Asbecasite

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Asbecasite
Asbecasite-188175.jpg
Tabular asbecasite crystal from the Wannigletscher-Scherbadung area (Monte Cervandone), Kriegalptal, Binntal , Valais , Switzerland (field of view: 15 mm)
General and classification
other names

IMA 1965-037

chemical formula
  • Ca 3 (Ti, Sn 4+ ) Be 2 (AsO 3 ) 6 (SiO 4 ) 2
  • Ca 3 (Ti, Sn 4+ ) As 3+ 6 Si 2 Be 2 O 20
  • Ca 3 TiAs 6 Be 2 Si 2 O 20
  • Ca 3 (Be, B) 2 (Ti, Sn, Fe) As 3+ 6 Si 2 O 20
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.JB.30 ( 8th edition : VIII / B.11)
45.01.03.01
Similar minerals Wulfenite
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3  2 / m
Space group P 3 c 1 (No. 165)Template: room group / 165
Lattice parameters a  = 8.318  Å ; c  = 15.264 Å
Formula units Z  = 2
Frequent crystal faces {01 1 2}, {0001}
Physical Properties
Mohs hardness 6.5 to 7
Density (g / cm 3 ) 3.70 (measured); 3.71 (calculated)
Cleavage very perfect after the rhombohedron {01 1 2}
Break ; Tenacity clamshell; brittle
colour lemon yellow, light yellow, flax yellow, orange
Line color pale yellow
transparency transparent
shine "High", glass gloss, resin gloss
Crystal optics
Refractive indices n ω  = 1.830
n ε  = 1.860
Birefringence δ = 0.030
Optical character uniaxial negative, abnormal biaxial
Axis angle 2V = 0 ° to 17 °
Pleochroism unavailable
Other properties
Chemical behavior Slightly soluble in hydrochloric acid, potentially unstable in oxalic acid

Asbecasite is a very rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the trigonal crystal system with the idealized chemical composition Ca 3 (Ti, Sn 4+ ) Be 2 (AsO 3 ) 6 (SiO 4 ) 2 and is therefore chemically a calcium - titanium - beryllium - arsenite - silicate , more precisely an arsenite with additional anions and without additional H 2 O.

Asbecasite mainly forms, after the base pinacoid, thin or thick tabular, rhombohedral crystals with a maximum size of 2 cm, which in most cases have grown together to form radial, fan-shaped aggregates .

The type locality of the Asbecasit is the Wannigletscher area - west flank of the Scherbadung (Monte Cervandone) ( coordinates of the Wannigletscher-Scherbadung area ) in the Kriegalptal, a side valley of the Binntal in the canton of Valais in Switzerland .

Etymology and history

Asbecasite accompanied by chlorite and fine Schörl or Dravit needles. Wannigletscher-Scherbadung area, Kriegalptal, Binntal, Valais, Switzerland (size: 6.5 cm × 4.8 cm × 2.6 cm)

On September 16, 1963, the Swiss mineralogist and later a professor at the thought of Mineralogy and Petrography Institute of the University of Basel Stefan Grasses in crevices of the two-mica gneisses of after Monteleone named Monte Leone ceiling in the area Wannigletscher - Scherbadung two unknown minerals, one of which Canary , 0.5 mm large plates and the other forms up to 3 cm large, dark brown cubic crystals with rough surfaces. After the first chemical and X-ray diffractometric investigations, both turned out to be new minerals. This work was related to investigations to clarify the origin of the arsenic-containing solutions that were involved in the formation of the arsenic sulfosalts in the Lengenbach mine .

After intensive further research, the lemon-yellow tabular mineral was submitted to the International Mineralogical Association (IMA), which recognized it as a new mineral in 1965. In 1966, the first scientific description of this mineral was carried out by Stefan Grasses in the Swiss science magazine Swiss mineralogical and petrographic messages as Asbecasit ( English Asbecasite ). The author named it AsBeCaSi-t after the symbols of the most important chemical elements involved in the composition of the new mineral arsenic (As), beryllium (Be), calcium (Ca) and silicon (Si).

The type material for asbecasite (holotype) is stored under catalog number SG750 in the collection of the Natural History Museum Basel , Switzerland. Further types can be found in the collections of the Muséum national d'histoire naturelle in Paris , France (collection number 180.40), the Natural History Museum in London , United Kingdom (collection number 1966,222), and the National Museum of Natural History in Washington, DC , USA (collection number 143117).

The other finds are initially only made in Italy and Switzerland. In 1985, the Italian amateur mineralogist Francesco Saverio Stoppani found fan-shaped aggregates of thin-plate asbecasite crystals while working on a large, thermometamorphically influenced ejecta in "Tre Croci" near Vetralla , Lago di Vico volcanic complex , Viterbo province , Latium region , Italy . From the eastern flank on the Italian side of the Scherbadung, here called “Monte Cervandone”, asbecasite finds from quartz veins in the area of ​​the northeast flank of the “Pizzo Bandiera” were reported. Further asbecasite finds come from pegmatite dikes in the central area of ​​Monte Cervandone.

In 1986, the place of Le Locle NE originating spotlight Alexandre Skrapits in "Gorb" in the "Lärcheltini zone", also in Switzerland's Binn Valley, in an old anatase - divide tabular Asbecasit crystals several millimeters in diameter. In 1990, asbecasite was found in the Mättital , another side valley of the Binntal, in the form of pale yellow crystals and flax-yellow powdery masses. The Dutch collector Ate van der Burgt was able to locate asbecasite in the form of deposits up to 1 cm in size and up to 2 mm in size crystals on the Hillehorn north-east slope in the “Chummibort” region, which is also in the Binn valley.

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the asbecasite belonged to the mineral class of "silicates and germanates" and there to the department of " island silicates with non- tetrahedral anions (Neso-subsilicates)", where it belonged together with Dixenit , Kraisslit , Mcgovernit and Turtmannit formed the unnamed group VIII / B.11 .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns asbecasite to the class of "oxides and hydroxides", but in the newly defined division of "arsenites, antimonites, bismuthites" , Sulphites, Selenites and Tellurites ”. This is further subdivided according to the possible presence of crystal water and / or additional anions , so that the mineral can be found according to its composition in the sub-section “Arsenite, Antimonide, Bismutide, without additional anions, without H 2 O”, where it can be found as the only member is the unnamed group 4.JB.30 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns asbecasite to the class of "phosphates, arsenates and vanadates" and there to the category of "acids and normal antimonites, arsenites and phosphites". Here he is to be found as the only member in the unnamed group 45.01.03 within the sub-section “ Acid and normal antimonites, arsenites and phosphites with various formulas ”.

Chemism

A microprobe analysis of Asbecasit of the type locality yielded 12.3% SiO 2 ; 6.3% TiO 2 ; 2.1% SnO 2 ; 1.2% Al 2 O 3 ; 58.7% As 2 O 3 ; 1.0% Tl 2 O 3 ; 2.3% BeO; 15.4% CaO (total 99.3%), which gives the empirical formula Ca 2.67 (Ti 0.67 Sn 0.13 Tl 0.04 ) Σ = 0.84 As 3+ based on 20 oxygen atoms 6.67 Si 2.00 Al 0.27 Be 1.00 O 20 and calculate Ca 2 Si 1.5 Be 0.75 Ti 0.5 Al 0.2 Sn 0.1 Tl 0.03 (AsO 3 ) 5 can be idealized. This ideal formula requires contents of 11.43% SiO 2 ; 5.07% TiO 2 ; 1.92% SnO 2 ; 1.29% Al 2 O 3 ; 62.78% As 2 O 3 ; 0.89% Tl 2 O 3 ; 2.38% BeO; 14.24% CaO (total 100.00%).

On an asbecasite variety containing antimony from “Tre Croci” near Vetralla, a composition with 11.34% SiO 2 ; 3.90% BeO; 1.02% FeO; 0.42% Al 2 O 3 ; 0.53% B 2 O 3 ; 51.95% As 2 O 3 ; 7.39% Sb 2 O 3 ; 5.68% TiO 2 ; 0.23% SnO 2 ; 0.04% ThO 2 ; 15.69% CaO (total 98.19%) determined. Based on 20 oxygen atoms, 14 metal ions and a completely anhydrous composition, the empirical formula (Ca 2.989 Th 0.002 ) Σ = 2.991 (Ti 0.760 Sn 0.016 Fe 0.152 ) Σ = 0.928 (As 3+ 5.611 Sb 0.542 ) Σ = 6.153 Si 2.017 (Be 1.666 B 0.163 Al 0.088 ) Σ = 1.917 O 19.995 .

The combination of elements Ca – Ti – Be – As – Si is unique among the currently known minerals; so there are no minerals with a chemical composition similar to that of asbecasite.

Crystal structure

Crystal structure of asbecasite in cation-centered polyhedral representation and standard orientation. Color legend:
__ Ca __ As __ Ti __ Si __ Be __ O
Crystal structure of asbecasite in a cation-centered polyhedral representation. Direction of view along [001]. Color legend:
__ Ca __ As __ Ti __ Si __ Be __ O

Asbecasite crystallizes in the trigonal crystal system in the space group P 3 c 1 (space group no. 165) with the lattice parameters a = 8.318  Å and c = 15.264 Å as well as two formula units per unit cell . Template: room group / 165

The crystal structure of the asbecasite consists of two different layers. Layer A consists of [BeO 4 ] and [SiO 4 ] tetrahedra , which are connected to one another via the common O4 atom, as well as trigonal [AsO 3 ] pyramids at the top and bottom of the layer. Layer B is made up of [TiO 6 ] octahedra and tetragonal (square) [CaO 8 ] antiprisms . The antiprisms are only linked via the corners, but each antiprism has a common edge with a [TiO 6 ] octahedron. Layers B extend parallel (0001) and alternate with layers A, so that a stacking sequence ... AABAAB ... is created. The first determination of the crystal structure of the asbecasite was presented in 1969 by Elio Cannillo and co-workers.

properties

Crystal drawing of a thick tabular asbecasite crystal

morphology

Asbecasite is often found in the form of grown crystals in areas rich in biotite in fissures in gneiss or grown in calcite . It forms rhombohedral crystals with a maximum size of 2 cm, which are thin or thick tabular according to the basic pinacoid {0001}. The only other surface shape is the negative rhombohedron {01 1 2}. Often the crystals are hexagonal with sloping rhombohedral surfaces, occasionally isometric crystals are also found. In most cases the rhombohedral crystals come together to form radial, fan-shaped aggregates. In addition to being in the form of crystals, asbecasite also occurs in powdery masses and coatings of several square centimeters in size.

The antimony-containing asbecasites of “Tre Croci” form book-shaped or fan-shaped aggregates of tiny idiomorphic plate-like crystals with a pseudo-hexagonal habit.

physical and chemical properties

Asbecasite crystals are lemon yellow, light yellow, flax yellow, orange or yellowish-olive green, while the color of the antimony-containing asbecasite of “Tre Croci” is described as “custard yellow”, i.e. yellow like vanilla pudding. Stefan Graeser already points out that the rich dark yellow color of the fresh asbecasite changes to beige or whitish to greenish yellow when weathering or decomposition begins. The streak color of the asbecasite crystals, however, is given as pale yellow. The surfaces of the transparent crystals show a high gloss , which was specified as glass gloss or resin gloss. Asbecasite has a very high light refraction (n ε  = 1.860; n ω  = 1.830) and a moderately high birefringence (δ = 0.030) , corresponding to its strong gloss . In transmitted light, the mineral is light yellow and does not show any pleochroism .

Asbecasite has a very perfect cleavage after the rhombohedron {01 1 2} Due to its brittleness it breaks like quartz , whereby the break surfaces are formed like a shell. The mineral has a Mohs hardness of 6.5 to 7 and is one of the medium-hard to hard minerals that scratch window glass just as well as the reference mineral quartz (hardness 7) . The measured density for asbecasite is 3.70 g / cm³, the calculated density is 3.71 g / cm³. Asbecasit is neither in the long term nor in the short wavelength UV light , a fluorescent .

Asbecasite is sparingly soluble in hydrochloric acid , HCl, and potentially unstable in oxalic acid .

Education and Locations

Asbecasite is a secondary mineral that was able to form due to an arsenic anomaly in the two mica gneisses on the Wanni Glacier. A pre-alpine ( Variscan ?) Cu-As mineralization with tennantite and chalcopyrite located in the gneiss of the Monte Leone Nappe was sunk during the unfolding of the Alps and was overprinted by an amphibolite facial regional metamorphosis. Hot hydrothermal solutions partially dissolved the ores again. The arsenic-containing ore minerals of the primary mineralization in the Monte Leone Nappe reacted with a Cl - and F - -rich CO 2 -H 2 O fluid, the origin of which is traced back to the Mesozoic metasediments in the Monte Leone Nappe . The arsenic oxidized and was probably transported as H 3 AsO 3 0 complexes. These solutions became heavily enriched with arsenic and migrated to the north, probably along north-east-south-west trending fault systems. The resulting cooling led to supersaturation and consequently to the crystallization of arsenic-rich minerals. Owing to the lower oxygen content in the depths, these were often arsenites which, in contrast to arsenates with the functional [As 5+ O 4 ] group, contain the lower oxygen functional [As 3+ O 3 ] group. Asbecasit provides next Cafarsit , Fetiasit and Cervandonit- (Ce) is one of these rare naturally occurring arsenite minerals.

In addition to alpine-type fissures, asbecasite has also been found in volcanic ejecta (“Tre Croci”), pegmatites (“Monte Cervandone”, “Tennvatn pegmatite”) and quartz veins (“Monte Cervandone”). It is very remarkable that a mineral with such a complex chemical composition can be formed in so many different ways.

Typical accompanying minerals of asbecasite are chlorite ( rhipidolite ), quartz, tilasite , fluorite , magnetite and cafarsite (Wannigletscher) as well as tennantite, bournonite , cafarsite, cervandonite (Ce), fetiasite and mimetesite (larcheltini). In the type publication, magnetite, hematite , titanite , apatite , anatase, malachite , azurite , a pale ore ( tennantite ) and molybdenite (polytype molybdenite-6 H ) are given as paragenesis minerals of asbecasite . Asbecasite is found on the “Gischigletscher” accompanied by metazeunerite . Asbecasite and cafarsite can be grown together directly. In the ejections of “Tre Croci” the asbecasite sits between sanidine crystals and is accompanied by biotite and augite and the accessory minerals magnetite, titanite and sodalite . Danburit , Vonsenit , thorite , Betafit , baddeleyite , Th -rich Ekanit , Uranthorianit , zircon and Kryptomelan may also be present. In the Norwegian "Tennvatn pegmatite" the Asbecasit between finds albite -self the variety Cleavelandit and is of Amazonit , muscovite , hematite, apatite , Stilbite , zircon, monazite , cassiterite , Chernovit- (Y ) and a representative of the pyrochlore group Upper accompanied .

As a very rare mineral formation, the asbecasite could so far (as of 2019) only be described from about ten sites. The type locality for asbecasite is the Wannigletscher area - western flank of the Scherbadung in the Kriegalptal, a tributary valley of the Binntal , Valais , Switzerland that extends to the southeast . The type locality is thus on the Swiss side of the mountain Scherbadung - Monte Cervandone.

There are a number of other sites, the majority of which are also in the closer or further vicinity of the shear bath - Monte Cervandone and also go back to the remobilization of the pre-alpine Cu-As mineralization described above:

Sites for asbecasite from Germany and Austria are therefore unknown.

use

Asbecasite is only of interest to mineral collectors due to its rarity.

See also

literature

  • Stefan Graeser: Asbecasite and Cafarsite, two new minerals from the Binnatal (canton of Valais) . In: Swiss mineralogical and petrographic messages . tape 46 , no. 2 , 1966, p. 367–375 , doi : 10.5169 / seals-36131 ( e-periodica.ch [PDF; 11.1 MB ; accessed on January 20, 2019]).
  • Giancarlo Della Ventura, Adriana Maras, Annibale Mottana, Gian Carlo Parodi, Michele Sacerdoti, Francesco Saverio Stoppani: Antimonian asbecasite in a syenitic ejectum within the Vico pyroclastic rocks (Roman potassic province) . In: Rendiconti Accademia dei Lincei, Classe di Scienze Fisiche, Matematiche e Naturali Ser. 9 . tape 2 , 1991, p. 387–394 , doi : 10.1007 / BF03000993 (English, link.springer.com [PDF; 418 kB ; accessed on January 20, 2019]).
  • Asbecasite . 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; 72 kB ; accessed on January 20, 2019]).

Web links

Commons : Asbecasite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m n Asbecasite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 30, 2019 .
  2. ↑ a b c d e Asbecasite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 72  kB ; accessed on January 20, 2019]).
  3. ↑ Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: July 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, July 2019, accessed August 28, 2019 .
  4. ^ 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.  267 .
  5. ^ Philippe Roth: Minerals first discovered in Switzerland and minerals named after Swiss individuals . 1st edition. Kristallografik Verlag, Achberg 2007, ISBN 978-3-9807561-8-1 , p. 36–37 (English, limited preview in Google Book Search).
  6. ↑ a b c d e f Stefan Graeser: Wannigletscher and Conca Cervandone . In: Lapis . tape 20 , no. 7-8 , 1995, pp. 41-64 .
  7. ↑ a b Stefan Graeser, Aldo G. Roggiani: Occurrence and genesis of rare arsenate and phosphate minerals around Pizzo Cervandone, Italy / Switzerland . In: Rendiconti della Società Italiana di Mineralogia e Petrologia . tape XXXII , no. 1 , 1976, p. 279–288 (English, rruff.info [PDF; 1.4 MB ; accessed on January 20, 2019]).
  8. ↑ a b c d e f Michele Sacerdoti, Gian Carlo Parodi, Annibale Mottana, Adriana Maras, Giancarlo Della Ventura: Asbecasite: crystal structure refinement and crystal chemistry . In: Mineralogical Magazine . tape 57 , no. 387 , 1993, pp. 315–322 , doi : 10.1180 / minmag.1993.057.387.14 (English, rruff.info [PDF; 455 kB ; accessed on January 20, 2019]).
  9. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa Stefan Graeser: Asbecasite and cafarsite, two new minerals from the Binnatal (canton of Valais) . In: Swiss mineralogical and petrographic messages . tape 46 , no. 2 , 1966, p. 367–375 , doi : 10.5169 / seals-36131 ( e-periodica.ch [PDF; 11.1 MB ; accessed on January 20, 2019]).
  10. ↑ a b c d e Stefan Graeser: New: Arsenic minerals from the Lärcheltini zone . In: Lapis . tape 20 , no. 7-8 , 1995, pp. 36-40 .
  11. ↑ a b c d Michael Krzemnicki, Stefan Graeser: Das Mättital . In: Lapis . tape 20 , no. 7-8 , 1995, pp. 68-71 .
  12. ↑ a b c d e f Hans Anton Stalder, Albert Wagner, Stefan Graeser, Peter Stuker: Mineralienlexikon der Schweiz . 1st edition. Wepf & Co., Basel 1998, ISBN 978-3-85977-200-7 , p. 54 .
  13. ↑ a b Rudolf Duthaler, Stefan Weiß: Clean, prepare and store minerals. The workbook for the collector . 1st edition. Christian Weise Verlag, Munich 2008, ISBN 978-3-921656-70-9 , p. 160 .
  14. ↑ Stefan Grasses: Cherbadung September 1963: The discovery of the first arsenite zone . In: Lapis . tape 20 , no. 7-8 , 1995, pp. 33-35 .
  15. ↑ Catalog of Type Mineral Specimens - A. (PDF 84 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 28, 2019 .
  16. ↑ a b c d e f Giancarlo Della Ventura, Adriana Maras, Annibale Mottana, Gian Carlo Parodi, Michele Sacerdoti, Francesco Saverio Stoppani: Antimonian asbecasite in a syenitic ejectum within the Vico pyroclastic rocks (Roman potassic province) . In: Rendiconti Accademia dei Lincei, Classe di Scienze Fisiche, Matematiche e Naturali Ser. 9 . tape 2 , no. 4 , 1991, pp. 371–378 , doi : 10.1007 / BF03000993 (English, link.springer.com [PDF; 418 kB ; accessed on January 20, 2019]).
  17. ^ A b c Claudio Albertini: L'Alpe Devero ed i suoi minerali . 1st edition. Edizioni Grafica PGA, Dormelletto (Novara) 1991, p. 1-299 (Italian).
  18. ↑ a b c d e f Alessandro Guastoni, Federico Pezzotta, Pietro Vignola: Characterization and genetic inferences of arsenates, sulfates and vanadates of Fe, Cu, Pb, Zn from Mount Cervandone (Western Alps, Italy) . In: Periodico di Mineralogia . tape 75 , no. 2–3 , 2006, pp. 141–150 (English, researchgate.net [PDF; 341 kB ; accessed on January 20, 2019]).
  19. ↑ a b c Stephane Cuchet, Ate van der Burgt, Nicolas Meisser: Chummibort, a new site for arsenic minerals in the Binn valley . In: Swiss emitters . tape 2005 , no. 2 , 2005, p. 19-29 .
  20. ↑ Elio Cannillo, Giuseppe Giuseppetti, Carla Tadini: The crystal structure of asbecasite . In: Rendiconti Atti Accademia Nazionale dei Lincei, Classe di Scienze Fisiche Matematiche e Naturali, Ser. 8 . tape 46 , no. 2 , 1967, p. 457-467 (English).
  21. ↑ a b c d Astrid Haugen, Hans Vidar Ellingsen: Asbecasite - a new find in Norway . In: Mineral World . tape 5 , no. 2 , 1994, p. 14 .
  22. ↑ Michael Krzemnicki: As-Bi mineralizations in the Mte Leone Nappe of the Mattitales, Binntal region (CH) . In: Communications from the Austrian Mineralogical Society . tape 137 , 1992, pp. 163–164 ( opac.geologie.ac.at [PDF; 6.1 MB ; accessed on January 20, 2019]).
  23. ↑ a b c Hans Vidar Ellingsen, Tomas Andersen, Astrid Haugen: Nye mineraler fra amazonittpegmatitten ved Tennvatn, Nordland . In: Norsk Bergverksmuseum Skrift . tape 17 , 1994, p. 52–58 ( nags.net [PDF; 10.3 MB ; accessed on January 20, 2019]).
  24. ↑ Localities for Asbecasite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 30, 2019 .
  25. ↑ Find location list for asbecasite in the Mineralienatlas and Mindat (accessed on January 15, 2019)
  26. ^ Stefan Graeser, Hans Schwander, Francesco Demartin, Carlo M. Gramaccioli, Tullio Pilati, Eric Reusser: Fetiasite (Fe 2+ , Fe 3+ , Ti) 3 O 2 [As 2 O 5 ], a new arsenite mineral: its description and structure determination . In: The American Mineralogist . tape 79 , 1994, pp. 996–1002 (English, rruff.info [PDF; 867 kB ; accessed on January 20, 2019]).