Metavauxite

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Metavauxite
Vauxite and Metavauxite - Llallagua, Bolivia.jpg
Vauxite and metavauxite from Llallagua, Bolivia
General and classification
chemical formula Fe 2+ Al 2 [OH | PO 4 ] 2  • 8 H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.DC.25 ( 8th edition : VII / D.09)
11/22/11/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Space group P 2 1 / c
Lattice parameters a  = 10.22  Å ; b  = 9.56 Å; c  = 6.94 Å
β  = 97.9 °
Formula units Z  = 2
Physical Properties
Mohs hardness 3
Density (g / cm 3 ) 2,345
Cleavage Please complete!
Break ; Tenacity brittle
colour colorless, white, pale green
Line color White
transparency transparent to translucent
shine Glass gloss, silk gloss
Crystal optics
Refractive indices n α  = 1.550
n β  = 1.561
n γ  = 1.577
Birefringence δ = 0.027
Optical character biaxial positive

Metavauxite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical composition Fe 2+ Al 2 [OH | PO 4 ] 2  • 8 H 2 O and develops prismatic to needle-like crystals , but also parallel to radial mineral aggregates of white or pale green color. Colorless metavauxites are also known.

Etymology and history

Metavauxite was first discovered in 1927 in the "Siglo Veinte Mine" (Llallagua Mine) near Llallagua in Bolivia and described by Samuel George Gordon (1897–1953) who also described vauxite and paravauxite as another new mineral from this site .

classification

In the old (8th edition) and new systematics of the minerals (9th edition) according to Strunz , the metavauxite belongs to the division of "water-containing phosphates with foreign anions ". Since the new Strunz mineral classification, however, this department has also been more precisely subdivided according to the size of the cations and the ratio of hydroxyl group to cation complex and the mineral is now in the subdivision “With only medium-sized cations; (OH etc.): RO 4  = 1: 1 and <2: 1 "to be found, where it forms the unnamed group" 8.DC.25 " together with ferrostrunzite , ferrostrunzite and strunzite .

The systematics used in the English-speaking world of minerals according to Dana assigns the metavauxite to the division of " hydrated phosphates etc., with hydroxyl or halogen with (AB) 4 (XO 4 ) 3 Z q  • x (H 2 O) ", where it is the only member to be found in the unnamed group “42.11.11”.

Modifications and varieties

The compound Fe 2+ Al 2 [OH | PO 4 ] 2  • 8 H 2 O is dimorphic , that is, it crystallizes as a triclinic paravauxite in addition to the monoclinic metavauxite.

Education and Locations

Metavauxite forms as a secondary mineral in the oxidation zone of tin veins. There it occurs in paragenesis with vauxite , paravauxite , wavellite and quartz .

So far, metavauxite could only be detected in its type locality , the “Siglo Veinte Mine” (Llallagua Mine) near Llallagua, only in the “Tazna Mine” near Cerro Tazna, also in the Potosí Department (status: 2009).

Crystal structure

Metavauxite crystallizes monoclinically in the space group P 2 1 / c with the lattice parameters a  = 10.22  Å ; b  = 9.56 Å; c  = 6.94 Å; β = 97.9 ° and two formula units per unit cell .

See also

Individual evidence

  1. ↑ a b c Webmineral - Metavauxite (English)
  2. ↑ a b American Mineralogist Crystal Structure Database - Metavauxite (English, 1967)
  3. ↑ a b c Metavauxite at mindat.org (engl.)
  4. ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
  5. ↑ JSTOR - Vauxite and Paravauxite, two new minerals from Llallagua, Bolivia by Samuel G. Gordon (English)
  6. ↑ Memorial of Samuel George Gordon (English, PDF 542.7 kB)
  7. ↑ American Mineralogist Crystal Structure Database - Metavauxite (English, 1967)

literature

Web links

Commons : Metavauxite  - collection of images, videos and audio files