Almandine


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Almandine
Almandine.jpg
Almandine on gray-green slate from Granatenkogel , Ötztal Alps, Tyrol (size: 19 cm × 11 cm × 7 cm)
General and classification
other names
  • Iron clay garnet
  • Iron-alumina garnet
chemical formula Fe 3 Al 2 [SiO 4 ] 3
Mineral class
(and possibly department)
Island silicates (nesosilicates)
System no. to Strunz
and to Dana
9.AD.25 ( 8th edition : VIII / A.08)
51.04.03a.02
Similar minerals Pyrope (Mg 3 Al 2 [SiO 4 ] 3 )
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  = 11.526  Å
Formula units Z  = 8
Frequent crystal faces Icositetrahedron, rhombic dodecahedron
Physical Properties
Mohs hardness 7 to 7.5
Density (g / cm 3 ) measured: 4.318; calculated: 4.3184
Cleavage none, segregation after {110} possible
Break ; Tenacity slightly mussel-like; brittle
colour red to red-violet, black-brown
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive index n  = 1,830 (depending on the chemical composition)
Birefringence none, mixed crystals sometimes abnormally birefringent
Other properties
Chemical behavior vulnerable to mineral acids

Almandine , also known as iron clay garnet or iron clay garnet , is a mineral from the group of garnets within the mineral class of " silicates and germanates ". It crystallizes in the cubic crystal system with the idealized composition Fe 3 Al 2 [SiO 4 ] 3 , so from a chemical point of view it is an iron - aluminum silicate, which structurally belongs to the island silicates .

Almandine is the iron analogue of spessartine (Mn 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 almandine also forms mixed crystals with grossular (Ca 3 Al 2 [SiO 4 ] 3 ), natural almandine has a correspondingly broad spectrum of composition with more or less large proportions of manganese , magnesium and calcium depending on the formation conditions . In addition, traces of sodium , potassium , chromium and vanadium , more rarely also scandium , yttrium , europium , ytterbium , hafnium , thorium and uranium may be present.

The mineral is transparent to translucent and typically develops rhombic dodecahedra or icositetrahedron, as well as combinations of these crystal forms, which appear almost spherical. Granular to massive mineral aggregates are also often found . In general, almandine crystals can reach a size of several centimeters in diameter. However, giant crystals with a diameter of up to one meter were also known. The color of almandine usually varies between dark red and red-violet, but can also be brownish-red to almost black.

Almandine is the most common type of garnet around the world and is often found in grades that are worth grinding and with a strong, glass-like sheen , which makes it a coveted gemstone .

Etymology and history

Almandine was already known to Pliny the Elder (approx. 23–79 AD) under the name alabandicus and generally belonged to the “ carbunculus ”, i.e. red gemstones. It was named after the ancient city of Alabanda in Caria (Asia Minor, today in the Turkish province of Aydın ), where the stone is said to have been worked. Alabanda is therefore also considered a type locality for almandine.

In the Middle Ages, various variations of the name were in use such as alabandina , alabandra and alabanda . Albertus Magnus (around 1200-1280) introduced the name alamandina , which almost corresponded to the current form.

Around 1800 the designation almandine was finally fixed on the iron clay garnet by Dietrich Ludwig Gustav Karsten (1768–1810).

Curiously, the manganese sulfide alabandin , which was first described in 1784 and has a similar name, was also named after the Turkish town of Alabanda, although it has not yet been detected there.

classification

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

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of almandine belonged to the department of the "island silicates (nesosilicates)" where he collaborated with Andradite, Calderit, Goldmanit, Grossular, Henritermierit , Hibschite , Holtstamit , Hydrougrandit , katoite , Kimzeyite , knorringite , majorite , morimotoite , pyrope , schorlomite , Spessartine, uwarowite , wadalite and yamatoite (discredited because it is identical to momoiite) the "garnet group" with 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 almandine 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 larger coordination “can be found, where it is found together with andradite, calderite, goldmanite, grossular, henritermierite, holtstamite, katoite, kimzeyite, knorringite, majorite, momoiite, morimotoite, pyrope, schorlomite, spessartine 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 almandine in the category of "island silicate minerals ". Here it is together with pyrope, spessartine, 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 ”.

Chemism

Almandin with the idealized composition [X] Fe 2+ 3 [Y] Al 3+ [Z] Si 3 O 12 is the iron -Analog of Pyrop ( [X] Mg 2+ 3 [Y] Al [Z] Si 3 O 12 ) and occurs in nature mostly as a mixed crystal with pyrope, spessartine and grossular. With these end links there is unlimited miscibility, at least at geologically relevant temperatures, according to the exchange reactions

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

So far, no indications of a miscibility gap have been found for the mixture series Almandin-Grossular. Only for pyrope-rich pyrope-grossular-almandine mixed crystals was a miscibility gap detected at temperatures below approximately 600 ° C.

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

  • [Y] Al 3+ = [Y] Fe 3+ (Skiagit)

Garnets rich in almandine are usually formed during the metamorphosis of pelites and are often zoned. With increasing metamorphosis, i. H. With increasing temperature and pressure, garnets with a Spessartine and grossular-rich core grow, which become richer in almandine and pyrope towards the edge. 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

Almandine crystallizes with cubic symmetry in the 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 almandins. For the pure almandine terminal the lattice parameter z. B.  indicated with a  = 11.526 Å or a = 11.525 Å. Template: room group / 230

The structure is that of garnet . Iron (Fe 2+ ) occupies the X positions dodecahedrally surrounded by 8 oxygen ions and carries out a clearly asymmetrical oscillation around the center of the position. The iron ion is a bit too small for the dodecahedron and "slagks" a bit. Aluminum (Al 3+ ) occupies the Y position, which is surrounded by 6 oxygen ions in an octahedral manner, and the Z position, which is surrounded by 4 oxygen ions in an octahedral manner, is exclusively occupied by silicon (Si 4+ ).

Birefringence and the formation of sector zoning have been observed in some natural almandine grossular mixed crystals. The explanation for this birefringence is a partially ordered distribution of Fe and Mg on the one hand and Ca on the other hand on the X-position of the garnet structure. This goes hand in hand with a lowering of symmetry to the tetragonal space group I4acd. More recent studies on a large group of aluminum grenades do not find any reliable evidence of a lowering of symmetry and ordering of cations. Lattice stresses ( stress birefringence ) are named as the cause of the birefringence .

Varieties and modifications

Pink rhodolite from Mexico

Rhodolites , also commonly known as oriental garnets , are pink to red-violet almandine varieties , which, strictly speaking, are almandine-pyrope mixed crystals with a mixture ratio of magnesium: iron ≈ 2: 1 and a density of ≈ 3.84 g / cm³. Well-known occurrences of rhodolite include Brazil , India , Kenya , Madagascar , Mexico , Zambia and Tanzania .

The Malaya garnet is also an almandine-pyrope mixed crystal with the same find areas as rhodolite , but of a more reddish-orange color. It was named after the Swahili word malaya for "outside the family".

Education and Locations

Almost black almandine from the " Russell Garnet Mine", Hampden County , Massachusetts, USA (comparative scale: 1 "(= 2.54 cm) with a notch at 1 cm)

Almandine is a characteristic mineral of metamorphic rocks such as mica schist , amphibolite , granulite and gneiss . From around 450 ° C, garnet rich in almandine forms in the reaction of chloritoid + biotite + H 2 O to garnet + chlorite . From approx. 600 ° C, garnets form when staurolite is broken down , and garnets can still be formed again even when the rock begins to melt, e.g. B. in the reaction of biotite + sillimanite + plagioclase + quartz to garnet + potassium feldspar + melt. Garnet only degrades into spinel + quartz at temperatures above 900 ° C or into orthopyroxene + sillimanite at high pressures .

Garnets rich in almandine can also form in igneous rocks such as granite and granite- pegmatite . The crystals are usually embedded in the mother rock (blasts) and separated from other almandine crystals. Garnets with the highest known almandin content of 86.7% (as of 1995) were found at Kayove in Rwanda , but almandine-rich crystals of around 76% have also occurred in Germany, including ground maize .

As a frequent mineral formation, almandine can be found at many sites, with around 2200 sites being known to date (as of 2014). Accompanied will almandine among other things, various amphibole , chlorite , plagioclase and pyroxene and of andalusite , biotite , cordierite , hematite , kyanite , sillimanite and staurolite .

In addition to its type locality Alabanda, the mineral has so far only appeared in Turkey in the garnet amphibolites near Çamlıca on the Asian side of Istanbul.

In Germany, almandine could be found in several places in the Black Forest ( Freiburg im Breisgau , Grube Clara in Oberwolfach) in Baden-Württemberg, in many places in Bavaria ( Bavarian Forest , Upper Palatinate Forest , Spessart ), near Ruhlsdorf / Eberswalde-Finow in Brandenburg, in some Places in the Odenwald (Erlenbach, Lindenfels), near Bad Harzburg in Lower Saxony, near Bad Doberan in Mecklenburg-Western Pomerania, near Perlenhardt and at Drachenfels ( Königswinter ) in North Rhine-Westphalia, in many places in the Eifel in Rhineland-Palatinate, in the pit "God's reward" can be found near Schmelz in Saarland, in the Diethensdorf quarry and near Penig, as well as in many places in the Ore Mountains in Saxony and in some places in Schleswig-Holstein ( Barmstedt , Kiel , Schleswig , Travemünde ).

In Austria, the mineral has so far been found mainly in Carinthia in the Gurktal Alps and the Saualpe , in the Koralpe from Carinthia to Styria and in the Niedere Tauern , but also in several places in Lower Austria ( Wachau , Waldviertel ), Salzburg ( Hohe Tauern ), in the Tyrolean Gurgler Valley and Zillertal as well as at some sites in Upper Austria and Vorarlberg.

In Switzerland, almandin finds have so far only been known from a few places in the cantons of Ticino ( Gotthard massif ) and Valais ( Binntal ).

The Ishikawa pegmatites in the prefecture of Fukushima on the Japanese island of Honshū and Shengus on the Haramosh in Pakistan, where well-formed almandine crystals of up to 15 centimeters in diameter have been discovered, are known for their extraordinary almandin finds . Crystals up to 5 centimeters in size were found in the mica schists and gneisses near Fort Wrangell in Alaska and near Bodø in Norway. In Italy, in South Tyrol , almandins of considerable size were found on the Granatenkogel in the Seebertal .

Other locations include Afghanistan, Egypt, Ethiopia, Algeria, Angola, Antarctica, Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Burkina Faso, Chile, China, the Democratic Republic of the Congo, Finland, France and French Guiana , Greece, Greenland, Guatemala, India, Ireland, Israel, Canada, Columbia, Korea, Madagascar, Malawi, Mexico, Mongolia, Myanmar, Namibia, Nepal, New Caledonia, New Zealand, Norway, Poland, Portugal, Romania, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Slovenia, Spain, Sri Lanka, South Africa, Taiwan, Tajikistan, Thailand, the Czech Republic, Ukraine, Hungary, Uzbekistan, the United Kingdom (UK) and the United States of America (USA).

Almandine was also found in rock samples from the moon .

use

Oval cut almandine from Jaipur (Rajasthan), India (size: 3ct64)

Like most of the other minerals in the garnet family, almandine is primarily used as a gemstone , which is cut into a facet shape or into cabochons , depending on its purity and clarity . Less noble varieties, i.e. varieties that are too dark and opaque, are also used as abrasives .

There is a particular risk of confusion with the various types of garnet due to the predominant mixed crystal formation between the individual end links. In addition, almandine can also be confused with ruby , spinel and red tourmalines . Due to the difficult differentiation, the different garnet names are now often used in the gemstone trade as a color designation, with almandine and rhodolite representing the pink to purple garnets.

The largest known and cut almandine gemstone to date is a 175  ct cabochon held at the Smithsonian Institution in Washington, DC.

See also

literature

Web links

Commons : Almandine  - collection of images, videos and audio files
Wiktionary: Almandine  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. 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.  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 April 27, 2020]).
  3. ^ A b c d Brian J. 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 April 27, 2020]).
  4. a b c d David K. 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 April 27, 2020]).
  5. a b Almandine , in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 69.2 kB )
  6. a b Dana T. handles, Dorian M. Hatch, Williem Revell Phillips, Seyfi Kulakdiz: Crystal chemistry and symmetry of a birefringent tetragonal pyralspite75-grandite25 garnet . In: The American Mineralogist . tape 77 , 1992, pp. 399-406 ( rruff.info [PDF; 1.1 MB ; accessed on April 27, 2020]).
  7. ^ A b c Denis Brown, Roger A. Mason: An Occurrence of Sectored Birefrigence in Almandine from the Gagnon Terrane, Labrador . In: The Canadian Mineralogist . tape 32 , 1994, pp. 105–110 ( rruff.info [PDF; 855 kB ; accessed on April 27, 2020]).
  8. a b Maximilian Glas et al .: Granat . In: Christian Weise (ed.): ExtraLapis . tape 9 . Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 24 .
  9. Maximilian Glas et al .: Granat . In: Christian Weise (ed.): ExtraLapis . tape 9 . Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 3 .
  10. a b c Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 168 .
  11. a b Mindat - type locality Alabanda, Aydin Province, Aegean Region, Turkey
  12. Ludwig August Emmerling: Textbook of Mineralogy, Volume 1, Edition 2 , Giessen 1802 in the Google book search
  13. ^ Mindat - Alabandite
  14. ^ A b 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: The American Mineralogist . tape 98 , 2013, p. 785-811 ( main.jp [PDF; 2.0 MB ; accessed on April 27, 2020]).
  15. a b Thomas Armbruster, Charles A. Geiger, George A. Stock: Single-crystal X-ray structure study of synthetic pyrope almandine garnets at 100 and 293K . In: The American Mineralogist . tape 77 , 1992, pp. 512-521 ( rruff.info [PDF; 1,2 MB ; accessed on April 27, 2020]).
  16. ^ A b 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; 214 kB ; accessed on April 27, 2020]).
  17. 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]).
  18. Yu Hariya, Seigo Nakano: Experimental Study of the Solid Solution between the Grossular-Almandine Series . In: Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy = 北海道 大學 理學 部 紀要 . tape 15 , 1972, p. 173-178 ( eprints.lib.hokudai.ac.jp [PDF; 307 kB ; accessed on April 27, 2020]).
  19. 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; 1.9 MB ; accessed on April 27, 2020]).
  20. LIPING WANG, ERIC J. ESSENE AND YOUXUE ZHANG: Direct observation of immiscibility in pyrope-almandine-grossular garnet . In: The American Mineralogist . tape 85 , 2000, pp. 41–46 ( researchgate.net [PDF; 390 kB ; accessed on April 27, 2020]).
  21. Alan B. Woodland, Charles R. Ross: A crystallographic and Mössbauer spectroscopy study of Fe 3 2+ Al 2 Si 3 O 12 -Fe 3 2+ Fe 2 3+ Si 3 O 12 , (almandine- “skiagite”) and Ca 3 Fe 2 3+ Si 3 O 12 -Fe 3 2+ Fe 2 3+ Si 3 O 12 (andradite- “skiagite”) garnet solid solutions . In: Physics and Chemistry of Minerals . tape 21 , 1994, p. 117-132 , doi : 10.1007 / BF00203142 .
  22. Mikhail. N. Taran, M. Dyar Darby, Stanislav. S. Matsyuk: Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2 + + Fe3 + - ›Fe3 + + Fe2 + charge-transfer transition . In: The American Mineralogist . tape 92 , 2007, p. 753-760 ( rruff.info [PDF; 456 kB ; accessed on April 27, 2020]).
  23. RJ Tracy: Compositional zoning and inclusions in metamorphic minerals . In: Reviews in mineralogy . tape 10 , 1982, pp. 355-397 .
  24. CA Geiger, Th. Armbruster, GA Lager, K. Jiang, W. Lottermoser and G. Amthauer: A Combined Temperature Dependent 57 ^ Fe Mössbauer and Single Crystal X-ray Diffraction Study of Synthetic Almandine: Evidence for the Gol'danskii- Karyagin Effect . In: Physics and Chemistry of Minerals . tape 19 , 1992, pp. 121–126 ( researchgate.net [PDF; 696 kB ; accessed on April 27, 2020]).
  25. ^ S. Quartieri, G. Antonioli, G. Artioli, CA Geiger, PP Lottici: A temperature dependent X-ray Absorption Fine Structure study of dynamic X-site disorder in almandine: a comparison to diffraction data . In: Physics and Chemistry of Minerals . tape 24 , 1997, pp. 200–205 ( researchgate.net [PDF; 402 kB ; accessed on April 27, 2020]).
  26. ^ A b 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; 106 kB ; accessed on April 27, 2020]).
  27. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  668 (first edition: 1891).
  28. Maximilian Glas et al .: Granat . In: Christian Weise (ed.): ExtraLapis . tape 9 . Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 13 .
  29. Maximilian Glas et al .: Granat . In: Christian Weise (ed.): ExtraLapis . tape 9 . Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 9 .
  30. ^ Frank S. Spear: Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths . 2nd Edition. Mineralogical Society of America, 1993, ISBN 978-0-939950-34-8 , Metamorphism of pelites, pp. 337-391 (English).
  31. Mindat - Number of localities for almandine
  32. Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 196 ( Dörfler Natur ).
  33. a b List of places where almandine was found in the Mineralienatlas and Mindat
  34. ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 120 .
  35. Bernhard brother embellished stones . Neue Erde Verlag, 2005, ISBN 3-89060-025-5 , p. 68 .
  36. Jaroslav Bauer, Vladimír Bouška, František Tvrz: Gemstone Guide . Verlag Werner Dausien, Hanau / Main 1993, ISBN 3-7684-2206-2 , p. 102 .