Gonnardite
| Gonnardite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (Na, Ca) 2 [(Si, Al) 5 O 10 ] • 3H 2 O |
|
Mineral class (and possibly department) |
Silicates and Germanates - framework silicates (tectosilicates) |
|
System no. to Strunz and to Dana |
9.GA.05 ( 8th edition : VIII / J.21) 77.01.05.07 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | tetragonal-scalenohedral; 4 2 m |
| Space group | I 4 2 d (No. 122) |
| Lattice parameters | a = 13.21 Å ; c = 6.62 Å |
| Formula units | Z = 1 |
| Physical Properties | |
| Mohs hardness | 5 |
| Density (g / cm 3 ) | measured: 2.25 to 2.36; calculated: 2.33 |
| Cleavage | Please complete |
| colour | white, yellowish to salmon red |
| Line color | White |
| transparency | translucent |
| shine | Silky gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.514 n β = 1.515 n γ = 1.520 |
| Birefringence | δ = 0.006 |
| Optical character | biaxial positive |
| Axis angle | 2V = measured: 52 °; calculated: 50 ° |
Gonnardite is a rather seldom occurring mineral from the mineral class of " silicates and germanates " with the chemical composition (Na, Ca) 2 [(Si, Al) 5 O 10 ] · 3H 2 O, so it is a water-containing sodium silicate. The elements sodium and calcium or silicon and aluminum indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral. Structurally Gonnardite one of the framework silicates ( tectosilicates ) and there to the group of zeolites .
Gonnardite crystallizes in the tetragonal crystal system and develops fibrous to prismatic crystals , which are mostly arranged in radial to spherical or kidney - shaped mineral aggregates . He can also appear in massive crowds.
In its pure form, gonnardite is colorless and transparent. Due to the multiple refraction of light due to the predominantly polycrystalline formation, however, it usually appears white; in addition, it can take on a yellowish to salmon-red color due to foreign admixtures, whereby the transparency decreases accordingly. The rare, macro- crystalline forms show a glass-like sheen on the crystal surfaces . In dense, fibrous aggregate forms, gonnardite usually shimmers like a silk or mother-of-pearl.
Etymology and history
Gonnardite was first discovered at La Chaux de Bergonne near the municipality of Gignat in the French canton of Saint-Germain-Lembron (Auvergne) and described in 1896 by Antoine Lacroix , who named the mineral after Ferdinand Gonnard (1833-1923).
Type material of the mineral is in the Natural History Museum in London (England) under the catalog no. 1930.166 kept.
classification
In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the gonnardite belonged to the department of "tectosilicates (tectosilicates), with zeolites ", where together with mesolite , natrolite , paranatrolite , skolezite , thomsonite (Ca) and thomsonite - (Sr) the group of "fiber zeolites I" with the system no. VIII / J.21 formed.
The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns the gonnardite to the already more finely subdivided division of “tectosilicates with zeolitic H 2 O; Family of zeolites ”. This is also further subdivided according to the crystal structure, so that the mineral can be found in the sub-section “Zeolites with four-ring chains connected via a fifth Si”, where it is only found together with mesolite, natrolite, paranatrolite and skolezite "Natrolith group" with the system no. 9.GA.05 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the gonnardite to the class of "silicates and Germanates" and there in the department of "structural silicates: zeolite group". Here it is in the " Natrolith and related species " with the system no. 77.01.05 to be found in the subsection "Real Zeolites".
Crystal structure
Gonnardite crystallizes tetragonally in the space group I 4 2 d (space group no. 122) with the lattice parameters a = 13.21 Å and c = 6.62 Å as well as one formula unit per unit cell .
Education and Locations
Gonnardite forms hydrothermally in cavities in volcanic rocks such as basalt , tephrite or weathered skarn , where it usually occurs in association with other zeolites, but also with calcite .
As a rather rare mineral formation, gonnardite can sometimes be abundant at various sites, but overall it is not very common. A total of around 170 sites are known to date (as of 2016). Its type locality La Chaux de Bergonne is the only known site in France to date , but the mineral could still be found on the island of Réunion , which is part of French territory , more precisely on the Piton des Neiges volcano , as well as in basaltic rock samples from the territory of the French southern and Antarctic territories Grande Terre Island to be demonstrated.
In Germany, the mineral was found on the Wartberg near Selb in Bavaria, among other places ; in the quarries "Roßberg" near Roßdorf (near Darmstadt) , "Hochberg" near Nieder-Ofleiden and "Gaulsberg" near Ortenberg in Hesse; in the “Bramburg” quarry near Adelebsen in Lower Saxony; in the Weilberg quarry near Königswinter in North Rhine-Westphalia; on the Arensberg near Zilsdorf and on the Schellkopf near Brenk in the Rhineland-Palatinate Eifel and in a phonolite quarry on the Maar of Hammerunterwiesenthal in Saxony.
In Austria, gonnardite has so far only been discovered in an unnamed basalt quarry near Klöch and in the “Steinberg” quarry near Mühldorf near Feldbach in Styria, and in Switzerland the mineral is only known from the Forno glacier and Piz dei Rossi in the canton of Graubünden .
Other locations include Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Costa Rica, Canada, France, Greenland, India, Italy, Japan, Kenya, Lesotho, New Zealand, Norway, Poland, Portugal, the Czech Republic, Greenland, Romania , Russia, the Solomon Islands, Spain, Turkey, Hungary, the United Kingdom (UK) and the United States of America (USA).
See also
literature
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 911 .
- Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 617 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 274 ( Dörfler Natur ).
Web links
- Mineral Atlas: Gonnardite (Wiki)
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names; August 2013 (PDF 1.3 MB)
- ↑ Webmineral - Gonnardite
- ^ A b c 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. 701 .
- ↑ a b Gonnardite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 77 kB )
- ↑ a b c d e Mindat - Gonnardite
- ↑ Mindat - Number of localities for Gonnardit
- ^ Mindat - Gonnardite from Piton des Neiges, Réunion Island
- ^ Mindat - Gonnardite from Grande Terre island, Kerguelen Islands, French Southern and Antarctic Lands
- ↑ Find location list for gonnardite at the Mineralienatlas and at Mindat