Scapolite group

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Scapolite group
Scapolite - Badakhshan, Afghanistan.jpg
Two purple scapolites on bedrock with unknown green crystals
General and classification
chemical formula (Na, Ca) 4 (Si, Al) 12 O 24 (Cl, CO 3 )
Mineral class
(and possibly department) 		Silicates
System no. to Strunz
and to Dana 		9.FB.15
76.03.01.00
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol tetragonal-dipyramidal; 4 / m
Space group I 4 / m (No. 87) and P 4 2 / n (No. 86)Template: room group / 87Template: room group / 86
Formula units Z  = 2
Frequent crystal faces {100}, {110}, {101}, {211}
Twinning no
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) 2.50 to 2.80
Cleavage clearly after {100}, {110}
Break ; Tenacity uneven to scalloped
colour colorless, white, gray, pink, violet, blue, yellow, brown
Line color White
transparency transparent to opaque
shine Glass gloss
Crystal optics
Refractive index n  = 1.532 to 1.600
Birefringence δ = 0.018 to 0.044
Optical character uniaxial negative
Other properties
Special features orange to light yellow fluorescence under UV light

The scapolite group , also known obsolete as wernerite , is a group of tetragonal framework aluminosilicates with the general composition:

D 4 [T 4 O 8 ] 3 (X, Z) 2 / v ; v = 1, 2 In this formula:

  • D: Large cations surrounded by 9 or more anions: Na + , Ca 2+ , K + , Sr 2+ , Ba 2+ , Fe 2+
  • T: Small cations that are tetrahedrally surrounded by 4 anions: Si 4+ , Al 3+
  • O: oxygen
  • X: Monatomic anions: Cl - , Br -
  • Z: Polyatomic anions: CO 3 , SO 4 , HSO 4 , H CO 3 , OH, H 2 O
  • v: valence (charge) of the anions X and Z

The scapolite group includes the minerals

which form a gapless row of mixed crystals .

The abbreviation scapolite is mostly used for a mixed crystal of the marialite – mejonite series.

The crystals, sometimes over 1 m in size, are prismatically stretched along the crystallographic c-axis. Their shape is dominated by the prism surfaces {100} and {110}. The prisms are mainly limited by the pyramid surfaces {101}. There is often a surface striation in the longitudinal direction on the prismatic surfaces.

Etymology and history

The name scapolite is derived from the Greek word skapos (stick) and lithos (stone).

The name scapolite was introduced in 1800 by José Bonifácio de Andrada e Silva . Wernerite is also described in the same work. For decades, both names were used in parallel, alternately as group and variety names, until the CNMMN (Commission on New Minerals and Mineral Names) rejected the name Wernerite in 1997 and set scapolite as the group name.

classification

According to Strunz's system (9th edition), the scapolite group (9.FB.15) belongs to mineral class 9 (silicates), division of structural silicates without zeolitic H 2 O (F) with other anions (B).

According to Dana's systematics, the scapolite group (76.03.01) belongs to the class of structural silicates with SI-Al framework (76) with other Be / Al / Si framework structures (03).

Crystal structure

Scapolites crystallize tetragonally in the space group I 4 / m (space group no. 87) and P 4 2 / n (no. 86) with two formula units per unit cell . Marialite- and meionite-rich scapolites crystallize in the space group I 4 / m (No. 87) whereas the mixed crystal structure has the space group P 4 2 / n (No. 86) . Accordingly, the scapolite group can be divided into three isomorphic series: Template: room group / 87Template: room group / 86Template: room group / 87Template: room group / 86

  • 9.0> Si> 8.4: Marialite rich in scapolites
  • 8.4> Si> 7.3: intermediate scapolites
  • 7.3> Si> 6.0: Meionite rich scapolites

Structurally, these series differ primarily in the distribution of Al and Si on the various lattice positions in the aluminosilicate framework.

Si and Al are surrounded by four oxygen in such a way that the oxygen lies on the corners of a tetrahedron with the Si or Al cation in the center (tetrahedral coordination). These (Si, Al) O 4 tetrahedra are linked to one another over all four corners to form a three-dimensional framework (framework silicate). This framework is made up of rings of 4 and 5 (Si, Al) O 4 tetrahedra, which, like in zeolites , enclose larger cavities. In each of these cavities there is an (X, Z) anion (Cl, CO 3 ) and 4 D cations (Na, Ca).

The large D cations in the aluminosilicate cavities are surrounded by 7 oxygen and one (X, Z) anion.

properties

Scapolite is colorless in itself, but it can be colored pink, purple, blue, yellow or brown due to traces of coloring elements. Inclusions of graphite lead to a gray to black color. The stroke color is white. The crystals are transparent to opaque and cloudy with a glass luster. The density is 2.50 - 2.80 g / cm 3 . The hardness of scapolite is comparable to that of feldspars ( Mohs hardness 5–6).

  • Color variations of scapolite

  • colorless (Madagascar)

  • yellow (Tanzania)

  • purple (Afghanistan)

  • golden brown (Tanzania)

  • gray (Canada)

Scapolites fluoresce orange to bright yellow and, more rarely, red in UV light.

  • Wernerite fluorescence

Varieties

Dipyr (also melting stone ) is a variety of scapolite rich in sodium and chlorine . Even the Mizzonit is a solid solution of Skapolithreihe, but is defined as sodium-rich Mejonit.

Gabbronite is the term for an insufficiently described mineral, which can be either scapolite or nepheline .

Education and Locations

Scapolite is found worldwide in contact metamorphic calcium silicate rocks ( skarn ) as well as metamorphic basic rocks (metagabbros, metadiorite) and gneisses.

In gneisses and metabasites, scapolite is formed when feldspars react with NaCl-rich solutions and occurs together with plagioclase , hornblende , clinopyroxene .

In skarn deposits, scapolite is found associated with calcite , diopside , epidote , phlogopite , tremolite , garnet , vesuvianite , wollastonite , titanite , potassium feldspar , fluorite , and pyrite .

Sulphate-rich scapolites are found in garnet granulites of the lower crust and the upper mantle . There they occur together with plagioclase , Ca amphiboles , clinopyroxene , pyrope-rich garnets and spinel . The mineral structure suggests that scapolites of these deposits were not formed secondary by conversion of feldspars, but were crystallized directly from hydrous alkaline basalt magmas.

Furthermore, scapolite could be detected in meteorites ( chondrite ).

use

Colorless scapolites in different cuts
Terrazzo with fluorescent wernerite

Despite its often well-developed, clear and shiny crystals, scapolite is one of the seldom used gemstones because it is sensitive to acids and cannot tolerate heat. Depending on the color variety, there is a risk of confusion with chrysoberyl , citrine and golden beryl (yellow), rose quartz (pink) and amethyst (violet) as well as titanite (brownish-yellow, reddish-brown) and various tourmalines (multicolored). Scapolites with chatoyance (cat's eye effect) and asterism (star effect) are also known.

Occasionally, scapolite ( Wernerite ) is also used in terrazzo floors, whereby its fluorescent properties are used to achieve a kind of “chameleon effect” in the appearance of the surface pattern. The scapolites, which are white to almost colorless in daylight, light up under a UV source (e.g. black light ) in a strong yellow to orange.

See also

literature

  • José Bonifácio de Andrada e Silva : Brief description of the properties and characteristics of some new fossils from Sweden and Norway, along with some chemical remarks about them . In: General Journal of Chemistry . tape 4 , 1800, p. 28–39 ( rruff.info [PDF; 2,4 MB ; accessed on March 4, 2017] p. 12 as Scapolit ).
  • Louise Levien, JJ Papike: Scapolite crystal chemistry: aluminum-silicon distributions, carbonate group disorder, and thermal expansion . In: American Mineralogist . tape 61 , 1976, p. 864–877 ( minsocam.org [PDF; 1.3 MB ; accessed on March 4, 2017]).
  • RC Peterson, Gabrielle Donnay, Yvon Lepage: Sulfate Disorder in Scapolite . In: Canadian Mineralogist . tape 17 , 1979, pp. 53–61 ( rruff.geo.arizona.edu [PDF; 71 kB ; accessed on March 4, 2017]).
  • Elena V. Sokolova, Yurii K. Kabalov, Barbara L. Sherriff, David K. Teertstra, David M. Jenkins, Gerald Kunath-Fandrei, Steffen Goetz, Christian Jäger: Marialite: Rietveld structure-refinement and 29 Si MAS and 27 Al satellite transition NMR spectroscopy . In: Canadian Mineralogist . tape 34 , 1996, pp. 1039-1050 ( rruff.info [PDF; 96 kB ; accessed on March 4, 2017]).
  • David K. Teerstra, Barbara L. Sherriff: Scapolite cell-parameter trends along the solid-solution series . In: American Mineralogist . tape 81 , 1996, pp. 169–180 ( minsocam.org [PDF; 1.1 MB ]).
  • Peter Bayliss: Mineral nomenclature: scapolite . In: Mineralogical Magazine . tape 51 , 1997, p. 176 ( rruff.info [PDF; 81 kB ; accessed on March 4, 2017]).
  • JC Bridges, CMO Alexander, R. Hutchison, IA Franchi, CT Pillinger: Na-, Cl-rich mesostases in Chainpur (LL3) and Parnallee (LL3) chondrules . In: Meteoritics . tape 32 , 1997, pp. 555-566 , bibcode : 1997M & PS ... 32..555B .
  • Deane K. Smith, Andrew C. Roberts, Peter Bayliss, Friedrich Liebau: A systematic approach to general and structure-type formulas for minerals and other inorganic phases . In: American Mineralogist . tape 83 , 1998, pp. 126–132 ( minsocam.org [PDF; 89 kB ; accessed on March 4, 2017]).
  • David K. Teerstra, M. Schindler, Barbara L. Sherriff, Frank C. Hawthorne: Silvialite, a new sulfate-dominant member of the scapolite group with an Al-Si composition near the I4 / m-P4 2 / n phase transition . tape 63 , no. 3 , 1999, p. 321–329 ( rruff.geo.arizona.edu [PDF; 636 kB ; accessed on March 4, 2017]).
  • Barbara L. Sherriff, Elena V. Sokolova, Yurii K. Kabalov, David M. Jenkins, Gerald Kunath-Fanderei, Steffen Goetz, Christian Jäger, Julius Schneider: Meionite: Rietveld Structure Refinement, 29 Si MAS and 27 Al SATRAS NMR Spectroscopy, and Comments on the Marialite-Meionite Series . In: Canadian Mineralogist . tape 38 , 2000, pp. 1201–1213 ( rruff.geo.arizona.edu [PDF; 1.7 MB ; accessed on March 4, 2017]).
  • Marialite . 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; 74 kB ; accessed on March 4, 2017]).
  • Meionite . 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; 74 kB ; accessed on March 4, 2017]).
  • Yuanming Pan, Ping Dong: Bromine in Scapolite-group Minerals and Sodalite: XRF Microprobe Analysis, Exchange Experiments, and Application to Skarn Deposits . In: Canadian Mineralogist . tape 41 , 2003, p. 529-540 ( rruff.geo.arizona.edu [PDF; 790 kB ; accessed on March 4, 2017]).

Web links

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

Individual evidence

  1. ↑ a b c d David K. Teerstra, Barbara L. Sherriff: Scapolite cell-parameter trends along the solid-solution series . In: American Mineralogist . tape 81 , 1996, pp. 169–180 ( minsocam.org [PDF; 1.1 MB ]).
  2. ↑ a b c d e f g h i j Marialite . 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; 74  kB ; accessed on March 4, 2017]).
  3. ↑ a b c d e f g h i j Meionite . 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; 74  kB ; accessed on March 4, 2017]).
  4. ↑ a b DK Smith, AC Roberts, P. Bayliss, F. Liebau: A systematic approach to general and structure-type formulas for minerals and other inorganic phases . In: American Mineralogist . tape 83 , 1998, pp. 126–132 ( minsocam.org [PDF; 89 kB ; accessed on March 4, 2017]).
  5. ↑ a b Yuanming Pan, Ping Dong: Bromine in Scapolite-group Minerals and Sodalite: XRF Microprobe Analysis, Exchange Experiments, and Application to Skarn Deposits . In: Canadian Mineralogist . tape 41 , 2003, p. 529-540 ( rruff.geo.arizona.edu [PDF; 790 kB ; accessed on March 4, 2017]).
  6. ↑ a b David K. Teerstra, M. Schindler, Barbara L. Sherriff, Frank C. Hawthorne: Silvialite, a new sulfate-dominant member of the scapolite group with an Al-Si composition near the I4 / m-P4 2 / n phase transition . tape 63 , no. 3 , 1999, p. 321–329 ( rruff.geo.arizona.edu [PDF; 636 kB ; accessed on March 4, 2017]).
  7. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  8. ↑ José Bonifácio de Andrada e Silva : Brief statement of the properties and characteristics of some new fossils from Sweden and Norway, along with some chemical remarks about them . In: General Journal of Chemistry . tape  4 , 1800, p. 28–39 ( rruff.info [PDF; 2,4 MB ; accessed on March 4, 2017] p. 12 as Scapolit ).
  9. ^ Peter Bayliss: Mineral nomenclature: scapolite . In: Mineralogical Magazine . tape 51 , 1997, p. 176 ( rruff.info [PDF; 81 kB ; accessed on March 4, 2017]).
  10. ↑ Elena V. Sokolova, Yurii K. Kabalov, Barbara L. Sherriff, David K. Teertstra, David M. Jenkins, Gerald Kunath-Fandrei, Steffen Goetz, Christian Jäger: Marialite: Rietveld structure-refinement and 29 Si MAS and 27 Al satellite transition NMR spectroscopy . In: Canadian Mineralogist . tape 34 , 1996, pp. 1039-1050 ( rruff.info [PDF; 96 kB ; accessed on March 4, 2017]).
  11. ↑ Barbara L. Sherriff, Elena V. Sokolova, Yurii K. Kabalov, David M. Jenkins, Gerald Kunath-Fanderei, Steffen Goetz, Christian Jäger, Julius Schneider: Meionite: Rietveld Structure Refinement, 29 Si MAS and 27 Al SATRAS NMR Spectroscopy , and Comments on the Marialite-Meionite Series . In: Canadian Mineralogist . tape 38 , 2000, pp. 1201–1213 ( rruff.geo.arizona.edu [PDF; 1.7 MB ; accessed on March 4, 2017]).
  12. ↑ Carl Friedrich Alexander Hartmann: Textbook of Mineralogy and Geology: for use in higher educational establishments and for self-teaching for every educated person. 1st part: Mineralogy . C. Gerold'sche Buchhandlung, Nuremberg 1835, p. 171 ( limited preview in Google Book search).
  13. ↑ Mindat - Gabbronite
  14. ↑ JC Bridges, CMO Alexander, R. Hutchison, IA Franchi, CT Pillinger: Na-, Cl-rich mesostases in Chainpur (LL3) and Parnallee (LL3) chondrules . In: Meteoritics . tape 32 , 1997, pp. 555-566 , bibcode : 1997M & PS ... 32..555B .
  15. ^ Mineral Atlas: Marialith
  16. ↑ Mineral Atlas: Mejonit
  17. ^ Precious stone etiquette from Prof. Leopold Rössler - Scapolite
  18. ↑ realgems.org - Scapolite (with image examples of cut scapolites)