Villiaumite

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Villiaumite
Villiaumite-229832.jpg
Orange colored villiaumite crystals from the Aris quarries near Windhoek , Namibia ( total size : 9 cm × 5.4 cm × 5 cm)
General and classification
chemical formula NaF
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.AA.20 ( 8th edition : III / A.02)
01/09/01/03
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fm 3 m (No. 225)Template: room group / 225
Lattice parameters a  = 4.63  Å
Formula units Z  = 4
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 2.79; calculated: 2.808
Cleavage completely after {001}
Break ; Tenacity brittle
colour dark red, carmine, orange brown, lavender pink; synthetic colorless
Line color pale red to white
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive index n  = 1.327 to 1.328
Birefringence none, since optically isotropic; abnormal birefringence possible
Optical character abnormal biaxial negative
Other properties
Chemical behavior easily soluble in water
Special features fluorescent, very toxic

Villiaumite is a rarely occurring mineral from the mineral class of " halides " with the chemical composition NaF and is therefore chemically sodium fluoride .

Villiaumit crystallizes in the cubic crystal system , but it is rarely visible to the naked eye crystals , which then but can reach up to 15 cm in size. The mineral is usually found in the form of granular to massive mineral aggregates . The surfaces of the transparent to translucent crystals show a glass-like sheen . Due to foreign admixtures or the effects of ionizing radiation of radioactive substances, Villiaumit can take on a dark red to carmine red, orange-brown or lavender-pink color. The line color , on the other hand, is pale red to white.

Etymology and history

The mineral was discovered in the sample collection Maxime Villiaume, an officer of the colonial artillery corps stationed in northern Madagascar , who helped to acquire mineral and rock collections in Madagascar and Guinea .

Antoine Lacroix found the previously unknown mineral on one of the samples from the island of Roume in Guinea , which is part of the Îles de Los . He published his analysis results and scientific description in 1908 in the Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences de Paris and named the mineral Villiaumite in honor of its discoverer.

The type material (cotype) of the mineral is in the Muséum national d'histoire naturelle (Sigel MNHN or English MHN) under catalog no. 108.220 / 6 kept.

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the villiaumite belonged to the mineral class of the "halides" and there to the division of the "simple halides", where together with bromargyrite , carobbiite , chlorargyrite , halite and sylvine it belongs to the "halite Series "with the system no. III / A.02 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies the villiaumite in the somewhat more refined section of "simple halides without H 2 O". This is further subdivided according to the molar ratio of metal (M) to halogen (X), so that the mineral can be found according to its composition in the sub-section "M: X = 1: 1 and 2: 3", where it can be found together with Carobbiit, Griceit , Halit, Sylvin the "Halitgruppe" with the system no. 3.AA.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the villiaumite to the class and division of the same name of "halides". Here he is also in the "Halite group" with the system no. 01/09/01 to be found in the subsection " Anhydrous and hydrous halides with the formula AX ".

Crystal structure

Structure of villiaumite

Villiaumite crystallizes in the cubic crystal system in the space group Fm 3 m (space group no. 225) with the lattice parameter a = 4.634  Å and four formula units per unit cell . Template: room group / 225

The crystal structure of Villiaumit similar to the structure of sodium chloride , except that fluorine - ions , the lattice sites of the chlorine occupy ions.

properties

Synthetic villiaumite (sodium fluoride) is colorless and transparent. Natural Villiaumite can also be discolored by heating it to 300 ° C.

Villiaumit is water-soluble and forms a colorless solution. If it comes into contact with acids, toxic hydrogen fluoride is formed .

Under UV light the mineral shows a dark red or orange to yellow fluorescence .

Education and Locations

A bright red Villiaumite crystal in the bedrock

Villiaumit formed in nepheline - syenites by reaction of nepheline, Aegirin and fluorine to Villiaumit, albite , magnetite and oxygen . In contrast, quartz prevents the formation of villiaumite. It is also rarely found in dry salt lakes .

As a rare mineral formation, Villiaumite is only known from a few sites or a few samples, with around 40 sites being documented so far.

Besides its type locality Rouma the mineral was found on the nearby and also to the archipelago de Iles lot belonging Kassa Island . Other African sites are the Magadisee , a lake of soda in the Magadi-Natron-Basin in Kajiado County , Kenya ; the Aris quarries near the town of the same name in the Namibian municipality of Windhoek and the Ol Doinyo Lengai volcano in the Arusha area of ​​Tanzania.

Other well-known sites include Poços de Caldas in the Brazilian state of Minas Gerais , the Poudrette quarry on Mont Saint-Hilaire and the Demix-Varennes quarry in the municipality of Marguerite-D'Youville (formerly Lajemmerais ) in the province of Québec and the alkali deposit Nechalacho in the syenite complex of Thor Lake in the Mackenzie district in Canada, the Kvanefjeld uranium deposit in the Ilimaussaq intrusion near Narsaq (Kujalleq municipality) in Greenland (Denmark), the carbonatites in the Fen complex near the village of Nome in the Norwegian province of Telemark, several sites in the Chibinen (Koaschwa, Kukiswumtschorr, Raswumtschorr) and the Lowosero-Tundra ( Alluaiw , Karnasurt, Kedykverpakhk) in Russia as well as the Porphry Mountain near Jamestown in Colorado and the quarry Point of Rocks near Springer in New Mexico in the United States of America .

use

Due to its rarity, villiaumite is of no importance as a raw material, even if the sodium fluoride compound has numerous uses. However, this is easier to produce synthetically.

Despite its toxicity, the rare mineral is a sought-after collector's mineral due to its appealing color, which is occasionally even offered in various faceted gemstone cuts .

Precautions

Due to its toxicity , mineral samples from Villiaumit should only be kept in dust-tight containers. Absorption into the body ( incorporation , ingestion ) should also be prevented in any case and, for safety, direct body contact should be avoided and face masks and gloves should be worn when handling the mineral

See also

literature

  • A. Lacroix: Sur l'existance du fluorure de sodium crystallisé comme élément des syénites néphéliniques des Îles de Los . In: Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences de Paris . tape 146 , 1908, pp. 213–216 (French, abstract from gallica.bnf.fr [accessed November 28, 2018]).

Web links

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

Individual evidence

  1. ^ A b c Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  150 .
  2. ↑ a b c d e f g Villiaumite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 60  kB ; accessed on November 28, 2018]).
  3. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  4. ↑ Mindat - Villiaumite (English)
  5. ^ A. Lacroix: Sur l'existance du fluorure de sodium cristallisé comme élément des syénites néphéliniques des Îles de Los . In: Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences de Paris . tape 146 , 1908, pp. 213–216 (French, abstract from gallica.bnf.fr [accessed November 28, 2018]).
  6. ↑ Catalog of Type Mineral Specimens - V. (PDF 40 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, p. 5 , accessed August 29, 2019 .
  7. ↑ Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason , Abraham Rosenzweig: Dana's New Mineralogy . 8th edition. John Wiley & Sons, New York (et al.) 1997, ISBN 0-471-19310-0 , pp. 375-376 .
  8. ^ JC Stormer, Jr., ISE Carmichael: Villiaumite and the occurrence of fluoride minerals in igneous rocks . In: American Mineralogist . tape 55 , 1970, pp. 126–134 (English, minsocam.org [PDF; 531 kB ; accessed on November 28, 2018]).
  9. ↑ Mindat - Number of localities for Villiaumit
  10. ↑ Find location list for Villiaumite in the Mineralienatlas and in Mindat
  11. ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 238 .
  12. ↑ Edelsteinlabor Dieter Pschichholz: Gemstones for lovers (PDF 8409 kB; p. 31)