Hydromagnesite

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Hydromagnesite
Hydromagnesite.png
Hydromagnesite
General and classification
other names
  • Magnesia alba or light magnesia
  • Talkjord hydrate or talc hydrate
chemical formula Mg 5 (CO 3 ) 4 (OH) 2 · 4H 2 O
Mineral class
(and possibly department) 		Carbonates
System no. to Strunz
and to Dana 		05.DA.05 ( 8th edition : V / E.01)
16b.07.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 10.11  Å ; b  = 8.95 Å; c  = 8.38 Å
β  = 114.4 °
Formula units Z  = 2
Twinning lamellar after {100}
Physical Properties
Mohs hardness 3.5
Density (g / cm 3 ) measured: 2.24 to 2.25; calculated: 2.25
Cleavage completely after {010}
Break ; Tenacity uneven
colour colorless, white
Line color White
transparency transparent to translucent
shine Glass gloss, silk gloss, pearl gloss
Crystal optics
Refractive indices n α  = 1.523
n β  = 1.527
n γ  = 1.545
Birefringence δ = 0.022
Optical character biaxial positive
Axis angle 2V = 30 to 90 ° (measured); 52 ° (calculated)
Other properties
Special features Fluorescence in UV light: short-wave, green; long-wave, blue-white

Hydromagnesite (also magnesia alba or light magnesia ) is a rather seldom occurring mineral from the mineral class of " carbonates and nitrates ". It crystallizes in the monoclinic crystal system with the composition Mg 5 (CO 3 ) 4 (OH) 2 · 4H 2 O, so from a chemical point of view it is a water-containing magnesium carbonate with hydroxide ions as additional anions .

Hydromagnesite is transparent to translucent and only develops small, needle-like to tabular crystals , which are usually arranged in tufted aggregates. Often, however, it also forms massive aggregates and crusty coatings. The surfaces of the colorless to white crystals have a glass-like sheen . In aggregate form or crusts, however, the mineral shimmers more like mother-of-pearl or is matt.

Etymology and history

Hydromagnesite was first discovered at Castle Point near Hoboken in the US state of New Jersey. It was analyzed and described in 1827 by Hans Gabriel Trolle-Wachtmeister (1782–1871) under the name Magnesia alba (or Talkjordshydrat , German: Talkerdehydrat ). In the opinion of Franz von Kobell , however, this designation was of little importance and also inappropriate in the mineralogical nomenclature. He therefore suggested the name hydromagnesite - a compound made-up word from the Greek word “hydro” for water and magnesite - to emphasize the difference between magnesite and anhydrous talc earth carbonate .

classification

In the 8th edition of the mineral systematics according to Strunz , which is now outdated but still in use , the hydromagnesite belonged to the department of “Hydrous carbonates with foreign anions ”, where together with Artinit it formed the “hydromagnesite-artinite group” with the system no. V / E.01 and the other members Brugnatellite , Chlorartinit , Coalingit , Dypingit , Giorgiosit , indigirite and Widgiemoolthalith formed.

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 assigns hydromagnesite to the category of “carbonates with additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found in the sub-section “With medium-sized cations” according to its composition, where the “hydromagnesite group” with the system no. 5.DA.05 and the other members Dypingit, Giorgiosit and Widgiemoolthalith.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns hydromagnesite to the more finely divided division of "carbonates - hydroxyl or halogen". Here he can only be found together with Widgiemoolthalith in the unnamed group 16b.07.01 .

Crystal structure

Hydromagnesite crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 10.11  Å ; b  = 8.95 Å; c  = 8.38 Å and β = 114.4 ° and 2 formula units per unit cell . Template: room group / 14

properties

Above about 200 ° C, hydromagnesite decomposes with the release of water and carbon dioxide. What remains is magnesium oxide .

Education and Locations

Hydromagnesite tufts on light green magnesite . The green color of the magnesite results from nickel impurities. Location: Cedar Hill Quarry, Fulton Township, Lancaster County, Pennsylvania . Size: 7.3 × 5.5 × 3.1 cm
Hydromagnesite, location: Red Mountain near Santa Clara , California / USA

Hydromagnesite is a weathering product of magnesium-containing minerals ( brucite , serpentine ) or rocks ( ultramafitite , dolomite , marble ). In dolomite and marble, it can be the result of a hydrothermal transformation of the corresponding rocks. Hydromagnesite typically occurs as encrustations or the filling of crevices and cavities.

Furthermore, hydromagnesite occurs in (limestone) caves as a speleothem or as so-called moon milk . Here it is formed by seepage water rich in magnesium. After calcite and aragonite , it is the most common speleothemic mineral.

A special feature is that hydromagnesite, similar to calcite and aragonite, is also formed by living organisms. It is known that stromatolites precipitate hydromagnesite under alkaline conditions (pH> 9) ( Lake Salda , southern Turkey ). Formation by microorganisms is also known from Dry Lake in British Columbia .

As a rather rare mineral formation, hydromagnesite can sometimes be abundant at different sites, but overall it is not very common. So far (as of 2012) around 280 sites are known to be known. In addition to its type locality Castle Point near Hoboken in New Jersey, the mineral occurred in the United States of America in the "Nautiloid Canyon" (part of the Grand Canyon ) in Arizona, in many places in California , in several pits near Georgetown (Colorado ) , in the "Marengo Cave" in Crawford County (Indiana) , at White Pine in Ontonagon County of Michigan, at Kings Mountain in North Carolina, Pennsylvania , at Lime Rock in Rhode Island and in several locations in Maryland , Nevada , New Mexico , New York , South Dakota , Tennessee , Utah , Virginia , Washington, and Wisconsin .

In Germany Hydromagnesit was previously at the quarry Limberg in the town of Sasbach in Baden-Wuerttemberg, in the yew grotto near Bamberg and at Zeilberg in Bavaria, several Fund points in Stolberg (Rheinland) and Hüsten (Arnsberg) in North Rhine-Westphalia and the Arensberg , Ettringer Bellerberg in the Eifel and in the Friedrichssegen mine in the Lahn valley in Rhineland-Palatinate.

In Austria, the mineral was found in the serpentinite quarry near Griesserhof (Gulitzen) near Hirt in the Friesach - Hüttenberg district and on Buchberg near Sankt Veit an der Glan in Carinthia, near Loja in the Lower Austrian municipality of Persenbeug-Gottsdorf , on Untersberg in Salzburg , on the Eibegggraben ( Fischbacher Alps ), near Fohnsdorf and Kraubath an der Mur in Styria, on the Gumpachkreuz in Hinterbichler Dorfertal and on the Gratlspitze in Tyrol and near Obertraun in Upper Austria.

In Switzerland, hydromagnesite has so far only occurred at Selva ( Tujetsch ) in the canton of Graubünden, in the salt mine near Bex in the canton of Vaud and in the Les Moulins mine near Saint-Luc VS in the canton of Valais.

Other locations include the Antarctic, Australia, Belgium, Bolivia, Brazil, China, France, Greece, Iran, Israel, Italy, Japan, Canada, Morocco, Mexico, Mongolia, New Zealand, Norway, Romania, Russia, Sweden , Serbia, Zimbabwe, Slovakia, Spain, South Africa, Czech Republic, Turkey, Turkmenistan, Hungary, Uzbekistan and the United Kingdom (Great Britain).

use

Hydromagnesite is industrially processed together with huntite into inorganic flame retardants .

Hydromagnesite has the property of endothermic decomposition under thermal stress releasing water and carbon dioxide. This prevents the fire from spreading when used in plastics.

Magnesium oxide remains as a solid decomposition product . The decomposition begins at a temperature of 200 ° C for flame retardants, which is an advantage over other flame retardants such as aluminum hydroxide .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X .
  2. ↑ Webmineral - Hydromagnesite
  3. ^ A b John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Hydromagnesite , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 66.8 kB )
  4. ↑ a b c d Mindat - hydromagnesite
  5. ^ Project Runeberg - Nordisk familjebok: Hydromagnesit , p. 1465
  6. ↑ JC Deelman (2011): Low-temperature formation of dolomite and magnesite. Chapter Six: Magnesite & Huntite ( PDF 223.8 kB ; Magnesia alba and Hydromagnesite , pp. 18-21)
  7. ↑ Fr. von Kobell: About the hydromagnesite from Kumi on Negroponte , in: Journal for practical chemistry , Volume 4, Leipzig 1835 in the Google book search
  8. ↑ a b LA Hollingbery, TR Hull: The Thermal Decomposition of Huntite and Hydromagnesite - A Review , in: Thermochimica Acta , Volume 509 (2010), pp. 1–11 ( PDF 1.11 MB ( Memento from July 18, 2011 in Internet Archive ))
  9. ↑ CJR Braithwaite, Veysel Zedef, Living hydromagnesite stromatolites from Turkey, Sedimentary Geology, Volume 106, Issues 3-4, November 1996, Page 309, doi : 10.1016 / 0037-0738 (94) 90051-5
  10. ↑ Robin W. Renaut, Douglas Stead: Recent Magnesite-Hydromagnesite sedimentation in Playa Basins of the Cariboo Plateau , British Columbia Geologic Survey ( Memento of November 22, 2004 in the Internet Archive ) (PDF; 1.2 MB)
  11. ↑ a b Mindat - localities for hydromagnesite
  12. ↑ LA Hollingbery, TR Hull: The Fire Retardant Behavior of Huntite and Hydromagnesite - A Review , in: Polymer Degradation and Stability , Volume 95 (2010), pp. 2223-225 ( PDF 1.11 MB ( Memento from July 18, 2011 in the Internet Archive ))
  13. ^ R. Rothon: Particulate-Filled Polymer Composites , 2nd edition 2003