Simpsonite

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Simpsonite
Simpsonite-154999.jpg
Simpsonite crystal from the Alto do Giz pegmatite, Ecuador, Brazil
General and classification
chemical formula Al 4 (Ta, Nb) 3 O 13 (OH)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DC.10 ( 8th edition : IV / D.27)
07/08/05/01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol trigonal-pyramidal 3
Space group P 3
Lattice parameters a  = 7.381  Å ; c  = 4.516 Å
Formula units Z  = 1
Physical Properties
Mohs hardness 7 to 7.5
Density (g / cm 3 ) 6.68 to 6.82
Cleavage no
Break ; Tenacity shell-like
colour colorless, white, yellow, brownish yellow
Line color White
transparency translucent
shine Diamond gloss, glass gloss, matt
Crystal optics
Refractive indices n ω  = 2.045
n ε  = 2.025
Birefringence δ = 0.020
Optical character uniaxial negative

Simpsonite is a rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the trigonal crystal system with the chemical composition Al 4 (Ta, Nb) 3 O 13 (OH) and develops mostly idiomorphic to hypidiomorphic , tabular or short prismatic crystals in centimeter size , which are either colorless or yellow to brownish-yellow in color due to foreign admixtures.


Etymology and history

The first description of Simpsonit, as part of a tantalum-rich granite - gangs ( "Tabba Tabba pegmatite") within the Pilbara - Craton , comes from the Australian mineralogist H. Bowley. The type locality is located approximately 50 km south of Port Hedland in the Australian state of Western Australia . Bowley named the mineral in honor of his colleague Edward Sydney Simpson (1875-1939), also a state-employed mineralogist who made numerous scientific contributions to the mineralogy of Western Australia. The type material is now in the Western Australian Museum in Perth .

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the simpsonite belongs to the division of "oxides with the molar ratio metal: oxygen = 1: 2 (and comparable)". Since the 9th edition of Strunz's system, this section has been more precisely subdivided according to the size of the cations involved and the crystal structure, so that the mineral can now be found in the sub-section “With medium-sized cations and layers of edge-linked octahedra”.

The systematics of minerals according to Dana also assigns simpsonite to the class of oxides. There, however, he belongs to the department of " Multiple Oxides with Niobium (Nb), Tantalum (Ta) and Titan (Ti) ".

Education and Locations

Simpsonite rarely occurs as an accessory component in tantalum-rich granitic pegmatites . Accompanying minerals include beryl , microlite , muscovite , quartz , spodumene , tantalite and various tourmalines .

So far, the mineral has been proven at 13 sites (as of 2009). In addition to the type locality in Australia, these include the Alto do Giz Pegmatite in Ecuador / Borborema in Brazil ; at the Tanco Mine near Bernice Lake , Canada ; in the Masisi Mountains of Kivu (Democratic Republic of the Congo); East Kazakhstan (Shyghys Qazaqstan); Kola in Russia; as well as Mutoko and Bikita in Zimbabwe.

Crystal structure

Simpsonite crystallizes trigonal in the space group P 3 with the lattice parameters a  = 7.381  Å and c  = 4.516 Å and one formula unit per unit cell .

See also

Individual evidence

  1. ↑ a b c Webmineral - Simpsonite (English)
  2. ↑ a b American Mineralogist Crystal Structure Database - Simpsonite (English, 1992).
  3. ↑ Mineral data sheet - Simpsonite (English, PDF 68 kB)
  4. ↑ a b Simpsonite at mindat.org (English) .
  5. ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
  6. ^ H. Bowley: Report of the Department of Mines Western Australia, for 1937 , 1938, pp. 88 and 93; Simpsonite (sp. Nov.) From Tabba Tabba, Western Australia In: Journal of the Royal Society of Western Australia , Vol. 25, 1939, pp. 89-92.
  7. ↑ Mindat - Localities for Simpsonite
  8. ↑ American Mineralogist Crystal Structure Database - Simpsonite (English, 1992).

literature

Web links

Commons : Simpsonite  - collection of pictures, videos and audio files