Anhydrite

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Anhydrite
Anhydrite-261625.jpg
Anhydrite from Naica , Municipio de Saucillo, Chihuahua, Mexico (size 16.8 cm × 15.4 cm × 10.8 cm)
General and classification
other names
  • Anhydrite spar
  • Gekrösstein
  • Karstenite
  • Muriacite
chemical formula Ca [SO 4 ]
Mineral class
(and possibly department) 		Sulfates (and relatives)
System no. to Strunz
and to Dana 		7.AD.30 ( 8th edition : VI / A.07)
03/28/02/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Amma (No. 63, Position 3)Template: room group / 63.3
Lattice parameters a  = 6.99  Å ; b  = 7.00 Å; c  = 6.24 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 3 to 3.5
Density (g / cm 3 ) measured: 2.98; calculated: 2.95
Cleavage completely after {010}, almost completely after {100}, good after {001}
Break ; Tenacity uneven to splintery; brittle
colour colorless to white; more rarely light blue, light purple to pink, reddish, light brown, gray
Line color White
transparency transparent to translucent
shine Glass gloss, mother-of-pearl, greasy gloss
Crystal optics
Refractive indices n α  = 1.567 to 1.574
n β  = 1.574 to 1.579
n γ  = 1.609 to 1.618
Birefringence δ = 0.042 to 0.044
Optical character biaxial positive
Axis angle 2V = measured: 36 ° to 45 °; calculated: 44 °
Pleochroism Visible: With violet colored material
X = colorless to very light yellow or pink; Y = light violet or rose; Z = violet
Other properties
Chemical behavior hardly soluble in water (2 g / l at 25 ° C)

Anhydrite , also known as anhydrite spar , is a frequently occurring mineral from the mineral class of " sulfates ( and relatives )" with the chemical composition Ca [SO 4 ] and thus, chemically speaking, calcium sulfate .

Anhydrite crystallizes in the orthorhombic crystal system and develops mostly coarse-grained, massive aggregates , but also cubic and prismatic crystals up to about 20 cm in size. In its pure form, anhydrite is transparent and colorless. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also be translucent white and, due to foreign admixtures, take on a bluish, reddish, violet or brown color. The line color of anhydrite, however, is always white. Visible crystal surfaces have a glass-like sheen , lamellar or granular aggregates, on the other hand, have a mother-of-pearl to oily sheen.

With a Mohs hardness of 3 to 3.5, anhydrite is one of the medium-hard minerals that can be scratched with a copper coin. Its density of around 3 g / cm 3 corresponds to that of cement .

Mostly consisting of the mineral anhydrite, i.e. mono-mineral rocks with only minor admixtures of other minerals such as quartz or clay minerals, are also referred to as anhydrite or anhydrite stone. On or near the surface of the earth, however, they are often swollen to gypsum due to contact with water .

Etymology and history

The mineral was first discovered in 1794 by Nicolaus Poda von Neuhaus , who called it Muriacite , who mistakenly believed that it was hydrochloric lime and contained hydrochloric acid ( acidum muriaticum ):

"This same Mr. Abbé Poda recently discovered a new type of lime, which he calls muriacite according to its constituent parts hydrochloric acid lime, or according to the current method of baptizing new fossils, because it consists of calcareous earth, hydrochloric acid, and water."

- Johann Ehrenreich von Fichtel

However, later analyzes could prove that it was sulfuric acid lime , i.e. anhydrous calcium sulfate . The French mineralogist René-Just Haüy named the mineral in 1801 as chaux sulfatée anhydre (German: anhydrous sulfate lime ) after this property . Martin Heinrich Klaproth also confirmed in 1803 that the mineral, erroneously called muriacite , did not contain any hydrochloric acid, as it was not clouded by silver nitrate ( nitric acid silver solution ). Klaproth, however, left it to the mineralogists with voting rights to either keep the name Muriacit or to adopt the name anhydrite coined by BR Werner.

The name anhydrite, which is still valid today, was finally coined a year later by Abraham Gottlob Werner in his Handbuch der Mineralogie .

The type localities are the salt mine near Hall in Tirol in Austria and the potash plant near Leopoldshall in Germany.

The type material of the mineral is available at the Technical University Bergakademie Freiberg in Germany under catalog no. 16538 kept.

classification

Already in the outdated, but still in use 8th edition of the mineral classification according to Strunz , the anhydrite belonged to the mineral class of "sulfates, selenates, tellurates, chromates, molybdates, tungstates" and there to the department of "anhydrous sulfates without foreign anions ", where it belongs together with aphthitalite ( glaserite ) the "glaserite anhydrite group" with the system no. VI / A.07 and the other members glauberite , kalistrontite and palmierite .

In the "Lapis mineral directory", which was last updated in 2018 and which, out of consideration for private collectors and institutional collections, is still based on this classic systematics by Karl Hugo Strunz , anhydrite was given the system and mineral no. VI / A.08-50 . In the "Lapis system" this corresponds to the section "Anhydrous sulfates [SO 4 ] 2- , without foreign anions", where the mineral, together with aphthitalite, bubnovaite , glauberite, ivsite , kalistrontite, Möhnite and palmierite, is an independent but unnamed group forms.

The 9th edition of Strunz's mineral systematics , valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns anhydrite to the class of "sulfates (selenates, tellurates, chromates, molybdates and wolframates)" and there into the department the "sulfates (selenates etc.) without additional anions, without H 2 O". However, this section is further subdivided according to the size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With only large cations”, where it is the only member of the unnamed group 7.AD.30 .

The systematics of minerals according to Dana also assigns the anhydrite to the class of "sulfates, chromates and molybdates" and there into the category of "sulfates". Here he is the only member of the unnamed group 28.03.02 within the subdivision of " Anhydrous acids and sulfates (A 2+ ) XO 4 ".

Crystal structure

Crystal structure of anhydrite
__ Ca     __ S     __ O

Anhydrite crystallizes orthorhombically in the space group Amma (space group no. 63, position 3) with the lattice parameters a  = 6.99  Å ; b  = 7.00 Å and c  = 6.24 Å and 4 formula units per unit cell . Template: room group / 63.3

In the crystal structure of anhydrite, the calcium atoms are each surrounded by a total of 8 oxygen atoms, which form a trigonododecahedron . Parallel to the z-axis [001], alternating, edge-linked dodecahedra and [SO 4 ] tetrahedron stable chains are formed in the sequence . The edge-linked dodecahedra also form chains parallel to the a-axis [100] and chains parallel to the b-axis [010] via common corners.

properties

Anhydrite crystals in the bedrock with clearly recognizable cleavage surfaces
Anhydrite crystals in thin section with crossed polarizers with the typical rather pale interference colors

Anhydrite crystals are easily cleavable and therefore often have three cleavage surfaces at right angles to one another. This allows them to be distinguished from the otherwise very similar gypsum crystals.

If anhydrite is permanently exposed to moisture, it absorbs water and turns into gypsum. This storage of crystal water can increase the volume by more than 50%. This increase in volume of an anhydrite body in the subsoil, also known as swelling, can break through to the surface of the earth and possibly cause damage to buildings there, as in the case of the uplift cracks in Staufen im Breisgau .

In mining, swelling anhydrite layers can narrow the tunnels ( dwarf holes , swelling caves ) and blow up the adjacent rock. The same applies to tunnel construction, such as the Adlertunnel (CH), Engelberg Tunnel , Weinsberger Tunnel or the Stuttgart 21 tunnels , some of which run through anhydrite layers .

Pure anhydrite is therefore not suitable as a building material .

Modifications and varieties

  • Angelit is the trade name for a fine-grained and translucent, gray-blue-violet anhydrite aggregate.
  • As Vulpinit grained anhydrite is aggregate referred.

Education and Locations

White, spherical anhydrite as an inclusion in halite from Poland

Anhydrite is a rock-forming mineral. As such, it is found in sedimentary sequences of evaporites , in which it mostly arose from the diagenetic dehydration of gypsum, which in turn precipitated from salt-saturated seawater . Anhydrite can only be precipitated directly at water temperatures of more than 35 ° C, which is usually only possible in the tidal range . In evaporites, anhydrite mostly occurs either with calcite , dolomite and gypsum or with gypsum and halite . Less common accompanying minerals include celestine , magnesite , polyhalite , sylvine and sulfur .

As a frequent mineral formation, anhydrite can be found at many localities, whereby so far (as of 2015) around 1400 localities are known. Noteworthy due to extraordinary crystal finds are among others Naica in Chihuahua (Mexico), in which drusen with up to 20 cm long anhydrite crystals were found, and Wieliczka in Poland, where up to 2 cm large crystals were found.

In Germany, anhydrite occurs in the Black Forest , near Heilbronn , Müllheim and the Swabian Alb in Baden-Württemberg; in Franconia and Upper Bavaria ; at many places in Hesse and Lower Saxony ; near Aachen , Rheinberg and in the Sauerland in North Rhine-Westphalia; in the Rhineland-Palatinate Eifel ; near Saarbrücken and Saarlouis in Saarland; in the Harz from Lower Saxony to Thuringia (e.g. Kohnstein ); in the Ore Mountains and near Zwickau in Saxony; near Bad Segeberg in Schleswig-Holstein as well as near Gera , in Kyffhäuser and in the Thuringian Forest .

In Austria, the mineral can be found near Pöttsching in Burgenland, in the Gailtal Alps and the Carnic Alps in Carinthia, at Semmering in Lower Austria, in several places in Salzburg and Styria , in North Tyrol and in Upper Austria .

In Switzerland, anhydrite was found in several places in the canton of Valais , at Felsenau / Leuggern and Schafisheim in the canton of Aargau, at Leissigen in the canton of Bern, in the Graubündner valleys Val Cristallina and Val Milà , at Airolo and Lavorgo in Ticino, in the salt and water regions Sulfur mines near Bex and Sublin in the canton of Vaud as well as in several places during the construction of the Gotthard tunnel .

Other locations are in Afghanistan , Egypt , Algeria , Argentina , Armenia , Australia , Bolivia , Brazil , Bulgaria , Chile , China , Denmark , Ecuador , France , Greece , Guatemala , Indonesia , Iran , Ireland , Iceland , Israel , Italy , Japan , Canada , Kazakhstan , Qatar , Colombia , Democratic Republic of the Congo , Cuba , Lithuania , Madagascar , Malta , Morocco , Mexico , Mongolia , Namibia , New Zealand , Netherlands , Norway , Pakistan , Panama , Papua New Guinea , Peru , the Philippines , Romania , Russia , Saudi Arabia , Sweden , Serbia , Zimbabwe , Slovakia , Slovenia , Spain , South Africa , Taiwan , Thailand , Czech Republic , Tunisia , Turkey , Ukraine , Hungary , Uzbekistan , the United Kingdom , the United States of America .

Anhydrite could also be found in rock samples from the Mid-Atlantic Ridge , the Central Indian Ridge , the Bismarck Sea , the Chinese Sea and the East Pacific Ridge as well as outside the earth on the moon (Mare Crisium).

Anhydrite can also be produced by burning plaster of paris. At temperatures around 100 ° C, some water of crystallization remains in the gypsum stone, which creates hemihydrate; At higher temperatures all of the water of crystallization is withdrawn and anhydrite is formed.

use

Angelite rough stone

Mixed with aggregates ( aggregate ), anhydrite is used as a screed . Wood concrete is obtained by adding sawdust .

Powdered anhydrite is processed into adhesive for tiles, but a “stimulator”, usually potassium sulfate (K 2 SO 4 ) or calcium oxide (CaO), must be added. The stimulator, the proportion of which is 3–15%, accelerates water retention, which converts anhydrite to gypsum. The conversion of anhydrite to gypsum only takes place to about 65%, whereby the gypsum ensures the quick drying and the anhydrite as a framework for the high strength. Such anhydrite binders are air-hardening, non-hydraulic binders made from natural or synthetic anhydrite. Their physical and chemical properties are comparable to plaster of paris. Calcium sulphate binder is used, for example, in residential construction for the production of calcium sulphate screed or calcium sulphate flowing screed.

Powdered anhydrite is a component of cement and is also used in the production of sulfuric acid and aerated concrete .

The gray-blue- violet -colored variety, known under the trade name Angelit , is used as a gemstone and is usually processed into various pieces of jewelry in the form of hand flatterers and ground into cabochons and spherical beads. Since the stone has only a low hardness ( Mohs hardness 3 to 3.5) and also shows a high tendency to split, it is stabilized with synthetic resin to protect it from damage.

See also

literature

Web links

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

Individual evidence

  1. ↑ David Barthelmy: Anhydrite Mineral Data. In: webmineral.com. Retrieved April 29, 2019 .
  2. ↑ a b c d 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.  369 .
  3. ↑ a b c d e anhydrite . 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; 68  kB ; accessed on April 29, 2019]).
  4. ↑ a b c 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 .
  5. ↑ a b c d e f anhydrite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 29, 2019 .
  6. ↑ a b Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 137 .
  7. ↑ Sedimentary rocks - anhydrite / gypsum stone. State Geological Services of Germany / Federal Institute for Geosciences and Raw Materials: Natural resources of the Federal Republic of Germany, archived from the original on February 19, 2015 ; accessed on April 29, 2019 .
  8. ↑ TO Poda: From the Lilalith . In: Johann Ehrenreich von Fichtel (Ed.): Mineralogical essays . Mathias Andreas Schmidt, imperial and royal book printer, Vienna 1794, p. 228 , footnote *) ( available online at rruff.info [PDF; 277 kB ; accessed on May 6, 2019]).
  9. ↑ 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.  171 .
  10. ^ René-Just Haüy : IV. Chaux sulfatée anhydre, c'est-à-dire, privée d'eau . In: Traité de Minéralogie . tape  4 , 1801, p. 348–353 (French, available online at rruff.info [PDF; 703 kB ; accessed on May 6, 2019]).
  11. ↑ Martin Heinrich Klaproth : Chemical investigation of Muriacit . In: New General Journal of Chemistry . tape  2 , no. 4 , 1803, p. 355–362 ( available online at rruff.info [PDF; 254 kB ; accessed on May 6, 2019]).
  12. ^ Christian Friedrich Ludwig: VI: Kalk sex. D. Vitriolic acid lime genera. 126. Anhydrite . In: Handbook of Mineralogy according to AG Werner . tape 2 . Siegfried Lebrecht Crusius, Leipzig 1804, p. 209-212 .
  13. ↑ Catalog of Type Mineral Specimens - Anhydrite. (PDF 84 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed May 7, 2019 .
  14. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  15. ↑ Christof Wagner: Risse in Staufen: Pumping, Repairing and Hope. badische-zeitung.de, October 15, 2010, accessed on April 29, 2019 .
  16. ↑ Regine Ounas-Kräusel: Work is going on inside the mountain. badische-zeitung.de, October 14, 2010, accessed on April 29, 2019 .
  17. ↑ Michael Schmidt: Restoration of millions as a greeting to Stuttgart 21. (No longer available online.) Stuttgarter Nachrichten, August 21, 2010, archived from the original on September 20, 2017 ; accessed on March 30, 2018 .
  18. ↑ Claus Hecking, Gerald Traufetter: Expensive Railway Project: Week of Truth for Stuttgart 21. Spiegel Online, December 12, 2017, accessed on April 29, 2019 .
  19. ↑ Name search - trade names and what they mean. In: EPI Institute for Gemstone Testing. epigem.de, accessed on April 29, 2019 ( Angelit input required).
  20. ↑ Angelite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 29, 2019 .
  21. ↑ Localities for Anhydrite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 29, 2019 .
  22. ↑ a b List of sites for anhydrite in the Mineralienatlas and Mindat
  23. ↑ Angelit mineral profile. In: steine-und-minerale.de. Stones and Minerals, December 4, 2018, accessed April 29, 2019 .