Wurtzit

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Wurtzit
Wurtzite-176485.jpg
Wurtzite in a hexagonal, tabular formation from the Yaogangxian Mine, Hunan, China
General and classification
other names

β-zinc sulfide (β-ZnS)

chemical formula ZnS
Mineral class
(and possibly department) 		Sulfides, sulfosalts
System no. to Strunz
and to Dana 		2.CB.45 ( 8th edition : II / C.13)
08/02/07/01
Similar minerals Sphalerite , Matrait , Greenockite , Rambergite , Cadmoselite
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-pyramidal; 6 mm
Space group P 6 3 mc (No. 186)Template: room group / 186
Lattice parameters a  = 3.82  Å ; b  = 3.82 Å; c  = 6.26 Å
Formula units Z  = 2
Frequent crystal faces Pyramids: {50 5 2}, {10 1 0}, (0001)
tabular crystals: (0001)
Twinning very rare
Physical Properties
Mohs hardness 3.5 to 4
Density (g / cm 3 ) 3.98 to 4.08
Cleavage completely after {10 1 0}
clearly after (0001)
Break ; Tenacity uneven
colour black, brown, brownish red
Line color light brown
transparency translucent
shine Diamond luster
Crystal optics
Refractive indices n ω  = 2.356
n ε  = 2.378
Birefringence δ = 0.022
Optical character uniaxial positive
Other properties
Chemical behavior almost insoluble in water
Special features piezoelectric , fluorescent orange-red under long-wave UV light

Wurtzite , also known as beta zinc sulfide (β-ZnS), is a rather seldom occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the hexagonal crystal system and is the metastable high-temperature modification of the cubic sphalerite . Wurtzite usually forms radial aggregates of needle-shaped crystals or pyramidal single crystals (more rarely also tabular) with a black to brown-red color.

Etymology and history

Charles Adolphe Wurtz, ca.1870

The first description of Wurtzite comes from the French chemist and mineralogist Charles Friedel (1832–1899) in 1861. He named the mineral after his teacher Charles Adolphe Wurtz (1817–1884) in recognition of his scientific merits. The samples examined by Friedel were found in the San José mine near the city of Oruro in the Bolivian Andes , which was an important mining site until the 20th century, mainly due to the mining of tin . Oruro is still the type locality of the Wurtzit today.

Since the founding of the International Mineralogical Association , Wurtzit has been the internationally recognized mineral name for hexagonally crystallizing zinc sulfide or β-ZnS.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the wurtzite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with the molar ratio of metal: sulfur, selenium, tellurium = 1: 1", where together with cadmoselite , greenockite , rambergite and wurtzite-2H it formed an independent 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 wurtzite to the class of “sulfides and sulfosalts” and there to the department of “metal sulfides with the molar ratio M: S = 1: 1 (and similar) ”. However, this section is further subdivided according to the predominant metals in the compound, so that the mineral can be found in the sub-section "with zinc (Zn), iron (Fe), copper (Cu), silver (Ag) etc." is where it is named after the "Wurtzit Group" with the system no. 2.CB.45 and the other members cadmoselite, greenockite, hypercinnabarite and rambergite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns wurtzite to the class of "sulphides and sulphosalts" and there to the "sulphide minerals" category. Here he is also the namesake of the "Wurtzit group (Hexagonal: P63mc)" with the system no. 02.08.07 and the other members Greenockite, Cadmoselite and Rambergite can be found within the subdivision of " Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 1 ".

Crystal structure

Crystallographic Data
Crystal structure of wurtzite
Wurtzite structure
Crystal system hexagonal
Space group P 6 3 mc
Lattice parameter
(unit cell )		 a  (=  b ) = 3.82  Å
c  = 6.26 Å
Number ( Z ) of the
formula units 		Z  = 2

Wurtzite crystallizes in the hexagonal crystal system in the space group P 6 3 mc (space group no.186) with the lattice parameters a  = 3.82  Å and c  = 6.26 Å and two formula units per unit cell . The structure of the crystal structure can be derived from that of Lonsdaleit , the hexagonal diamond . This is analogous to the structure of sphalerite , which can be derived from normal cubic diamonds. Template: room group / 186

The "wurtzite structure" named after him consists of a hexagonal closest packing of spheres (stacking sequence ... ABAB ... in the direction of the crystallographic c- axis) of sulfur atoms , half of which are occupied by zinc atoms in the tetrahedron . Since there are twice as many tetrahedral gaps as there are packing particles (in this case sulfur) in a close packing of spheres and only every second gap is occupied by zinc, this results in a sulfur-zinc ratio of 1: 1 and thus the chemical formula ZnS. The structure of the wurtzite can also be described in reverse, i.e. This means that the zinc atoms form the hexagonal closest packing of spheres with the sulfur atoms in half of the tetrahedral gaps, sulfur and zinc form what are known as commutative partial lattices . Both types of atoms each have a coordination number of 4, and the coordination polyhedron in both cases is an undistorted tetrahedron . Using the Niggli notation , the structure can be represented as follows:

The wurtzite structure is one of the most important types of crystal structure, numerous technically important compounds crystallize isotypically to wurtzite (i.e. with the same crystal structure), including zinc oxide  (ZnO), cadmium sulfide  (CdS), cadmium selenide  (CdSe), gallium nitride  (GaN) and silver iodide ( Jodargyrit , AgI).

The wurtzite structure competes with the cubic zinc blende structure , which is important for semiconductor physics. B. the system gallium arsenide (GaAs) in contrast to gallium nitride (GaN) not in the hexagonal wurtzite structure, but in the zinc blende structure.

properties

When heated with oxygen ( roasting ), wurtzite breaks down into zinc oxide just like sphalerite . This decay was previously used, among other things, for qualitative zinc detection: sublimed zinc oxide is deposited on the carbon in front of the soldering tube. This is lemon yellow when hot (see also zinc suboxides ) and only takes on the typical white color of zinc oxide when it has cooled down.

morphology

Wurtzite often occurs as a radial aggregate of several needle-shaped to columnar crystals together with sphalerite in the so-called shell diaphragm . The wurtzite aggregates are similar in shape to those of stibnite (Sb 2 S 3 ). Isolated single crystals are more rarely formed as mostly imperfect pyramids . The shape of such crystals is also referred to as hemimorph ("half-shaped") in mineralogy , as the two ends of the crystal differ greatly in their appearance (base on one side, top of the pyramid on the other). Tabular crystals can also be observed very rarely, the upper and lower boundary surfaces of which run parallel to the pyramid base surface; in this case the pyramid surfaces are not formed.

Modifications and varieties

Voltzine from Sterling Mine, Sterling Hill, Ogdensburg , Franklin Mining District, Sussex County, New Jersey , USA

As Voltzin a mixture of wurtzite and organic matter is referred to.

Education and Locations

Wurtzite (brown) and galena (silvery) from Potosí , Bolivia (size 9.2 cm × 8.6 cm × 3.5 cm)

Like most sulphides, wurtzite is usually formed by precipitation from hydrothermal solutions . Naturally formed wurtzite usually contains traces of iron , manganese and cadmium . Above all, high cadmium contents favor the formation of wurtzite compared to sphalerite (α-ZnS). Accompanying minerals ( parageneses ) of wurtzite are usually sphalerite and galena (PbS) as well as other, often iron-rich sulfides and disulfides such as pyrite (FeS 2 ), marcasite (FeS 2 ) and chalcopyrite (CuFeS 2 ).

In total, Wurtzite has so far (as of 2011) been found in more than 300 sites. In addition to its type locality "San José Mine" near the city of Oruro , the mineral occurred in Bolivia in the mines near Huanuni (Pantaleón Dalence province), Callipampa ( Poopó province ), Municipio Pazña and Municipio Poopó in Oruro; Ayopaya Province in Cochabamba; Berenguela in the province of Pacajes (La Paz) as well as near Potosí and in several places in the province of Antonio Quijarro , in the municipality of Chayanta , in the province of Rafael Bustillo and the province of Sur Chichas in the department of Potosí. The best and largest wurtzite crystals with a diameter of up to four centimeters ( animas ) have also been found in Bolivia .

In Germany, Wurtzit was found at Hornbühl near Waldkirch , in the “Silbereckle” and “Michael” mines near Reichenbach (Lahr) and “Segen Gottes” near Wiesloch in Baden-Württemberg; near Muglhof ( pastures in the Upper Palatinate ) in Bavaria; near Rachelshausen in Hesse; in several places in Stolberg and Hellenthal as well as in Wirtenbach and Marl -Hüls in North Rhine-Westphalia; in the "Einheit" pit near Elbingerode in Saxony-Anhalt; in several places in the Saxon Ore Mountains and in the Thuringian municipality of Niedersachswerfen .

In Austria the mineral could be found in the mines "Rudolph" and "Stephanie" near Bad Bleiberg , "Franz Josef" near Heiligengeist and "Max" near Kreuth in Carinthia; at the Semmering Pass in Lower Austria and at the Tschirgant and Karwendel Mountains in Tyrol.

In Switzerland, Wurtzit has so far only been found near Biel / Bienne in the canton of Bern and the Lengenbach mine in the Binn valley in the canton of Valais.

Talnach ( Talnakh ) in Siberia (Russia), where well-developed crystals of up to three centimeters have been found, is worth mentioning due to the extraordinary finds of wurtzite .

Other locations are Afghanistan , Argentina , Australia , Bulgaria , China , France , Greece , Canada , Kazakhstan , Kyrgyzstan , India , Iran , Ireland , Italy , Japan , Mexico , Morocco , Namibia , the Netherlands , Peru , Poland , Portugal , Romania , Zambia , Sweden , Slovakia , Slovenia , Spain , South Africa , Tajikistan , the Czech Republic , Ukraine , Hungary , the United Kingdom (Great Britain) and the United States of America (USA).

Wurtzite could also be detected in rock samples from the Mid-Atlantic Ridge , the Red Sea , the Bismarck Sea and the East Pacific Ridge as well as outside the Earth on the moon , more precisely near the Luna-24 landing site in the Mare Crisium .

See also

literature

Web links

Commons : Wurtzit  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d EH Kisi, MM Elcombe: U parameters for the wurtzite structure of ZnS and ZnO using powder neutron diffraction. In: Acta Crystallographica . No. C45, 1989, pp. 1867-1870
  2. ↑ a b c d Wurtzit at mindat.org (English)
  3. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  4. ↑ a b List of localities for wurtzite in the Mineralienatlas and in Mindat