Wurtzite

β - zinc sulfide ( β - ZnS)

Referred wurtzite as beta - zinc sulfide ( β - ZnS), is a rare 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 radiating aggregates of acicular crystals or pyramidal crystals ( less commonly tabular ) with black to brownish red in color.

Special Features

When heated with oxygen ( roasting ) wurtzite decays as well as sphalerite for zinc oxide. This decay was formerly used among other things for the qualitative detection of zinc: on charcoal before the blowpipe is sublimed zinc oxide is deposited. This is when hot lemon yellow (see also Zinksuboxide ) and decreases only when cooled to the typical white color of the zinc oxide.

Etymology and history

The first description of wurtzite comes from the French chemist and mineralogist Charles Friedel (1832-1899) from the year 1861. He named the mineral after his teacher Charles Adolphe Wurtz ( 1817-1884 ), in recognition of its scientific merit. The investigated samples of Friedel were found in the San Jose mine near the city of Oruro in the Bolivian Andes, which was an important mining town up in the twentieth century, especially through the reduction of tin. Oruro is still the type locality of wurtzite.

Since the founding of the International Mineralogical Association wurtzite is the internationally recognized name for the mineral crystallized hexagonal zinc sulfide or β - ZnS.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the wurtzite belonged to the mineral class of " sulfides and sulfosalts " and then to the Department of " sulfides with the molar ratio of metal: sulfur, selenium, tellurium = 1: 1 ," where he formed a distinct group with Cadmoselit, Greenockit, Rambergit and wurtzite -2H.

The 9th edition used since 2001, valid and of the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the wurtzite also in the class of " sulfides and sulfosalts " and there in the department of " metal sulfides with the molar ratio M: S = 1: 1 ( and similar ) " a. This division, however, is further subdivided according to the dominant in the metal compound, so that the mineral according to its composition in the subsection " with zinc (Zn ), iron ( Fe), copper (Cu), silver (Ag ), etc., " Finding is where it is named as the " Wurtzitgruppe " with the system no. Forms 2.CB.45 and the other members Cadmoselit, Greenockit, Hypercinnabarit and Rambergit.

The mainly common in English-speaking classification of minerals according to Dana assigns the wurtzite into the class of " sulfides and sulfosalts " and there in the department of " sulfide minerals ." He is also named as the " Wurtzitgruppe ( Hexagonal: P63mc ) " with the system no. 02:08:07 and the other members Greenockit, Cadmoselit and Rambergit within the sub-division of " sulfides - tellurides and selenides, including - with the composition AmBnXp, with (m n): p = 1:1" to find.

Education and Locations

Wurtzite formed as sulfides most usually by precipitation from hydrothermal solutions. Naturally formed wurtzite usually contains traces of iron, manganese and cadmium. Especially high cadmium content promote the formation of the wurtzite type opposite sphalerite ( ZnS - α ). Accompanying minerals ( mineral assemblages ) of wurtzite are usually sphalerite and galena (PbS ), and other, often iron-rich sulfides and disulfides such as pyrite ( FeS2 ), marcasite ( FeS2 ) and chalcopyrite ( CuFeS2 ).

Overall, wurtzite so far (as of 2011) are detected in more than 300 localities. Except at its type locality " San José Mine" near the city of Oruro the mineral still occurred in Bolivia in the mines at Huanuni ( province Pantalà Dalence ), Calli Pampa ( province Poopó ), Municipio Municipio Pazña and Poopó in Oruro; Ayopaya province in Cochabamba; Berenguela in the province Pacajes (La Paz ) and at Potosí and in several places in the province Antonio Quijarro, in the municipality of Chayanta in which Rafael Bustillo Province and Sur chichas in the department of Potosí. In Bolivia, the best ever and largest Wurtzitkristalle with up to four centimeters in diameter ( Animas ) were found.

In Germany they found on wurtzite Hornbühl in Waldkirch, in the pits " Silbereckle " and " Michael" in Reichenbach ( Lahr ) and " God's blessing " at Wiesloch in Baden- Württemberg; at Muglhof ( Weiden ) in Bavaria; Rachel Hausen in Hesse; in several places of Stolberg and Hellenthal and in Wirtenbach and Marl- Hüls in North Rhine -Westphalia; in the pit "unity" in Elbingerode in Saxony-Anhalt; at several locations in the Saxon Erzgebirge and in the Thuringian municipality Niedersachswerfen.

In Austria, the mineral could, among other things in the pits "Rudolph " and " Stephanie " in Bad Bleiberg, " Franz Josef" in the Holy Spirit and "Max" in Kreuth in Carinthia; on the Semmering Pass in Lower Austria, and at Tschirgant and in the Karwendel mountains in Tirol.

In Switzerland, wurtzite found so far only in Biel / Bienne in the canton of Bern and the pit Lengenbach in the Binn Valley in the canton of Valais.

Noteworthy due to exceptional Wurtzitfunde is, among other things Talnach ( Talnakh ) in Siberia (Russia), where well-developed crystals of up to three centimeters found.

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

Even in rock samples from the Mid-Atlantic Ridge, from the Red Sea, the Bismarck Sea and the East Pacific Rise and outside the earth on the moon, or more precisely near the Luna 24 landing site in Mare Crisium, wurtzite could be detected.

Morphology

Wurtzite often occurs as radiating aggregates of several needle-like to columnar crystals on sphalerite, together with the so-called shell aperture. The wurtzite aggregates resemble it in shape to those of stibnite ( Sb2S3 ). Rare isolated single crystals are formed as the most imperfect pyramids. The shape of these crystals is known in mineralogy as hemimorphic ( " semi -faceted " ), because the two ends of the crystal in their appearance very different (base surface on one side, top of the pyramid on the other side ). Rarely, tabular crystals can be observed, extending the upper and lower boundary surfaces parallel to the pyramid base surface, the pyramid surfaces are not formed in this case.

Crystal structure

Wurtzite crystallizes in the hexagonal crystal system in space group P63mc ( Raumgruppen-Nr. 186) with the lattice parameters a = 3.82 Å and c = 6.26 Å and two formula units per unit cell. The construction of the crystal structure can be derived from that of the lonsdaleite, the hexagonal diamond. This is in analogy to the structure of sphalerite, which can be derived from the normal cubic diamond.

The eponymous " wurtzite " structure consists of a hexagonal close -packed ( ABAB ... stacking sequence ... in the direction of the crystallographic c- axis) of sulfur atoms, the tetrahedral sites are half occupied by zinc atoms. Since twice as many tetrahedral holes as packing particles are in a close packing of spheres ( in this case, sulfur) and only every second gap is occupied by zinc, resulting in a sulfur - zinc ratio of 1:1 and thus the chemical formula ZnS. The structure of wurtzite can be described also vice versa, that is, the zinc atoms form the hexagonal close packing of the sulfur atoms in half of the tetrahedral holes, sulfur and zinc form so-called commutative sublattice. Both types of atoms each have a coordination number of 4, as coordination polyhedron is obtained in both cases an undistorted tetrahedron. Using the notation Niggli, the structure can be represented as follows:

The wurtzite structure is one of the main crystal structure types, many also industrially important compounds crystallize isotypic with wurtzite (i.e., having the same crystal structure), such as zinc oxide (ZnO ), cadmium sulfide (CdS ), cadmium selenide ( CdSe ), gallium nitride (GaN) and silver iodide ( Jodargyrit, AgI ).

The wurtzite structure is in competition with the cubic zinc blende structure, which is important for the semiconductor physics: So, for example, the system crystallized gallium arsenide ( GaAs), in contrast to gallium nitride (GaN ) in the hexagonal wurtzite structure, but in the zinc blende structure.