Spessartine

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Spessartine
Spessartine-132070.jpg
Spessartine crystals and twins on orthoclase from the "Wushan Spessartine Mine", Yunxiao , Zhangzhou, Fujian, China
( total size of the stage : 5.8 × 5.1 × 2.2 cm)
General and classification
other names

Manganese clay garnet

chemical formula Mn 3 Al 2 [SiO 4 ] 3
Mineral class
(and possibly department) 		Silicates and germanates - island silicates (nesosilicates)
System no. to Strunz
and to Dana 		9.AD.25 ( 8th edition : VIII / A.08)
51.04.03a.03
Similar minerals other garnets, andalusite, chrysoberyl, fire opal, hessonite, titanite, topaz
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Ia 3 d (No. 230)Template: room group / 230
Lattice parameters a  = 11,621  Å
Formula units Z  = 8
Frequent crystal faces Icositetrahedron, rhombic dodecahedron
Physical Properties
Mohs hardness 7 to 7.5
Density (g / cm 3 ) measured: 4.190; calculated: 4.1902
Cleavage no
Break ; Tenacity uneven to scalloped
colour orange, yellow, brownish red to dark red, black
Line color White
transparency transparent to translucent
shine Glass gloss to fat gloss
Crystal optics
Refractive index n  = natural: 1.790 to 1.820, synthetic: 1.800
Birefringence δ = rarely abnormally birefringent

Spessartine , also known as manganese alumina garnet , is a frequently occurring mineral from the garnet group within the mineral class of " silicates and germanates ". It crystallizes in the cubic crystal system with the idealized composition Mn 3 Al 2 [SiO 4 ] 3 , so from a chemical point of view it is a manganese - aluminum silicate, which structurally belongs to the island silicates .

Spessartine is the manganese analogue of almandine (Fe 3 Al 2 [SiO 4 ] 3 ) and pyrope (Mg 3 Al 2 [SiO 4 ] 3 ) and forms a mixed crystal series with these , the so-called "pyralspite series". Since Spessartine also works with the other garnet minerals andradite (Ca 3 Fe 2 3+ [SiO 4 ] 3 ), calderite (Mn 3 Fe 2 3+ [SiO 4 ] 3 ) and grossular (Ca 3 Al 2 [SiO 4 ] 3 ) Forms mixed crystals, Spessartine shows a correspondingly wide spectrum of composition with more or less large proportions of iron , magnesium and calcium depending on the formation conditions .

The mineral is transparent to translucent and typically develops rhombic dodecahedra or, more commonly, icositetrahedra, as well as combinations of these crystal forms, which appear almost spherical and can reach a diameter of 10 centimeters. It also occurs in coarse or massive aggregates. The color of Spessartine usually varies between orange and yellow, but can also be brown-red through dark red to black.

Etymology and history

Spessartin was named in 1832 by François Sulpice Beudant after the Spessart , because in this low mountain range with the Stengerts near Aschaffenburg one of the historically most important sites for Spessartin was.

The Sommer'sche Steinbruch on Wendelberg near Haibach in the Lower Franconian district of Aschaffenburg is considered to be the type locality . The quarry, which has not been used since 1985 but has been abandoned, and the surrounding area is protected as a natural monument for botanical reasons. Accordingly, collecting is only permitted there with special permission for excursion, research and teaching purposes.

Georg Menzer clarified the crystal structure in 1929.

classification

The structural classification of the International Mineralogical Association (IMA) is one of the Spessartin to Garnet supergroup, where he along with almandine , Andradite , Calderit , Eringait , Goldmanit , Grossular , Knorringit , Morimotoit , majorite , Menzerit- (Y) , Momoiit , Rubinit , Pyrope and uvarovite form the garnet group with 12 positive charges on the tetrahedral coordinated lattice position.

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Spessartin belonged to the department of the "island silicates (nesosilicates)" where he collaborated with almandine, Andradite, Calderit, Goldmanit, Grossular, Henritermierit , Hibschite , Holtstamit , Hydrougrandit , Katoit , Kimzeyit , Knorringit, Majorit, Morimotoit, Pyrope , Schorlomit , Uwarowit, Wadalit and Yamatoit (discredited because identical to Momoiit) the "Garnet Group" with the system no. VIII / A.08 .

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 classifies the Spessartine in the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without further anions; Cations in octahedral [6] and usually greater coordination "can be found, where together with almandine, andradite, calderite, goldmanite, grossular, henritermierite, holtstamite, katoite, kimzeyite, knorringite, majorite, morimotoite, pyrope, schorlomite and uwarowite the" Garnet group "with the system no. 9.AD.25 forms. The garnet compounds blythite, hibschite, hydroandradite and skiagite, which are no longer regarded as minerals, were also included in this group. Wadalite , at that time still grouped with the grenades, proved to be structurally different and is now assigned to a separate group with chloromayenite and fluoromayenite . The garnets irinarassite , hutcheonite , kerimasite , toturite , menzerite (Y) and eringaite described after 2001 would have been classified in the garnet group.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , also classifies the Spessartine in the “island silicate minerals ” department. Here it is together with pyrope, almandine, knorringite, majorite and calderite in the "garnet group (pyralspite series)" with the system no. 51.04.03a to be found in the subsection “ Island silicates: SiO 4 groups only with cations in [6] and> [6] coordination ”.

composition

Spessartin with the idealized composition [X] Mn 2+ 3 [Y] Al 3+ [Z] Si 3 O 12 is the manganese -Analog of Pyrop ( [X] Mg 2+ 3 [Y] Al [Z] Si 3 O 12 ) and occurs in nature mostly as a mixed crystal, predominantly with almandine. There is also unlimited miscibility with the other aluminum grenades, at least at geologically relevant temperatures, according to the exchange reactions

  • [X] Mn 2+ = [X] Mg 2+ (pyrope)
  • [X] Mn 2+ = [X] Fe 2+ (almandine)
  • [X] Mn 2+ = [X] Ca 2+ (grossular)

At the octahedral Y position, Al 3+ can be replaced by Fe 3+ , according to the exchange reaction

  • [Y] Al 3+ = [Y] Fe 3+ (andradite / calderite)

In high pressure rocks of the western Alps, calderite-rich and Spessartine-rich garnets occur side by side, which indicates a miscibility gap of 40–65 mol% calderite.

Spessartine can contain significant amounts of fluorine (F - ) and hydrogen (as OH - ). The charge equalization takes place through vacancies on the silicon position in accordance with the exchange reactions

  • [Z] Si 4+ + O 2- 4 = [Z] □ + F - 4
  • [Z] Si 4+ + O 2- 4 = [Z] □ + (OH) - 4

During the metamorphosis of pelites , almandins that are rich in Spessartine and grossular form form the core of the zoned garnet. With increasing metamorphosis, i. H. As the temperature and pressure rise, the garnets become richer in almandine and pyrope. Rims rich in Spessartine, however, indicate garnet growth with descending metamorphosis and low temperatures. The correlation of the iron, manganese and magnesium contents allows conclusions to be drawn about the mineral reaction through which garnet was formed during metamorphosis.

Crystal structure

Spessartine crystallizes with cubic symmetry in space group Ia 3 d (space group no.230) and 8 formula units per unit cell . There are numerous provisions for the edge length of the cubic unit cell of both natural mixed crystals and synthetic spessartines. For the pure Spessartine terminal, the lattice parameter z. B. given with a  = 11.621 Å or a  = 11.6155 Å. Template: room group / 230

The structure is that of garnet . Manganese (Mn 2+ ) occupies the dodecahedral of 8 oxygen ions surrounded X positions, aluminum (Al 3+ ) the octahedrally by 6 oxygen ions surrounded Y-position and the tetrahedrally by 4 oxygen ions surrounded Z position is exclusively with silicon (Si 4+ ) occupied.

As with many natural aluminum grenades , birefringence has been observed in fluorine-containing spessartine from the Henderson molybdenite deposit in Clear Creek County , Colorado . The cause of this optical anisotropy has not yet been finally clarified. No reliable indications of a lowering of symmetry and order of cations could be found. Lattice stresses (stress birefringence) remain the cause of the birefringence, even if a partially orderly distribution of cations or anions (O, OH, F) cannot finally be ruled out. On the other hand, with still (OH, F) -rich spessartine from the Wushan Spessartine mine in Yunxiao , Fujian Province , China, tetragonal symmetry with an ordered distribution of vacancies on the tetrahedral positions was observed.

Varieties and modifications

Perfect Spessartine ikositetrahedron from Nani, Loliondo, Arusha , Tanzania
  • As mandarin garnet or Kunene Spessartin a bright orange is variety of Spessartin from Marie River , a tributary of the Kunene in Namibia called.
  • Umbalith is an orange-colored Spessartine mixed crystal named after the Umba valley in Tanzania with proportions of almandine, grossular and pyrope. Occasional, additional foreign admixtures of vanadium and chromium can cause a color change from blue-green to purple, known as the alexandrite effect .
  • Spandite is a historical, no longer in use name for a Spessartine-Andradite mixed crystal. The name was proposed by Lewis Leigh Fermor (1880-1954) in 1909 , but did not catch on.

Spessartite (after H. Rosenbusch , 1896), on the other hand, is not a synonym for Spessartine, as is sometimes wrongly read, but an igneous rock of the Kersantite-Spessartite series of dark gray to black color belonging to the lamprophyres .

Education and Locations

Spessartine forms as a secondary part in granites rich in manganese and granite pegmatites . However, it can also arise through regional metamorphosis in manganese-rich sediments such as the " Wetzschiefern " of the Ardennes . The accompanying minerals include albite and other alkali feldspars , alleghanyite , apatite , beryl , bixbyite , galaxite , muscovite , pseudobrookite , pyrox mangite , quartz , rhodonite , tephroite , topaz and tourmaline .

As a frequent mineral formation, Spessartin can be found at many localities, whereby so far (as of 2012) around 1000 localities are known. In addition to its type locality Wendelberg, the mineral occurred in Germany in many other places in the Bavarian Forest (Arnbruck, Zwiesel), in the Klemmbach quarry near Schweighof / Badenweiler in Baden-Württemberg, near Bad Harzburg in Lower Saxony, in several places in the Eifel in Rhineland -Pfalz and in the Harz between Saxony-Anhalt and Thuringia as well as in Schneeberg , Königshain and Döbschütz in Saxony.

In Austria, Spessartin has so far been found mainly in Carinthia and Styria ( Friesach - Hüttenberg , Koralpe ), but also in the Lower Austrian Waldviertel , the Hohe Tauern in Salzburg and in East Tyrol .

In Switzerland, the mineral has so far only been found in a few places in the cantons of Graubünden and Valais .

Other locations include Afghanistan, Egypt, Antarctica, Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Finland, France, Ghana, Greece, India, Italy, Japan, Canada, Kazakhstan, Kyrgyzstan, Korea , Madagascar, Morocco, Mozambique, Myanmar, Namibia, New Zealand, Nigeria, Norway, Pakistan, Peru, Poland, Portugal, Romania, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Spain, Sri Lanka, South Africa, Taiwan, Tanzania, Thailand, the Czech Republic, Turkey, Ukraine, Hungary, the United Kingdom (Great Britain) and the United States of America (USA).

Spessartine could also be detected in rock samples from the moon .

  • Spessartine (orange) with fluorite (light blue) and quartz (colorless) on orthoclase from China

  • Spessartine (orange-red) and lepidolite from Italy

  • Spessartine (dark red), aquamarine and Schörl (black tourmaline ) on albite from Pakistan

  • Dark red Spessartine as an inclusion in almost colorless beryl from Pakistan

  • Wine-red Spessartine of unusual shape and size (7.5 × 6.5 × 3 cm) from Minas Gerais, Brazil

use

Like most other types of garnet that are worth cutting, Spessartine is mainly used as a gemstone . Depending on the color, it can be confused with andalusite , chrysoberyl , fire opal , hessonite , titanite or topaz .

Due to the variety of colors, caused by the extensive mixed crystal formation of the garnet, the gemstone trade has meanwhile switched to assigning the garnets to the individual types of garnet, not according to their chemical composition, which is often difficult to determine, but according to their respective color nuances, which accordingly only serve as color names. The yellow to orange garnets are referred to as Spessartine or, alternatively, also as grossular.

literature

Web links

Commons : Spessartin  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e f g 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.  541 .
  2. ^ A b GA Novak and GV Gibbs: The crystal chemistry of the silicate garnets . In: The American Mineralogist . tape 56 , 1971, p. 791–825 ( rruff.info [PDF; 2,3 MB ; accessed on May 4, 2018]).
  3. ↑ a b c d BJ Skinner: Physical properties of end members of the garnet group . In: The American Mineralogist . tape 41 , 1956, pp. 428–436 ( minsocam.org [PDF; 522 kB ; accessed on May 5, 2018]).
  4. ↑ a b c d DK Teertstra: Index-of-refraction and unit-cell constraints on cation valence and pattern of order in garnet-group minerals . In: The Canadian Mineralogist . tape 44 , 2006, pp. 341–346 ( rruff.info [PDF; 197 kB ; accessed on May 5, 2018]).
  5. ^ Spessartine , 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 72.4 kB).
  6. ^ A b Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags-GmbH., Munich et al. 2002, ISBN 3-405-16332-3 , p. 120 .
  7. ↑ a b c d JR Smyth, RE Madel, TC McCormick, JL Munoz, and GR Rossman: Crystal structure refinement of a F-bearing spessartine garnet . In: The American Mineralogist . tape 75 , 1990, pp. 314-318 ( minsocam.org [PDF; 643 kB ; accessed on May 27, 2018]).
  8. ↑ a b c Anne M. Hofmeister, Rand B. Schaal, Karla R. Campbell, Sandra L. Berry and Timothy J. Fagan: Prevalence and origin of birefringence in 48 garnets from the pyrope-almandine-grossularite-spessartine quaternary . In: The American Mineralogist . tape 83 , 1998, pp. 1293–1301 ( minsocam.org [PDF; 105 kB ; accessed on May 27, 2018]).
  9. ^ FS Beudant: Traité Élémentaire de Minéralogie . 2nd Edition. VERDIÈRE, Paris 1832 ( rruff.info [PDF; 97 kB ; accessed on May 27, 2018]).
  10. ^ Mindat - type locality summer quarry, Wendelberg, Haibach, Aschaffenburg, Spessart, Franconia, Bavaria, Germany
  11. ^ Bavarian State Office for the Environment - Geotope cadastre : quarry at Wendelberg W von Haibach. Geotope no. 671A032, ID 6021GT000011 (PDF 194.3 kB).
  12. ↑ G. Menzer: The crystal structure of the grenade . In: Journal of Crystallography - Crystalline Materials . tape 69 , 1929, pp. 300-396 , doi : 10.1524 / zkri.1929.69.1.300 .
  13. ^ A b c Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( rruff.info [PDF; 1.1 MB ; accessed on April 28, 2020]).
  14. ↑ a b c Jibamitra Ganguly, Weiji Cheng, Massimiliano Tirone: Thermodynamics of alimosilicate garnet solid solution: new experimental data, an optimized model, and thermodynamic applications . In: Contributions to Mineralogy and Petrology . tape 126 , 1996, pp. 137–151 ( researchgate.net [PDF; 1.8 MB ; accessed on May 22, 2018]).
  15. ↑ a b Hidehiko Shimazaki: Grosslar-Spessartine-Almandine Garnets from some Japanese Scheelite Skarns . In: The Canadian Mineralogist . tape 15 , 1977, pp. 74–80 ( rruff.info [PDF; 602 kB ; accessed on May 21, 2018]).
  16. ↑ Charles Geiger and Anne Feenstra: Molar volumes of mixing of almandine-pyrope and almandine-spessartine garnets and the crystal chemistry and thermodynamic-mixing properties of the aluminosilicate garnets . In: The American Mineralogist . tape 82 , 1997, pp. 571-581 ( minsocam.org [PDF; 213 kB ; accessed on May 21, 2018]).
  17. ↑ U. Rodehorst, MA Carpenter, T. Boffa Ballaran, CA Geiger: Local structural heterogeneity, mixing behavior and saturation effects in the grossular-spessartine solid solution . In: Physics and Chemistry of Minerals . tape 31 , 2004, p. 387-404 ( researchgate.net [PDF; 578 kB ; accessed on May 27, 2018]).
  18. ^ Pete J. Dunn: On the Validity of Calderite . In: Canadian Mineralogist . tape 17 , 1979, pp. 569–571 ( rruff.info [PDF; 199 kB ; accessed on April 28, 2018]).
  19. ↑ a b B. Cenki-Tok & C. Chopin: CALDERITE – SPESSARTINE GARNETS IN ECLOGITIC METACHERTS . In: Communications from the Austrian Mineralogical Society . tape 150 , 2005, pp. 623-632 ( psu.edu [PDF; 97 kB ; accessed on May 27, 2018]).
  20. ↑ Victor G. Korinevsky: SPESSARTINE-Andradite IN Scapolite pegmatite, ILMENY MOUNTAINS, RUSSIA . In: The Canadian Mineralogist . tape 53 , 2015, p. 623-632 ( researchgate.net [PDF; 1,2 MB ; accessed on May 27, 2018]).
  21. ↑ a b Massimo Boiocchi, Fabio Bellatreccia, Giancarlo Della Ventura and Roberta Oberti: On the symmetry and atomic ordering in (OH, F) -rich spessartine: towards a new hydrogarnet end-member . In: Journal of Crystallography . tape 227 , 2012, p. 385-395 ( researchgate.net [PDF; 279 kB ; accessed on April 28, 2018]).
  22. ↑ RJ Tracy: Compositional zoning and inclusions in metamorphic minerals . In: Reviews in mineralogy . tape 10 , 1982, pp. 355-397 .
  23. ↑ Uta Rodehorst, Charles A. Geiger and Thomas Armbruster: The crystal structures of grossular and spessartine between 100 and 600 K and the crystal chemistry of grossular-spessartine solid solutions . In: The American Mineralogist . tape 87 , 2002, pp. 542–549 ( rruff.info [PDF; 208 kB ; accessed on May 24, 2018]).
  24. ↑ a b c Maximilian Glas and others: Garnet . In: Christian Weise (ed.): ExtraLapis . tape 9 . Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 16 .
  25. ^ Hans Murawski, Wilhelm Meyer: Geological dictionary . 12th edition. Spektrum Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-1810-4 , pp. 156 .
  26. ^ Mindat - Spessartine
  27. ↑ Mindat - localities for Spessartine
  28. ↑ Mindat - moon, short description of the location and mineral list
  29. ↑ Bernhard brother embellished stones . Neue Erde Verlag, 2005, ISBN 3-89060-025-5 , p. 68-69 .