Tetradymite

Tetradymite is a rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the trigonal crystal system with the chemical composition Bi2Te2S and usually developed millimeter - to centimeter-sized, pyramidal crystals in characteristic crystal twins and quadruplets, but also foliated to massive mineral aggregates to light steel-gray color, which often start colorful color of zinnweißer.

Etymology and history

Was first discovered in 1831 at tetradymite Župkov in bird mountains in Slovakia and described by Haidinger, who named the mineral after the Greek word tetradymos ( four times).

Classification

In the 8th edition of the now outdated Strunz'schen Mineral classification of tetradymite belongs to the department of " sulfides and sulfosalts with the molar ratio of metal: sulfur, selenium, tellurium <1: 1", where he and along with Kawazulith, Paraguanajuatit, Skippenit, Tellurantimon Tellurobismutit own group forms.

Since the 2001 revised 9th edition of the Strunz'schen classification of minerals, the class of sulfides and sulfosalts is firstly extended to the selenides, tellurides, arsenides, antimonides, bismuthides, Sulfarsenite, Sulfantimonite and Sulfbismuthite and on the other part, fine divided according to the type the cations involved in the connection. The tetradymite is thus now in the department of " metal sulfides with M: S = 3: 4 and 2: 3 " to find where the mineral together with Aleksit, Babkinit, Baksanit, Hedleyit, Ikunolit, Ingodit, Joseit -A, Joseit - B, Joseit -C, Kawazulit, Kochkarit, Laitakarit, Nevskit, Paraguanajuatit, Pilsenit, Poubait, Protojoseit, Rucklidgeit, Saddlebackit, Skippenit, Sulphotsumoit, Sztrókayit, Tellurantimon, Tellurobismutit, Telluronevskit, Tsumoite and Vihorlatit in the subdivision with " variable molar ratio of M: S "stands.

The commonly used in English-speaking classification of minerals according to Dana assigns the tetradymite also in the class of sulfides, there, however, in the department of " sulfides - including selenides and tellurides - with the ( general ) composition AmBnXp, with (m n): p = 2:3 ". Here he is as Leitmineral together with Tellurobismutit, Tellurantimon, Paraguanajuatit, Kawazulit and Skippenit the subdivision " 2.11.7 Tetradymitgruppe ( Trigonal: ) "

Education and Locations

Tetradymite usually formed by hydrothermal processes in the medium to hochgradiegen gold deposits, but also by contact metamorphism. There in paragenesis occurs among other native gold, silver, tellurium, hessite, petzite, pyrite, galena and sphalerite.

Could Worldwide tetradymite so far (as of 2010) are detected at around 330 localities, as, inter alia, Argentina, Armenia, Australia, Belgium, Bolivia, Brazil, Bulgaria, China, Germany, Finland, France, Greece, Japan, Canada, Kazakhstan, Mexico, New Zealand, Norway, Austria, Poland, Romania, Russia, Sweden, Switzerland, Serbia, Zimbabwe, Slovakia, Spain, South Africa, Tanzania, Turkey, Czech Republic, Ukraine, Hungary, United Kingdom ( UK) and in the United States of America.

Crystal structure

Tetradymite trigonal crystallized in the space group with the lattice parameters a = 4.24 Å and c = 29.59 Å and three formula units per unit cell.