Willemseit
| Willemseit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (Ni, Mg) 3 [(OH) 2 | Si 4 O 10 ] |
|
Mineral class (and possibly department) |
Silicates and germanates - layered silicates |
|
System no. to Strunz and to Dana |
9th EC.05 ( 8th edition : VIII / H.09) 71.02.01.04 |
| Similar minerals | Talk , Minnesotaite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Room group (no.) | C 2 / c (No. 15) |
| Lattice parameters |
a = 5.316 Å ; b = 9.149 Å; c = 18.994 Å β = 99.96 ° |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 2 |
| Density (g / cm 3 ) | 3.31 |
| Cleavage | {001} perfect |
| colour | light green |
| Line color | greenish white |
| transparency | Please complete |
| shine | Please complete |
| Crystal optics | |
| Refractive indices |
n α = 1.600 n β = 1.652 n γ = 1.655 |
| Birefringence | δ = 0.055 |
| Optical character | biaxial negative |
| Axis angle | 2V = 27 ° |
Willemseit (formerly pimelite ) is a very rare mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition (Ni, Mg) 3 [(OH) 2 | Si 4 O 10 ] and develops predominantly microcrystalline, coarse aggregates of light green color.
Etymology and history
Willemseit was first discovered in a nickel-containing rock sample that was recovered about 2 miles (about 3 km) west of the "Scotia Talk Mine" near Barberton in South Africa.
The mineral was described in 1968 by SA de Waal, who named the mineral after the South African geology professor Johannes Willemse . In addition to Willemseit, de Waal also discovered Nimit in this ore sample.
classification
In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Willemseite belonged to the mineral class of "silicates and Germanates" and then to the Department of " phyllosilicates (phyllosilicates)" where he collaborated with Ferripyrophyllit , Kegelit , Macaulayit , Minnesotait , Pyrophyllite and talc formed a separate 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 the Willemseit to the class of “silicates and germanates” and there to the “phyllosilicates” section. This division is, however, further subdivided according to the crystal structure, so that the mineral, according to its structure, can be found in the subdivision of "layered silicates (phyllosilicates) with mica tablets, composed of tetrahedral or octahedral networks", where it can only be found together with minnesotaite and talc forms the unnamed group 9.EC.05 .
The systematics of minerals according to Dana also assigns the Willemseit to the class of "silicates and Germanates" and there in the department of "layered silicate minerals". Here it is together with pyrophyllite, ferripyrophyllite, talc, minnesotaite and brinrobertsite in the "pyrophyllite talc group" with system no. 71.02.01 to be found in the subsection of " Layered Silicates: Layers of six-membered rings with 2: 1 layers ".
Education and Locations
Willemseit originated as a secondary mineral in a nickel-containing volcanic deposit and occurs mostly in paragenesis with millerite , nimite , goethite , opal , reevesite , ferrous trevorite and violarite , but also with falcondoite .
In addition to its type locality Barberton in the Mpumalanga province , Willemseit could also be found in South Africa at the Morokweng crater in the northwest province and near Bonao in the Monseñor Nouel province in the center of the Dominican Republic.
Crystal structure
Willemseit crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a = 5.316 Ångström , b = 9.149 Å, c = 18.994 Å and β = 99.96 ° and 4 formula units per unit cell .
See also
Individual evidence
- ↑ a b c d Webmineral - Willemseite (engl.)
- ↑ a b c d Willemseite at mindat.org (engl.)
- ↑ Martin Okrusch, Siegfried Matthes: Mineralogie: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3
- ↑ Willemseit mineral data sheet (English, PDF; 71 kB)
literature
- SA de Waal: Nickel minerals from Barberton, South Africa: III. Willemseite, a nickel-rich talc , In: The American Mineralogist , 1970, 55, 31-41 (English, PDF 646.7 kB)
Web links
- Mineralienatlas: Willemseit (wiki)