Magnesite

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Magnesite
Magnesite-121892.jpg
Magnesite from the Serra das Éguas, Brumado , Bahia , Brazil (size: 11.4 × 9.2 × 3.6 cm)
General and classification
other names

Bitter spar

chemical formula Mg [CO 3 ]
Mineral class
(and possibly department) 		Carbonates and nitrates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		5.AB.05 ( 8th edition : Vb / A.02)
01/14/01/02
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3  2 / m
Space group R 3 c (No. 167)Template: room group / 167
Lattice parameters a  = 4.63  Å ; c  = 15.03 Å
Formula units Z  = 6
Physical Properties
Mohs hardness 3.5 to 4.5
Density (g / cm 3 ) measured: 3.00 (2); calculated: 3.010
Cleavage completely according to {10 1 1}
Break ; Tenacity clamshell; brittle
colour colorless, white, yellowish, brownish to black
Line color White
transparency transparent to opaque
shine Glass gloss, matt
Crystal optics
Refractive indices n ω  = 1.700
n ε  = 1.509
Birefringence δ = 0.191
Optical character uniaxial negative

Magnesite , also known as bitter spar , is a frequently occurring mineral from the mineral class of " carbonates and nitrates " with the chemical composition Mg [CO 3 ] and is therefore a magnesium carbonate in chemical terms .

Magnesite crystallizes in the trigonal crystal system and develops rhombohedral , prismatic crystals , but also earthy, massive aggregates in white, yellowish, brownish to black color. Colorless crystals are also known.

With the iron spar siderite , magnesite forms a continuous row of mixed crystals .

Etymology and history

The mineral was first discovered in 1803 by D. Mitchel in Moravia and described by Abraham Gottlob Werner , who called the snowy to reddish-white, earthy-coarse fragments “pure talc earth” ( Talcum carbonatum , native magnesia carbonatee ).

Its name, magnesite , which is still valid today, after its metallic component magnesium , was given to the mineral in 1808 by Dietrich Ludwig Gustav Karsten .

classification

In the outdated 8th edition of the mineral classification according to Strunz , magnesite belonged to the common mineral class of "carbonates, nitrates and borates" and there to the department of "anhydrous carbonates without foreign anions ", where it belongs together with calcite , gaspéit , otavite , rhodochrosite , siderite , Smithsonite and spherocobaltite as well as in the appendix with vaterite the "calcite group" with the system no. Vb / A.02 formed.

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. V / B.02-30 . In the "Lapis system" this also corresponds to the section "Anhydrous carbonates [CO 3 ] 2- without foreign anions", where magnesite together with calcite, gaspéit, otavite, rhodochrosite, siderite, smithsonite, spherocobaltite and vaterite form the group "calcite Group "forms (as of 2018).

The 9th edition of Strunz's mineral systematics , valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns magnesite to the newly defined class of "carbonates and nitrates" (the borates form a separate class here), but there also in the section of “carbonates without additional anions; without H 2 O “. This is, however, further subdivided according to the affiliation of the cations involved to certain element groups , so that the mineral can be found according to its composition in the subsection "alkaline earth (and other M 2 +) carbonates", where it is again in the "calcite group" the system no. 5.AB.05 is classified.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns magnesite to the common class of "carbonates, nitrates and borates" and there in the department of "anhydrous carbonates", like the outdated Strunz system. Here, too, it is in the "Calcite group (trigonal: R 3 c )" with the system no. 01/14/01 to be found in the subsection “ Anhydrous carbonates with simple formula A + CO 3 ”. Template: room group / 167

Chemism

The theoretical composition of magnesite (Mg [CO 3 ]) consists of 28.83% magnesium , 14.25% carbon and 56.93% oxygen . Due to the mixed crystal formation with siderite, however, it usually contains iron , which partly replaces the magnesium in the formula . Small additions of manganese and calcium were also observed.

Crystal structure

Magnesite crystallizes isotypically with calcite in the trigonal crystal system in the space group R 3 c (space group no. 167) with the lattice parameters a  = 4.63  Å and c  = 15.03 Å and six formula units per unit cell . Template: room group / 167

properties

Like most carbonates, magnesite is soluble in acids with the release of CO 2 . Compared to calcite , however, it only dissolves in powder form in warm acids.

Modifications and varieties

Breunnerite from Bolzano, Italy
Pinolite or "ice flower" magnesite from the Tauern (Austria)

Due to its complete mixed crystal formation with siderite (Fe [CO 3 ]), individual phase areas were divided up similar to the plagioclase in the feldspars and given individual names. The end link magnesite may contain up to 10 mol% Fe [CO 3 ] and vice versa the siderite up to 10  mol% Mg [CO 3 ]. The pontics are 10–30 mol% Fe [CO 3 ] as breunnerite , 30–50 mol% Fe [CO 3 ] as mesitin spar , 50–70 mol% Fe [CO 3 ] as pistomesite and 70 -90 mol% Fe [CO 3 ] referred to as sideroplesite .

In addition, magnesites are also often referred to as crystal magnesite (also spat or pinolite (h) magnesite or pinolite for short and outdated pinolenstein ) and in microcrystalline form as gel magnesite, depending on their crystal development in macrocrystalline form .

The often misleading abbreviation pinolite (also called pinolite stone or marbel stone ) is also used for a mineral mixture of magnesite, dolomite and graphite . The matrix consists of dolomite pigmented light gray to almost black with graphite and contains inclusions of white magnesite grains that look like pine nuts ( Pinoli ). Due to the often flower-like structure of the magnesite deposits, pinolite is also known as ice flower magnesite .

As Hoshiit (also Choschiit ) designated Yue-Chu Siang, Fuo Kuo-Fun and S. Chen-Ea 1964, a nickel-containing variety, having the formula (Ni, Mg) [CO 3 ] 2 . The mineral was discovered in the form of green, fine-grained masses in the oxidation zone of nickel-containing copper sulfide deposits in China . When the new minerals and mineral names were announced in 1965, the brief description of the Hoshiit already contained the comment that this variety should not be named, but that the name could be used if a mineral with a higher nickel than magnesium content was discovered. With the mass discrediting in 2006 by the Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association (IMA), Honshiit was also discredited as an unrecognized mineral and thus an invalid mineral name.

Education and Locations

Magnesite (golden brown) and dolomite (white) from the Azcárate quarry, Eugui , Esteríbar , Navarra, Spain (size: 10.2 cm × 6.7 cm)

Magnesite forms predominantly hydrothermally , metasomatically or metamorphically . Occasionally, however, it is also found in igneous rocks . Spat or pinolite magnesites are mainly formed in talc and chlorite schists , as well as in dolomite rocks . Dense magnesite, which is initially similar to opal in a gel-like texture, but later changes into a microcrystalline structure, is more likely to be found in serpentine stones .

Crystals up to one meter in size have already been found in the dolomite rock in Brumado and Bahia (Brazil). Usually, however, the crystal sizes are in the centimeter range.

Other locations include Nangarhar in Afghanistan; Central and Eastern Egypt ; Biskra in Algeria; Princess Elizabeth Land in East Antarctica; Salta in Argentina; Gegharkunik in Armenia; Ethiopia ; several regions in Australia ; Department of Cochabamba in Bolivia; the Antofagasta and Atacama regions in Chile; several provinces in the People's Republic of China ; Baden-Württemberg , Bavaria , Hesse , Rhineland-Palatinate , Saxony-Anhalt , Saxony and Thuringia in Germany; several regions in France ; Finland ; some provinces in Greece ; Kitaa in Greenland; Java (island) in Indonesia; different regions in Italy ; Honshū and Shikoku in Japan; several regions in Canada ; Kazakhstan ; Katanga in the Democratic Republic of the Congo; Korea ; Madagascar ; Mexico ; Nepal ; several regions in Norway ; many regions in Austria ; Eugui in Spain; Slovakia ; Bohemia and Moravia in the Czech Republic; Borsod-Abaúj-Zemplén and Pest in Hungary; as well as many regions of the United States .

use

massive magnesite as raw and tumbled stone

As a raw material

Due to its high temperature resistance up to around 3000 ° C, magnesite is an important raw material for the production of refractory sintered magnesite bricks, which are used to line blast furnaces , converters for steelmaking and other melting furnaces. The bricks are fired in kilns at high temperatures of up to around 1800 ° C , which creates crystalline magnesium oxide (MgO). In addition, these bricks have good heat storage properties , so that they are used as storage cores in night storage heaters and electric fireplaces .

If magnesite is burned at lower temperatures of up to around 800 ° C, some of it remains as carbonate, which means that the stoichiometrically possible amount of carbon dioxide (CO 2 ) is not given off. The resulting “ caustic magnesia” remains reactive and is mixed with fillers to make Sorel cement and used to manufacture refractory building materials and insulating compounds.

The thermal decomposition behavior of the magnesite is determined by the different properties of the raw material, the process technology used and the physical and chemical processes.

As a gem

Different colored magnesite beads

With a Mohs hardness of 4 to 4.5, magnesite is actually too soft for commercial use as a gemstone . A clear, faceted magnesite has a certain value among collectors.

The mineral, like howlite, which is similar in appearance, serves as the basis for imitating turquoise . Colored blue and stabilized to protect against damage , the coveted and expensive matrix turquoise can be imitated, which is often sold under the name turkenite . However, magnesite generally accepts colors well and can therefore be colored very differently.

Under the misleading trade name lemon chrysoprase (also lemon chrysoprase ), a light- to yellow-green mixture of magnesite and chrysoprase is known, whereby the chrysoprase content can go to zero in poor quality and the material is correctly referred to as lemon magnesite (also lemon magnesite ) would have to be.

See also

literature

  • Christian Friedrich Ludwig: Handbook of Mineralogy after AG Werner . tape 2 . Siegfried Lebrecht Crusius, Leipzig 1804, p. 154 ( limited preview in Google Book search).
  • Dietrich Ludwig Gustav Karsten: Mineralogical tables with consideration of the latest discoveries . 2nd, improved and increased edition. Heinrich August Rottmann, Berlin 1808, p. 48, 93 ( limited preview in Google Book search and limited preview in Google Book search).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 113 .

Web links

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

Individual evidence

  1. ^ A b c d e Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  515-519 .
  2. ^ A b David Barthelmy: Magnesite Mineral Data. In: webmineral.com. Retrieved December 21, 2019 .
  3. ^ A b c 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.  286 (English).
  4. ↑ a b c d e magnesite . 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; 67  kB ; accessed on December 21, 2019]).
  5. ↑ a b c magnesite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 21, 2019 .
  6. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  7. ↑ Dietrich Ludwig Gustav Karsten: Mineralogical tables with consideration of the latest discoveries . 2nd, improved and increased edition. Heinrich August Rottmann, Berlin 1808, p. 93 ( limited preview in Google Book search - itemization 62).
  8. ^ Christian Friedrich Ludwig: Handbook of Mineralogy after AG Werner . tape 2 . Siegfried Lebrecht Crusius, Leipzig 1804, p. 154 ( limited preview in Google Book search).
  9. ↑ Dietrich Ludwig Gustav Karsten: Mineralogical tables with consideration of the latest discoveries . 2nd, improved and increased edition. Heinrich August Rottmann, Berlin 1808, p. 48 ( limited preview in the Google book search - I. Earth and stone types. 6. The bitter earth. Magnesite. Pure talc earth).
  10. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed December 21, 2019 .
  11. ↑ a b Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  701 .
  12. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  569 (first edition: 1891).
  13. ↑ Mineral Atlas : Pinolite
  14. ↑ Pinolite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 21, 2019 .
  15. ^ Carl Hintze: New minerals and new mineral names . In: Karl F. Chudoba (Ed.): Handbuch der Mineralogie . Supplementary volume 111.Walter De Gruyter & Co., Berlin 1968, p. 537 ( limited preview in Google Book search).
  16. ↑ Yue Chu-Siang, Fuo Kuo-Fun and S. Chen-Ea: Hoshiite, NiMg (CO 3 ) 2 , a new mineral . In: Acta Geologica Sinica . tape 44 , no. 2 , 1964, p. 213-218 .
  17. ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  702 .
  18. ↑ Michael Fleischer : New Mineral Names . In: American Mineralogist . tape  50 , 1965, pp. 2096–2111 (English, rruff.info [PDF; 1.3 MB ; Retrieved December 21, 2019] Hoshiite p. 2100).
  19. ↑ Ernst AJ Burke: A Mass Discreditation of GQN Minerals . In: The Canadian Mineralogist . tape 44 , 2006, pp. 1557–1560 (English, rruff.info [PDF; 119 kB ; accessed on December 21, 2019]).
  20. ↑ List of locations for magnesite in the Mineralienatlas and Mindat , accessed on December 21, 2019.
  21. ↑ a b Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 63-64 .
  22. ↑ Peter Zährer: Electric fireplaces as day or night electricity heating . In: der-kachelofen.com. Retrieved December 21, 2019 .
  23. ↑ Eckehard Specht, Hartmut Kainer, Rudolf Jeschar: The reaction, pore diffusion and thermal conductivity coefficients of various magnesites and their influence on the decomposition time . Radex-Rundschau, Radenthein 1986, p. 248-268 .
  24. ^ 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. 230 .
  25. ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 71 .
  26. ↑ Name search - trade names and what they mean. In: epigem.de. EPI - Institute for Gemstone Testing, accessed on December 21, 2019 (entry of lemon chrysoprase required).
  27. ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 60 .