Voltaite
| Voltaite | |
|---|---|
 |
|
| General and classification | |
| other names |
|
| chemical formula | K 2 Fe 5 2+ Fe 3 3+ Al [SO 4 ] 12 · 18H 2 O |
|
Mineral class (and possibly department) |
Sulphates (selenates, tellurates, chromates, molybdates, tungstates) |
|
System no. to Strunz and to Dana |
7.CC.25 ( 8th edition : VI / C.14) 09/29/01/01 |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | cubic hexakisoctahedral; 4 / m 3 2 / m |
| Space group | Fd 3 c (No. 228) |
| Lattice parameters | a = 27.25 Å |
| Formula units | Z = 16 |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | measured: 2.645 (synthetic); calculated: 2.663 |
| Cleavage | no |
| Break ; Tenacity | shell-like, brittle |
| colour | greenish black, black, dark olive green; light green to olive green in transmitted light |
| Line color | gray-green |
| transparency | opaque, translucent in thin layers |
| shine | Resin gloss |
| Crystal optics | |
| Refractive index | n = 1.593 to 1.608 |
| Birefringence | 0.000 (isotropic) |
| Optical character | usually biaxial in sectors abnormally |
| Other properties | |
| Chemical behavior | water-soluble (forms acidic, lemon-yellow solution), acid-soluble |
Voltaite is a rarely occurring mineral from the mineral class of " sulfates ( and relatives )". It crystallizes in the cubic crystal system with the chemical composition K 2 Fe 5 2+ Fe 3 3+ Al [SO 4 ] 12 · 18H 2 O and is therefore chemically a water-containing potassium - iron - aluminum sulfate.
Voltaite mostly develops octahedral or dodecahedral crystals and combinations up to about two centimeters in size, but also granular to massive mineral aggregates and efflorescence of dark green to black color with gray-green streak color .
The mineral is usually opaque and only thin layers of translucent green. The brittle crystals break like glass and have a resin-like sheen on their surfaces . With a Mohs hardness of 3, voltaite, like the reference mineral calcite, is one of the medium-hard minerals that can be scratched with a copper coin.
Etymology and history
Voltaite was first discovered on the fumaroles of the solfatara near Pozzuoli in the Italian region of Campania.
A first mention of the mineral comes from Scipione Breislak , who describes it in 1792 in an "Essai minerologique sur la solfatare de Puozzole". However, it was not until 1841 that Voltaite was clearly analyzed by Arcangelo Scacchi , who named the mineral after Alessandro Volta in order to honor his achievements in the fields of physics and electricity.
A mineral from Kremnitz ( Kremnica ) in Slovakia described by A. Paulinyi in 1867 and named by him as pettkoite was identified as voltaite after examination by Gustav Tschermak . The secondary name Pettkoit therefore had to be withdrawn.
A dark green mineral from Baia Sprie (Romania), initially thought to be a tellurium analogue of voltaite, was discovered in 1965 by Manilici et al. described and referred to as Monsmedit . However, recent studies have shown that the mineral is identical to voltaite, whereupon the name Monsmedite was discredited.
classification
In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the voltaite belonged to the mineral class of "sulfates, selenates, tellurates, chromates, molybdates, wolframates" and there to the department of "hydrous sulfates without foreign anions ", where it belongs together with alum (K) (formerly potash alum ), alum (N) (formerly soda alum ), Lanmuchangit , Lonecreekit , Pertlikit , Tschermigit and Zincovoltait the "alum group" with the system no. VI / C.14 .
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 voltaite to the category of "sulfates (selenates, etc.) without additional anions, with H 2 O". This is, however, further subdivided according to the size of the cations involved , so that the mineral can be found in the sub-section “With medium-sized and large cations” according to its composition, where it is named after the “Voltaite group” with the system no. 7.CC.25 and the other members Pertlikit and Zincovoltait.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns voltaite to the class of "sulfates, chromates and molybdates" and there in the department of "water-containing acids and sulfates". Here he is also the namesake of the "Voltaitgruppe" with the system no. 09/29/01 and the other members Pertlikit and Zincovoltait can be found within the sub-section of " Water-based acids and sulfates with various formulas ".
Crystal structure
Voltaite crystallizes cubically in the space group Fd 3 c (space group no. 228) with the lattice parameter a = 27.25 Å and 16 formula units per unit cell .
properties
In water, voltaite decomposes and forms an acidic solution with a lemon-yellow residue. It is also soluble in acids.
Education and Locations
Voltait formed secondarily as a conversion product in pyrite - deposits , primarily under arid conditions , where he may occur secondarily due to mining activities. Accompanying minerals include alunogen , botryogen , copiapit , coquimbit , goldichite , halotrichite , hexahydrite , jarosite , krausite , melanterite , metavoltine , pickeringite , rhomboclase and romanite .
As a rare mineral formation, Volaite could only be detected at a few sites, although around 100 sites are known to date (as of 2015). In addition to its type locality "Solfatara di Pozzuoli", the mineral was also found in Italy in the "Atrio del Cavallo" between Vesuvius and Monte Somma, in several places on the island of Vulcano (Sicily) and in the Campiano ( Montieri ), Pereta , Cape Calamita ( Capoliveri ) and Cava del Ferro ( Fornovolasco ) in Tuscany .
In Germany, voltaite has so far been found in the Clara mine near Oberwolfach (Baden-Württemberg), the “Bayerland” mine near Pfaffenreuth ( Leonberg (Upper Palatinate) ), on the Rammelsberg (Lower Saxony), in the Anna , Julia mines in North Rhine-Westphalia and Auguste Victoria , the “Grube Einheit” near Elbingerode (Saxony-Anhalt), the “ Carola ” and “Willi Agatz” mines near Dresden (Saxony) and formerly also in the tailings dumps near Ronneburg (Thuringia).
In Austria, Voltait has so far only been found in Styria, more precisely near Zangtal in the lignite warehouse of Köflach - Voitsberg and in the Spitzmühle quarry near Leutschach .
The only previously known site in Switzerland is Les Valettes on Mont Chemin near Martigny in the canton of Valais.
Other locations include Argentina, Australia, Belgium, Bolivia, Chile, China, Greece, France, Iran, Japan, Canada, Mexico, Poland, Slovakia, Spain, Tajikistan, Czech Republic, Hungary, the United States of America (USA) and Cyprus.
See also
literature
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 609 (first edition: 1891).
Web links
- Mineral Atlas: Voltaite (Wiki)
- RRUFF Database-of-Raman-spectroscopy - Voltaite (English)
- American-Mineralogist-Crystal-Structure-Database - Voltaite (English)
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 388 .
- ↑ Webmineral - Volaite (English)
- ↑ a b c d e f g Voltaite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 66 kB ; accessed on September 24, 2017]).
- ↑ Mindat - Voltaiteg (English)
- ^ J. Blaas: Contributions to the knowledge of natural water-containing double sulfates . In: Session reports of the mathematical and natural science class of the Imperial Academy of Sciences . 87 (Department 1). Vienna 1883, p. 143–155 ( rruff.info [PDF; 989 kB ; retrieved on September 24, 2017] Presented at the February 1, 1883 session).
- ↑ Gustav Tschermak : The spread of olivine in the rock types . In: Negotiations of the Imperial and Royal Geological Institute . Vienna 1867, p. 160 ( geologie.ac.at [PDF; 82 kB ]).
- ↑ Zdenek Johan, Gheorghe Udubasa, Josef Zemann: "Monsmedite" a discredited potassium thallium sulphate mineral from Baia Sprie and its identity with voltaite: The state of the art . In: New Yearbook for Mineralogy - Treatises . tape 186 , no. 1 . Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 2009, p. 63-66 , doi : 10.1127 / 0077-7757 / 2009/0137 .
- ↑ Mindat - Number of localities for Voltait
- ↑ Find location list for voltaite at the Mineralienatlas and at Mindat