Vanadinite

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Vanadinite
Maroc - Vanadinite.jpg
Vanadinite (orange) and pyrolusite (gray).
General and classification
chemical formula Pb 5 [Cl | (VO 4 ) 3 ]
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates - anhydrous phosphates with foreign anions
System no. to Strunz
and to Dana 		8.BN.05 ( 8th edition : VII / B.39)
08.41.04.03
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol hexagonal dipyramidal; 6 / m
Space group P 6 3 / m
Lattice parameters a  = 10.331  Å ; c  = 7.343 Å
Formula units Z  = 2
Frequent crystal faces {0001}, {10 1 0}, {10 1 1}, {21 3 1}
Physical Properties
Mohs hardness 3
Density (g / cm 3 ) 6.8 to 7.1
Cleavage no
Break ; Tenacity shell-like, uneven
colour yellow, orange, brown, rarely red
Line color white to pale yellow and pale brownish yellow
transparency transparent, translucent to opaque
shine Diamond luster
Crystal optics
Refractive indices n ω  = 2.416
n ε  = 2.350
Birefringence δ = 0.066
Optical character uniaxial negative
Pleochroism weak

Vanadinite is a rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the hexagonal crystal system with the chemical composition Pb 5 [Cl | (VO 4 ) 3 ] and develops short to long prismatic (rarely also pyramidal) crystals , but also grape to earthy or radial aggregates in white, gray, yellow, orange to brown color.

Vanadinite is a member of the apatite - pyromorphite group .

Etymology and history

Vanadinite was first found and described in 1838 in Zimapan , Mexico . It was named with reference to its vanadium content.

classification

In the Strunz system , vanadinite is assigned to phosphates, arsenates and vanadates with additional anions but without crystal water . In both the eighth edition and the ninth edition, it belongs to the apatite group with apatite , pyromorphite and other minerals. In the 9th edition, this is also a subgroup of phosphates, arsenates and vanadates with only large cations (OH etc.) and a ratio of anions and RO 4 of 0.33: 1.

In the systematics of minerals according to Dana it forms with pyromorphite, mimetite and pyromorphite a subgroup of the anhydrous phosphates etc. with hydroxide or halogen ions and the composition (A) 5 (XO 4 ) 3 Z q . These three minerals at least partially form a mixed crystal system with each other, in which (VO 4 ) 3− is substituted by (PO 4 ) 3− to pyromorphite or (AsO 4 ) 3− to mimetite.

Crystal structure

Structure of vanadinite, __ Pb 2+   __ V 5+ __ O 2− , __ Cl -

Vanadinite crystallizes hexagonally in the space group P 6 3 / m (crystal class 6 / m ) with two formula units per unit cell and the lattice constants a  = 10.331 Å and c  = 7.343 Å. Vanadium is surrounded by oxygen in a tetrahedral manner. The chloride anions are located on the corners of the unit cell and on the cell edges at c / 2. Lead occupies two differently coordinated grid positions.

properties

With a Mohs hardness of 3, vanadinite is one of the soft minerals. It melts easily in front of the soldering tube and dissolves well in nitric acid .

Modifications and varieties

Endlichit on Descloizit (black) from Touissit , Morocco

As Endlichit or arsenic Vanadinit one by small additions of is arsenic yellow-colored variety of Vanadinit referred. Endlichit was described in 1885 by Friedrich August Genth (1820–1893) and Gerhard vom Rath (1830–1888).

Education and Locations

Vanadinit is a secondary mineral and forms in accompaniment of Anglesit , barite , calcite , Cerussit , Mottramit , Pyromorphit , Wulfenit and goethite in lead - deposits . Occasionally it is found in an oriented fashion with pyromorphite or mimetite or ingrown with descloicite .

In addition to its type locality, it was found in Mexico, among others, in Argentina , the Black Forest in Germany , Djebel Mahseur and Mibladen in Morocco , Tsumeb in Namibia , Wanlockhead in Scotland , Gotland in Sweden , Berezovsk in Siberia , and Arizona in the USA .

use

Vanadinite is used as a raw material to extract the alloying element vanadium, which is important for special steels .

Vanadinite cannot be used as a gemstone due to its low hardness. Occasionally it is cut into a cabochon shape by collectors .

Vanadinite is also used as a pigment . When the mineral is ground , a yellow powder results, with which, when rubbed in binder , intensely yellow to orange layers of color can be produced. The pigment was used almost exclusively in China, especially in the area around Xi'an , for example on the soldiers of the terracotta army of Emperor Qin Shihuangdi . Outside of China, vanadinite was only found as a pigment on a Hellenistic stele from Alexandria , which is now in the Louvre .

See also

literature

  • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology. 7th, completely revised and updated edition. Springer, Berlin et al. 2005, ISBN 3-540-23812-3 .
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals. Edition Dörfler in Nebel-Verlag, Eggolsheim 2002, ISBN 3-89555-076-0 .
  • Catharina Blänsdorf: Studies on the coloring of figures from the terracotta army and from other burial pits in the grave complex of the First Chinese Emperor Qin Shihuangdi, Siegl, Munich, 2015: 255–262.

Web links

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

Individual evidence

  1. ↑ a b c J. Trotter, WH Barnes: The structure of vanadinite. (PDF; 656 kB), In: The Canadian Mineralogist. 6, 1958, pp. 161-173.
  2. ↑ Stefan Weiß: The large Lapis mineral directory. 4th edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6 .
  3. ^ List of minerals according to Dana at webmineral.com .
  4. ↑ Yongshan Dai, John M. Hughes: Crystal Structure Refinement of Vanadinite and Pyromorphite. In: Canadian Mineralogist. Vol. 27, 1989, pp. 189-192. (PDF; 383 kB).
  5. ^ Paul Ramdohr , Hugo Strunz : Textbook of Mineralogy. 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 .
  6. ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th, through and exp. Edition. German publishing house for basic industry (VEB), Leipzig 1979, ISBN 3-342-00288-3 , p. 644 .
  7. ↑ WM Myers, S. Zerfoss: Frederick Augustus Genth. 1820-1893. Chemist - Mineralogist - Collector. The Pennsylvania State College, 1946. ( PDF 1.13 MB, p. 14. ( Memento of March 4, 2012 in the Internet Archive ))
  8. ↑ Mineral data sheet - Vanadinite (English, PDF 62.4 kB)
  9. ^ Walter Schumann: Precious stones and gemstones. 13th edition. BLV, Munich 2002, ISBN 3-405-16332-3 .
  10. ↑ Catharina Blänsdorf: Studies on the color version of figures from the terracotta army and from other burial pits in the grave complex of the First Chinese Emperor Qin Shihuangdi . Siegl, Munich 2015, p. 255-262 .