Acanthite
| Acanthite | |
|---|---|
 |
|
| General and classification | |
| other names |
Silver sheen |
| chemical formula | Ag 2 S |
|
Mineral class (and possibly department) |
Sulfides and sulfosalts |
|
System no. to Strunz and to Dana |
2.BA.30a ( 8th edition : II / B.05) 04/02/01/01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 1 / n (No. 14, position 2) |
| Lattice parameters |
a = 4.23 Å ; b = 6.93 Å; c = 7.86 Å β = 99.6 ° |
| Formula units | Z = 4 |
| Twinning | Polysynthetic according to { 1 11} and contact twins according to { 1 01} |
| Physical Properties | |
| Mohs hardness | 2 to 2.5 |
| Density (g / cm 3 ) | measured: 7.20 to 7.22; calculated: 7.24 |
| Cleavage | indistinct |
| Break ; Tenacity | uneven |
| colour | black, gray |
| Line color | lead gray |
| transparency | opaque |
| shine | Metallic luster |
Acanthite (outdated silver luster ) is a rather seldom occurring mineral from the mineral class of "sulfides and sulfosalts" with the chemical composition Ag 2 S, so it consists of silver and sulfur in a ratio of 2: 1 and is therefore chemically silver sulfide .
Acanthite crystallizes in the monoclinic crystal system and develops mostly needle-shaped or narrow-minded, often pseudocubic crystals , but also massive aggregates of gray to black color.
Etymology and history
Akanthite was first discovered near Jáchymov (German Sankt Joachimsthal ) in the Czech Republic and described in 1855 by Gustav Adolf Kenngott (1818–1897), who named the mineral after the Greek word ἄκανθα akantha for thorn or thorn because of its striking crystal shape .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the acanthite belonged to the mineral class of "sulfides and sulfosalts" and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 aguilarite , argentite , benleonardite , chenguodaite , cervelleite , empressite , hessite , naumannite , tsnigriite and supportite, the "argentite-naumannite group" with the system no. II / B.05 .
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 acanthite to the class of "sulfides and sulfosalts" and there in the department of "metal sulfides, M: S> 1: 1 (mainly 2: 1) ”. However, this section is further subdivided according to the type of cations involved , so that the mineral can be found in accordance with its composition in the subdivision "with copper (Cu), silver (Ag), gold (Au)", where it can only be found together with Argentite forms the unnamed group 2.BA.30a .
The systematics of minerals according to Dana also assigns acanthite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is the namesake of the "Akanthitgruppe" with the system no. 02.04.01 and the other members naumannite and aguilarite can be found within the subsection " Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 2: 1 ".
Crystal structure
Acanthite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a = 4.23 Å ; b = 6.93 Å; c = 7.86 Å and β = 99.6 ° as well as 4 formula units per unit cell .
Modifications and varieties
Acanthite is the monoclinic, low-temperature modification of the cubic argentite , so it changes its crystal system when it cools below 173 ° C. However, it often retains the outer crystal form of argentite ( paramorphosis ).
Education and Locations
Akanthit formed hydrothermally in silver ore - courses . Accompanying minerals include argentite, silver, prostite , pyrargyrite and others as well as galena , in which acanthite is often included.
Acanthite has been found at around 2100 sites worldwide (as of 2010).
In Germany, the mineral was found in the Black Forest in Baden-Württemberg, among other places ; in the Fichtelgebirge , Bavarian and Upper Palatinate Forest in Bavaria; in the Odenwald and Taunus in Hesse; in the Harz in Lower Saxony; at several sites in North Rhine-Westphalia ; in the Eifel and on the Hunsrück in Rhineland-Palatinate; in Saarland ; in Saxony-Anhalt ; on Annaberg , Schneeberg and many other areas of Saxony as well as in Thuringia .
In Austria, acanthite was found mainly in the regions of Carinthia , Lower Austria , Salzburg , Styria and Tyrol .
In Switzerland, the mineral has so far only been found at Miglieglia in Ticino, Binntal and Lötschental in the canton of Valais.
Other locations 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 US Virgin Islands , the United Kingdom (Great Britain) and the United States of America (USA).
Acanthite was also found in rock samples from the Mid-Atlantic Ridge and the Moon , which the Luna 24 mission brought back.
use
Acanthite is one of the most important raw materials for the extraction of silver .
See also
literature
- Martin Okrusch, Siegfried Matthes: Mineralogy: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 .
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 421 .
Web links
- Mineral Atlas: Acanthite (Wiki)
- Adolf Kenngott: Also the acanthite, a new species in the family of the silver luster . In: Annals of Physics and Chemistry (Fifth Volume). Hrs: JC Poggendorff, Verlag von Johann Ambrosius Barth, Leipzig 1855, p.465 ff. (PDF 187.5 kB)
- Handbook of Mineralogy - Acanthite (English, PDF 62.4 kB)
- Webmineral - Acanthite (English)
Individual evidence
- ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 64 .
- ↑ a b List of localities for Akanhit in the Mineralienatlas and Mindat