can be yellowish to greenish-yellow in color due to foreign admixtures.

Boric acid and borax etch the mineral, hydrofluoric acid destroys it.

Education and Locations

Brazilianite is formed from hydrothermal solutions in phosphate-rich zones of granite - pegmatites , but can also arise metamorphically in sedimentary rocks . It occurs in paragenesis with various minerals, including albite , amblygonite , apatites , agelite , bertossaite , muscovite , quartz , tourmaline group minerals and whitlockite .

So far, Brazilianite has been found at 45 sites (status: 2009): Salta in Argentina; East Gippsland Shire in Australia; Paraíba and Rio Grande do Norte in the northeast region, Espírito Santo and Minas Gerais in the southeast region of Brazil; Waidhaus in Germany; Ébreuil in France; at Dawson in Canada; Karibib in Namibia; Spittal an der Drau in Austria; Gatumba in Rwanda ; Zamora in Spain; Richtersveld in South Africa; Moravia in the Czech Republic; and in the US regions of Arizona , Connecticut , Maine , New Hampshire, and South Dakota .

use

As a gem

Brazilite is only processed into gemstones , but is not yet very widespread as a relatively new jewelry mineral. Since the stone has only about the hardness of glass , it is sensitive to the stresses and strains of jewelry making and wear and can easily be damaged as arm or finger jewelry in everyday use. Due to its color, there is a risk of confusion with amblygonite, apatite, chrysoberyl, beryl and topaz , among others .

See also

literature

Web links

Commons : Brazilianite  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Handbook of Mineralogy - Brazilianite (mineral data sheet, English, PDF 64.4 kB)
  2. ↑ a b American Mineralogist Crystal Structure Database - Brazilianite (English, 1974)
  3. ↑ a b c Brazilianite at mindat.org (English)
  4. ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
  5. ↑ Annals of the Natural History Museum Vienna 197 - From the new acquisitions of the Mineralogical-Petrographic Department - Brasilianite and Petalit from Minas Gérais, Brazil (PDF file; 1.01 MB)
  6. ↑ American Mineralogist Crystal Structure Database - Brazilianite (English, 1974)
  7. ^ A b Gem etiquette by Prof. Leopold Rössler - Brasilianit
  8. ↑ Mindat - Localities for Brasilianite (English)
  9. ^ Walter Schumann: Precious stones and gemstones . 13th edition. BLV Verlags GmbH, 2002, ISBN 3-405-16332-3 , p. 206 .