Acanthite

• Silver sheen

Acanthite (obsolete silver luster ) is a rarely occurring mineral from the mineral class of sulfides and sulfosalts with a molar ratio of metal: sulfur ( selenium, tellurium )> 1: 1 It crystallizes in the monoclinic crystal system with the chemical composition Ag2S and developed mostly needle-shaped or narrow-minded, often pseudo-cubic crystals, but also massive aggregates of gray to black color.

Etymology and history

Akanthit was first discovered akanta named at Jáchymov ( German Jáchymov ) in the Czech Republic and described in 1855 by Gustav Adolf Kenngott ( 1818-1897 ), the ἄκων the mineral because of its eye-catching crystal form after the Greek word for thorn or sting.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Akanthit belonged to the mineral class of " sulfides and sulfosalts " and then to the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 along with Aguilarit, argentite, Benleonardit, Cervelleit, Empressit, hessite, Chenguodait (IMA 2004 - 042A ), Naumannite, Tsnigriit and Stützit the independent group II/B.05 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Akanthit also in the class of " sulfides and sulfosalts " and there in the department of "Metal Sulfides, M: S> 1: 1 ( mainly 2: 1) " a. This division, however, is further subdivided according to the nature of the cations involved, so that the mineral is found according to its composition in the subdivision " with copper ( Cu), silver (Ag ) and / or gold ( Au) " where there is only together with argentite is the unnamed group 2.BA.30a.

The classification of minerals according to Dana assigns the acanthite in the class of " sulfides and sulfosalts " and then in the Department of " sulfide minerals ." Here he is named the " Akanthitgruppe " with the system no. 02:04:01 and the other members Naumannite and Aguilarit within the subdivision " sulfides - tellurides and selenides, including - with the composition AmBnXp, with (m n): p = 2:1 " to find.

Modifications and varieties

Acanthite is the monoclinic low temperature modification of the cubic argentite, that transforms on cooling below 173 ° C, its crystal system. But, while retaining often the outer crystal form of argentite at ( Paramorphose ).

Education and Locations

Acanthite is formed hydrothermally in silver ore - passes. Accompanying minerals are argentite addition, Silver, Proustite, Pyrargyrite and others galena, acanthite which is often included.

In Germany, found the mineral, among others in the Black Forest in Baden- Württemberg; im Fichtelgebirge, Bavaria and Upper Palatinate Forest in Bavaria; in the Odenwald and Taunus in Hesse; in the Harz Mountains in Lower Saxony; at several points Fund in North Rhine -Westphalia; in the Eifel and Hunsrück on in Rhineland -Palatinate; in the Saarland; in Saxony -Anhalt; at Annaberg, Schneeberg and many other parts of Saxony and Thuringia.

In Austria Akanthit occurred mainly in the regions Carinthia, Lower Austria, Salzburg, Styria and Tyrol.

In Switzerland, the mineral previously could only be found in Miglieglia in Ticino, in the Binn Valley and in Loetschental in the canton of Valais.

Other localities are Argentina, Armenia, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Ecuador, El Salvador, France, Georgia, Greece, Greenland, Honduras, Indonesia, Iran, Ireland, Italy, Japan, Canada, Kazakhstan, Colombia, Madagascar, Morocco, Mexico, Mongolia, Namibia, New Zealand, Nicaragua, Norway, Papua New Guinea, Peru, Poland, Portugal, Romania, Russia, Saudi Arabia, Sweden, Slovakia, Slovenia, Spain, South Africa, South Korea, Tajikistan, Czech Republic, Turkey, Ukraine, Hungary, Uzbekistan, the U.S. Virgin Islands, the United Kingdom ( UK) and the United States of America (USA).

Even in rock samples of the Mid-Atlantic Ridge and the moon, the Luna 24 mission brought back Akanthit could be found.

Crystal structure

Akanthit crystallizes in the monoclinic space group P21 / n ( Raumgruppen-Nr. 14) with the lattice parameters a = 4.23 Å; b = 6.93 Å; c = 7.86 Å and 99.6 ° β = 4 and formula units per unit cell.

Use

Acanthite is one of the main raw materials for the production of silver.