Variscit
| Variscit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Al [PO 4 ] • 2H 2 O |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8th CD.10 ( 8th edition : VII / C.09) 04/40/01/01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group | Pcab (No. 61, position 2) |
| Lattice parameters | a = 9.82 Å ; b = 9.63 Å; c = 8.56 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 4.5 |
| Density (g / cm 3 ) | measured: 2.57 to 2.61; calculated: 2.59 |
| Cleavage | good after {010}; indistinct after {001} |
| Break ; Tenacity | uneven to mussel-like, splintery |
| colour | colorless, greenish, blue-green, rarely red |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss to wax gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.563 n β = 1.588 n γ = 1.594 |
| Birefringence | δ = 0.031 |
| Optical character | biaxial negative |
| Axis angle | 2V = 50 ° |
Variscit (also Variscite ) is a mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the orthorhombic crystal system with the chemical composition Al [PO 4 ] · 2H 2 O, so it is chemically a water-containing aluminum orthophosphate . With the hydrous iron (III) phosphate Strengit , which also crystallizes orthorhombically , Variscit forms a seamless series of mixed crystals .
Variscite occurs predominantly in the form of bulbous, grape or massive mineral aggregates and crusty coatings; it rarely forms isometric, pseudo-octahedral crystals up to about 1.5 mm in size. In its pure form, the mineral is transparent and colorless. However, it can also have a greenish, blue-green and rarely also red color and a brown matrix interspersed with foreign admixtures, whereby the transparency decreases accordingly. However, the line color is always white. With a Mohs hardness of 4.5, Variscite is still one of the soft minerals that can be easily scratched with a knife.
Etymology and history
The name of the mineral is derived from Variscia , the Latin name of the Vogtland , where it was first described in 1837 by the German mineralogist August Breithaupt . Breithaupt named it two years earlier when he wrote:
“ The mineral from Mosbach in Voigtlande, not the one from Oelsnitz which was issued for Kalait, is now called variscite after I recognized it as a special species. Also contains phosphoric acid. "
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the variscite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates without foreign anions ", where it belongs together with Kolbeckite , Koninckit , Malhmoodit , Mansfieldit , metavariscite , Paraskorodit , Phosphosiderit , scorodite , Strengit and Yanomamit formed a distinct group.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns variscite to the class of “phosphates, arsenates and vanadates” and there to the department of “phosphates etc. without additional anions ; with H 2 O “. However, this section is further subdivided according to the size of the cations involved and the molar ratio of phosphate, arsenate or vanadate complex to the water of crystallization contained , so that the mineral is classified in the sub-section “With only medium-sized cations; RO 4 : H 2 O = 1: 2 "can be found where, together with Mansfieldite, Redondite , Skorodite, Strengite and Yanomamite, the" Variscite group "named after him with the system no. 8.CD.10 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking area , assigns the variscite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he is also the namesake of the "Variscit group" with the system no. 40.04.01 and the other members Strengit, Skorodit, Mansfieldit and Yanomamit can be found within the subdivision of " Water-containing phosphates etc., with A 3+ XO 4 × x (H 2 O) ".
Crystal structure
Variscite crystallizes orthorhombically in the space group Pcab (space group no. 61, position 2) with the lattice parameters a = 9.82 Å ; b = 9.63 Å and c = 8.56 Å and 8 formula units per unit cell .
Modifications and varieties
The compound Al [PO 4 ] · 2H 2 O is dimorphic and occurs naturally as a monoclinic metavariscite in addition to the orthorhombic variscite . The anhydrous aluminum orthophosphate can be found in nature as the mineral berlinite .
As Amatrix (also American matrix or Variscitquarz ) is a variety called the Variscit that direction as quartz is grown.
Education and Locations
As a secondary mineral, variscite is formed by direct deposition when phosphate-containing surface waters react with rocks that have a high aluminum content. The mineral is often there with white to yellow veins of Crandallit crossed, but also comes with carbonate-fluorapatite , Gordonit , Goyazit , Kolbeckit , Millisit , Montgomeryit , Overit and Wardit socialized before.
So far (as of 2011), Variscit has been found at around 240 sites. In addition to its type locality Vogtland, the mineral occurred in Germany in the Fichtel Mountains and the Upper Palatinate in Bavaria; in the Odenwald and near Wetzlar in Hessen; in the Sauerland in North Rhine-Westphalia; near Chemnitz , in the Ore Mountains and Upper Lusatia in Saxony and near Gera and Zeulenroda in Thuringia.
In Austria, Variscit was found near Mühldorf in Lower Austria and near Frohnleiten and Leoben in Styria.
The Clay Canyon near Fairfield in the US state of Utah , where greenish tubers up to 30 cm in diameter were found, is worth mentioning due to the extraordinary variscite finds.
Other locations are Argentina , Brazil , Australia , Belgium , Bolivia , Brazil, Bulgaria , Cape Verde , China , the Democratic Republic of the Congo , France , Iran , Ireland , Italy , Japan , Canada , Kazakhstan , Kyrgyzstan , Colombia , Malaysia , Mexico , Mozambique , Namibia , Poland , Portugal , Rwanda , Romania , Russia , Sweden , Senegal , Slovakia , Spain South Africa , Czech Republic , Hungary , Uruguay , Uzbekistan , Venezuela , the United Kingdom (Great Britain) and the United States .
Variscite has also been detected in rock samples from the Pacific Ocean , more precisely near Clipperton Island .
Use as a gem stone
Despite its relatively low hardness and brittleness, variscite is often processed into gemstones due to its often lively play of colors , especially since it can look very similar to other valuable gemstones such as chrysocolla , jade and turquoise . If variscite is permeated with brown to black veins (matrix), it can also be confused with the coveted matrix turquoise.
Variscite is processed into either cabochons or layer stones and is occasionally sold under the misleading trade names "Australian Turquoise", "California Turquoise", "Nevada Turquoise", "Utah Turquoise" or "Utalith".
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 641 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 174 .
- ES Larsen: The Mineralogy and Paragenesis of the Variscite Nodules from near Fairfield, Utah. In: American Mineralogist 27, 1942, pp. 441-451.
- R. Kniep et al: Variscite. In: Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry 33, 1977, pp. 263-265.
- J. Garcia-Guinea et al .: Radiation damage of variscite in historic crafts: Solarization, decolouration, structural changes and spectra from ionoluminescence. In: Radiation Physics and Chemistry 77, 2008, pp. 18-22.
Web links
- Webmineral data (English)
- Variscit
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 477 .
- ↑ Webmineral - Variscite (English)
- ↑ Variscite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.4 kB , English)
- ↑ a b c d Mindat - Variscite (English)
- ↑ A. Breithaupt: Determination of new minerals. (PDF; 919 kB) In: Journal for practical chemistry 10, 1837, pp. 501-512.
- ^ A. Breithaupt: Letter of August 4, 1835 [about Marmolith, Gediegen Irid, Variszit] In: New Yearbook for Mineralogy, Geognosy, Geology and Petrefactenkunde pp. 524-526.
- ^ Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags GmbH, Munich et al. 2002, ISBN 3-405-16332-3 , p. 212 .
- ↑ a b List of localities for Variscite at [Mineralienatlas] and at Mindat
- ↑ Bernhard brother embellished stones . Neue Erde Verlag, 2005, ISBN 3-89060-025-5 .
- ^ Precious stone etiquette from Prof. Leopold Rössler - Variscit