Afwillit
| Afwillit | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Silicates and Germanates - island silicates |
|
System no. to Strunz and to Dana |
9.AG.75 ( 8th edition : VIII / B.22) April 52, 07.01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic; m |
| Space group | Room group Cc ( room group no.9 ) |
| Lattice parameters |
a = 16.28 Å ; b = 5.63 Å; c = 13.24 Å β = 134.9 ° |
| Formula units | Z = 4 |
| Frequent crystal faces | {100}, {201} |
| Physical Properties | |
| Mohs hardness | 3 to 4 |
| Density (g / cm 3 ) | measured: 2.630; calculated: 2.643 (5) |
| Cleavage | perfect according to {10 1 }, good according to {100} |
| Break ; Tenacity | clamshell; brittle |
| colour | colorless, white |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.617 n β = 1.620 n γ = 1.634 |
| Birefringence | δ = 0.017 |
| Optical character | biaxial positive |
| Axis angle | 2V = 50 to 56 ° (measured) |
| Other properties | |
| Chemical behavior | Easily soluble in HF and HCl |
| Special features | piezoelectric |
Afwillit is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the composition Ca 3 [SiO 4 ] [SiO 2 (OH) 2 ] · 2H 2 O, so it is chemically a water-containing calcium silicate, which structurally belongs to the island silicates .
Afwillit mostly develops tabular to prismatic crystals stretched and streaked along the b-axis , but can also be found in the form of radial, fibrous, spherulitic or massive mineral aggregates . The surfaces of the colorless and transparent or, in the case of polycrystalline formation, white crystals show a glass-like sheen .
Etymology and history
Afwillit was first established in 1923 by the then general director of De Beers Consolidated Mines Alpheus Fuller Williams (1874-1953) in the "Dutoitspan Mine" near Kimberley in South Africa, more precisely at a depth between 500 and 750 ft (corresponds to about 152 to 228 m) in a large dolerite - inclusion in kimberlite , discovered.
The mineral was analyzed and described in 1925 by John Parry and Frederick Eugene Wright , who named it after its discoverer ( AFWill for short ).
classification
In the now outdated, but still in use, 8th edition of the mineral classification according to Strunz , the Afwillit belonged to the department of "Island silicates with non-tetrahedral anions (Neso subsilicates)", where together with Spurrit he formed the "Spurrit-Afwillit Group" with the system No. VIII / B.22 and the other members Bultfonteinit , Fukalith , Harrisonit , Hatrurit , Nagelschmidtit , Olmiit , Paraspurrit , Poldervaartit and Ternesite .
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies Afwillit in the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral according to its composition and structure is classified in the subsection “Island silicates with additional anions; Cations in mostly [6] er and> [6] er coordination “can be found, where the unnamed group 9.AG.75 is the only member .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Afwillit to the class of "silicates and germanates" and there in the department of "island silicates: SiO 4 groups and O, OH, F and H 2 O". Here it is together with Bultfonteinit, Hatrurit and Jasmundit in the " Afwillit and related species " with the system no. April 52, 2007 within the subsection “ Island silicates: SiO 4 groups and O, OH, F and H 2 O with cations in [6] and / or> [6] coordination”.
Crystal structure
Afwillit crystallizes monoclinically in the space group Cc (space group no. 9) with the lattice parameters a = 16.28 Å ; b = 5.63 Å; c = 13.24 Å and β = 134.9 ° and 4 formula units per unit cell .
properties
Afwillit is piezoelectric , that is, like quartz , it builds up an electrical voltage with changing elastic deformation.
The mineral is easily soluble in HF and HCl .
Education and Locations
Afwillit is formed as a conversion product in limestone that has been modified by contact metamorphosis . The accompanying minerals include apophyllite , brucite , calcite , ettringite , foshagite , gehlenite , hillebrandite , merwinite , natrolite , portlandite , spurrite and thaumasite .
As a rare mineral formation, Afwillit has only been found at a few sites so far, with around 30 sites being known to date (as of 2013). In addition to its type locality "Dutoitspan Mine" near Kimberley , the mineral was also found in South Africa in the "N'Chwaning Mines" near Kuruman and in the "Wessels Mine" near Hotazel in the manganese fields of the Kalahari .
In Germany, Afwillit was found on the Zeilberg in Bavaria and in several places in the Vulkaneifel (Daun, Mayen, Mendig).
The only known site in Austria so far is a basalt quarry in the market town of Klöch in the district of Southeast Styria.
Other well-known sites include Boisséjour / Ceyrat in France, Inishcrone in Ireland and Carneal and Scawt Hill in County Antrim , which belongs to Northern Ireland , the "Hatrurim Formation" in the Negev desert and the river Ajalon in Israel, several sites in Italy that "Mihara" and "Fuka" mines in Okayama Prefecture on the Japanese island of Honshū, Tokatoka on the North Island of New Zealand, Oravița and Racoş ( Harghita County ) in Romania; the river Nizhnyaya Tunguska , the Yoko-Dovyrensky massif near Lake Baikal in the Republic of Buryatia and the Mount Lakargi in the Republic of Kabardino-Balkaria in Russia as well as the Sky Blue Hill in Riverside County (California) and the "Pea Ridge Mine" near Sullivan ( Missouri) in the United States.
See also
literature
- John Parry, FE Wright: Afwillite, a new hydrous calcium silicate, from Dutoitspan mine, Kimberley, South Africa , In: Mineralogical Magazine , Volume 20 (1925), pp. 277–285 ( PDF 372.6 kB )
Web links
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names (February 2013) (PDF 1.3 MB)
- ↑ Daniel Atencio, Nikita V. Chukanov, Fabrizio Nestola, Thomas Witzke , José MV Coutinho, Aleksandr E. Zadov, Reynaldo R. Contreira Filho, Gunnar Färber: Mejillonesite, a new acid sodium, magnesium phosphate mineral, from Mejillones, Antofagasta, Chile , In: American Mineralogist , Volume 97 (2012), p. 20
- ^ 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. 558 .
- ↑ a b c Afwillite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 73.6 kB )
- ↑ a b c d e Mindat - Afwillite
- ↑ Mindat - Number of localities for Afwillite
- ↑ Find location list for Afwillit in the Mineralienatlas and Mindat