Afwillite
- Ca3 [ SiO4 ] [ SiO2 ( OH ) 2] · 2H2O
- Ca12 (H2O) 8 [ SiO4 ] 4 [ SiO2 ( OH ) 2] 4
Afwillit is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic crystal system with the composition Ca3 [ SiO4 ] [ SiO2 ( OH ) 2] · 2H2O, is thus seen chemically a hydrous calcium silicate, which structurally belongs to the island silicates.
Afwillit developed mostly tabular to prismatic, elongated according to the b-axis and striped crystals, but is also found in the form radialstrahliger, fibrous, or massive Globular graphite mineral aggregates. The surfaces of the colorless and transparent or white in polycrystalline form crystals show a glass-like shine.
Special Features
Afwillit is piezoelectric, meaning it builds similar to quartz with varying elastic deformation of an electrical voltage.
The mineral is easily soluble in HF, and HCl.
Etymology and history
Afwillit was the first time in 1923 by the then Director General of the De Beers Consolidated Mines Alpheus Fuller Williams ( 1874-1953 ) in the " Dutoitspan Mine" near Kimberley in South Africa, more specifically ft at a depth 500-750 (equivalent to approximately 152-228 m) in a large dolerite inclusion in kimberlite discovered.
Analyzed and described the mineral in 1925 by John Parry and Frederick Eugene Wright, who named it after its discoverer (abbreviated AFWill ).
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Afwillit belonged to the department of " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) " where he along with spurrite the " spurrite - Afwillit group " with the system No. Formed VIII/B.22 and the other members Bultfonteinit, Fukalith, Harrisonit, Hatrurit, Nagelschmidtit, Olmiit, Paraspurrit, Poldervaartit and Ternesit.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Afwillit also in the department of " island silicates ( nesosilicates ) ". This is further subdivided according to the possible presence of other anions and the coordination of the cations involved, so that the mineral according to its composition and its construction in the subsection " island silicates with additional anions; Cations can be found in most cases and > coordination, " where the only member is the unnamed group 9.AG.75.
The mainly common in English-speaking classification of minerals according to Dana assigns the Afwillit in the class of " silicates and Germanates " and then in the Department of: an " island silicates SiO4 Groups and O, OH, F, and H2O". Here he is with Bultfonteinit, Hatrurit and Jasmundit in the " Afwillit and related species " with the system no. ": With cations and / or SiO4 Groups and O, OH, F, and H2O > coordination island silicates " to find 52.04.07 within the subdivision.
Education and Locations
Afwillit forms as a conversion product in kontaktmetamorph altered limestone. Accompanying minerals occur among others Apophyllite, brucite, calcite, ettringite, Foshagite, gehlenite, hillebrandite, merwinite, Natrolite, portlandite, spurrite and thaumasite.
A rare mineral formation Afwillit could be proven so far only in a few localities, where so far (as of 2013) are considered to be known about 30 localities. Apart from its type locality " Dutoitspan Mine" near Kimberley the mineral still occurred in South Africa in the " N'Chwaning mines " at Kuruman and in the " Wessels Mine " at Hotazel in the fields of the Kalahari manganese apparent.
The only known locality in Austria is a basalt quarry in the market town in the district Klöch Südoststeiermark.
Other known localities include Boisséjour / Ceyrat in France, Inishcrone in Ireland and Carneal and Scawt Hill in the belonging to Northern Ireland County Antrim that, " Hatrurim formation" in the Negev desert and the River Ayalon in Israel, several find sites in Italy pits " Mihara " and " Fuka " in Okayama Prefecture on the Japanese island of Honshu, Tokatoka on the North island of New Zealand, Oraviţa and RACOS ( Harghita county ) in Romania; the flow Nizhnyaya Tunguska, the Yoko - Dovyrensky solid near Lake Baikal in the Republic of Buryatia and the mountain Lakargi in the Republic of Kabardino -Balkaria in Russia, and the Sky Blue Hill in Riverside County ( California ) and the " Pea Ridge Mine " Sullivan ( Missouri) in the USA.
Crystal structure
Afwillit crystallizes in the monoclinic space group Cc ( Raumgruppen-Nr. 9) with the lattice parameters a = 16.28 Å; b = 5.63 Å; c = 13.24 Å and β = 134.9 °, and four formula units per unit cell.