Willemite
| Willemite | |
|---|---|
 Size: 3.2 × 2.3 × 1.3 cm |
|
| General and classification | |
| chemical formula | Zn 2 [SiO 4 ] |
|
Mineral class (and possibly department) |
Silicates and germanates - island silicates (nesosilicates) |
|
System no. to Strunz and to Dana |
9.AA.05 ( 8th edition : VIII / A.01) 51.01.01.02 |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | trigonal-rhombohedral 3 |
| Space group | R 3 |
| Lattice parameters | a = 13.94 Å ; c = 9.31 Å |
| Formula units | Z = 18 |
| Frequent crystal faces | {10 1 0}; {10 1 1}; {30 3 4} |
| Physical Properties | |
| Mohs hardness | 5.5 |
| Density (g / cm 3 ) | 3.9 to 4.2 |
| Cleavage | indistinct after {0001} and {1120} |
| Break ; Tenacity | mussel-like to uneven, splintery |
| colour | colorless, white, red, green-yellow |
| Line color | White |
| transparency | transparent to opaque |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.691 to 1.694 n ε = 1.719 to 1.725 |
| Birefringence | δ = 0.028 |
| Optical character | uniaxial positive |
| Other properties | |
| Special features | strong light green fluorescence |
The mineral willemite , also known by its outdated, mining name Belgit or Hebertin or Villemit , is a relatively rare island silicate from the phenakite group . It crystallizes in the trigonal crystal system with the chemical composition Zn 2 [SiO 4 ] and develops mostly prismatic, tabular crystals , but also radial, grainy aggregates of white, red or green-yellow color. Colorless crystals are also known.
Special properties
The outstanding property of willemite is its strong, light green fluorescence under short and long wave UV light as well as when irradiated with electron beams . Therefore, it was often used as a luminescent material for so-called magic eyes , a now obsolete optical display tube in radio technology. It should be noted, however, that the strength of the fluorescence is subject to large fluctuations depending on the location. The mineral finds from Franklin Hill and Sterling Hill in New Jersey are among the most powerfully fluorescent. In contrast , the willemites in the so-called “ iron hat ” that were not recorded by the metamorphosis (see also section on formation and localities ) show no fluorescence.
Willemite has a Mohs hardness of 5.5 and a density of 3.9 to 4.2 g / cm 3 . The transparent to opaque crystals show resin to glass gloss on the surfaces.
Etymology and history
Willemit was named in honor of Wilhelm I (1772–1843, King of the Netherlands) after him. The mineral was first found in Kelmis in 1830 (previously also known as Altenberg and mainly because of the local zinc mine and foundry Vieille Montagne ) and described by Armand Lévy .
classification
According to the old (8th edition) and new systematics of minerals (9th edition) according to Strunz , the willemite belongs to the island silicates (nesosilicates). In the new system, however, this division has been further subdivided and the mineral can now be found in the subdivision of island silicates without further anions with cations in tetrahedral [4] coordination .
The systematics of the minerals according to Dana also assigns the willemite to the department of island silicates. However, the subdivision only restricts the arrangement of the cations that are arranged in [4] coordination. In the Dana system, the minerals willemite, eucryptite and phenakite form the phenakite group .
Modifications and varieties
Currently (as of 2008) two varieties of willemite are known: the xingshaoite enriched with 25.4% cobalt (II) oxide (CoO) and the manganese-containing troostite .
Education and Locations
Willemite is formed either as a secondary mineral in zinc - deposits or through metamorphosis in marble . Accompanying minerals include cerussite , fragranceite , glaucomaite , hemimorphite , franklinite , malachite , mimetite , nasonite , rosasite , smithsonite and zincite .
In addition to its type locality Kelmis, it was found among others in San Luis in Argentina ; South and West Australia ; the provinces of Liège and Limburg in Belgium ; Hesse , Lower Saxony , North Rhine-Westphalia and Saxony in Germany ; Liguria , Sardinia and Tuscany in Italy ; Québec , Newfoundland and Labrador in Canada ; Katanga in the Democratic Republic of the Congo ; Grootfontein and Tsumeb in Namibia ; Carinthia in Austria ; Dalarna , Värmland and Västmanland in Sweden ; as well as various regions in the US .
Crystal structure
Willemite crystallizes in the trigonal crystal system in the space group with the lattice parameters a = 13.94 Å and c = 9.31 Å as well as 18 formula units per unit cell .
Individual evidence
- ↑ a b c d Webmineral - Willemite (Engl.)
- ↑ a b Willemite at mindat.org (engl.)
- ↑ Stefan Weiß: The large Lapis mineral directory . 4th edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6 .
- ^ Paul Ramdohr , Hugo Strunz : Klockmanns textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 .
- ↑ Mineralien-Lexikon - Willemit ( Memento of the original from January 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ MinDat - Localities for Willemite (Engl.)
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 .
Web links
- Mineral Atlas: Willemite (Wiki)