Periclase

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Periclase
Periclase - Ronneburg, Thuringia1.jpg
White to light green periclase with black srebrodolskite from Ronneburg (Thuringia) (image width 5 mm)
General and classification
other names
chemical formula MgO
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.AB.25 ( 8th edition : IV / A.04)
02/04/01/01
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fm 3 m (No. 225)Template: room group / 225
Lattice parameters a  = 4.21  Å
Formula units Z  = 4
Physical Properties
Mohs hardness 5.5
Density (g / cm 3 ) measured: 3.56 to 3.68; calculated: 3.58
Cleavage perfect after {001}, good after {111}
colour colorless, gray-white, yellow to brownish-yellow; green to black due to inclusions
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.735 to 1.745

Periclase , chemically also known as magnesium oxide and colloquially as magnesia , is a rarely occurring mineral from the mineral class of "oxides and hydroxides" with the chemical composition MgO.

Periclase crystallizes in the cubic crystal system and develops small octahedral , more rarely also cuboctahedral or dodecahedral crystals , but also occurs in the form of granular to moderately coarse mineral aggregates . In its pure form, periclase is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also be translucent gray-white and, due to foreign admixtures, take on a yellow to brownish-yellow and, due to inclusions, green to black.

Etymology and history

The mineral was first discovered in 1841 by Arcangelo Scacchi on Monte Somma near Mount Vesuvius in Italy. It got its name based on its perfectly cubic cleavage after the Greek περί perí for "around", "around" or "all around" and klas for "break".

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the periclase belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio metal: oxygen = 1: 1 and 2: 1 (M 2 O, MO) ", where he named the" Periclas Group "with the system no. IV / A.04 and the other members bunsenite , calcium oxide , manganosite , monteponite , murdochite and wüstite .

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 periclase in the department of "Oxides with the molar ratio of metal: oxygen = 2: 1 and 1: 1". However, this is further subdivided according to the exact molar ratio and the relative size of the cations involved , so that the mineral is classified according to its composition in the subsection “Cation: Anion (M: O) = 1: 1 (and up to 1: 1.25); with only small to medium-sized cations ”is to be found, where it is also named after the“ periclase group ”with the system no. 4.AB.25 and the other members bunsenite, calcium oxide, ferropericlase, manganosite, monteponite and wüstite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the periclase to the class of "oxides and hydroxides" and there into the department of "oxides". Here, too, it is named in the " Periclas Group (Isometric, Fm3m) " with the system no. 04.02.01 to be found within the subsection “Simple oxides with a cation charge of 2+ (AO)”.

Crystal structure

Crystal structure of periclase

Periclase crystallizes in the cubic crystal system with the space group Fm 3 m (space group no. 225) with the lattice parameter a = 4.21  Å and four formula units per unit cell (sodium chloride structure). This structure remains stable up to pressures of at least 360 GPa. Template: room group / 225

properties

Powdered, periclase is soluble in water, producing magnesium hydroxide in an alkaline reaction .

Modifications and varieties

Periclase, variety Ferroperiklas from the San Vito quarry, Ercolano , Monte Somma, Naples, Italy (size 8.2 cm × 6.4 cm × 2.4 cm)

With ferropericlase , (Mg, Fe) O, an iron-containing variety of the periclase is known. Artificial periclase is also known as lavernite .

Education and Locations

Green nickel-containing periclase with black srebrodolskite from Ronneburg, Thuringia (image width 1.5 mm)

Periclase is formed by metamorphosis at high temperatures from magnesium-containing dolomite and limestone . It is associated depending on locality with forsterite and magnesite , brucite , Hydromagnesit and ellestadite or Fluorellestadit , lime , Magnesioferrit , hematite , Srebrodolskit and anhydrite .

In addition to the type locality, Periklas was found in Predazzo in Italy , Carlingford in Ireland , Broadford and Camas Mòr in Scotland , León in Spain , the Mayener Bellerberg in the Eifel ( Germany ), Nordmark and Långban in Sweden , Kopeisk in Russia , Crestmore , Tompstone and Gabbs in the United States , Oka in Canada, and Cowell in Australia .

With a volume fraction of around 20%, ferropericlase is the second most important mineral phase of the lower earth mantle after silicate Mg-Fe- perovskite (Mg, Fe) SiO 3 and there the main storage for iron; at the 660 km discontinuity the reaction γ- (Mg, Fe) 2 [SiO 4 ] ↔ (Mg, Fe) [SiO 3 ] + (Mg, Fe) O takes place, through the γ-olivine and a mixture of Perovskite and ferropericlase are converted into one another. In the literature, this mineral phase of the lower earth mantle is often referred to as magnesiowustite.

use

In the technical use of periclase or magnesia , a distinction is made between sintered magnesia and fused magnesia, whereby sintered magnesia is usually first calcined in a two-stage process at around 1100 ° C in a shaft furnace and then sintered in a rotary kiln. Magnesia that has already been completely deacidified can then be melted in an electric arc furnace. Periclase is pressed pure or in combination with other refractory raw materials into stones and, depending on its bond, fired (ceramic bond) or tempered (carbon bond). In connection with carbon ( soot and graphite ) magnesia-carbon products are produced, which are of great importance in steel production. They are highly temperature-resistant and show good chemical resistance to molten iron alloys and basic slags and are now state-of-the-art in converters and steel pans alongside Doloma carbon compounds.

In addition, pure magnesia bricks have good heat storage properties , so that they are used as storage cores in night storage heaters and electric fireplaces , among other things .

If magnesite is burned at lower temperatures of around 800 ° C, part of the carbon dioxide (CO 2 ) is retained. The resulting " caustic magnesia" remains reactive and, mixed with fillers, is processed into "Sorel cement" and used to manufacture refractory building materials and insulating compounds.

Because of its simple crystal structure, the physical properties of periclase have been studied very intensively, making it a popular test mineral e.g. B. is in the development of new techniques in experimental high pressure physics. There it is often used as a reference mineral for determining pressure.

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c R. Stewart McWilliams, Dylan K. Spaulding, Jon H. Eggert, Peter M. Celliers, Damien G. Hicks, Raymond F. Smith, Gilbert W. Collins, Raymond Jeanloz: Phase transformations and metallization of magnesium oxide at high pressure and temperature . In: Science . tape 338 , December 7, 2012, p. 1330-1333 , doi : 10.1126 / science.1229450 .
  2. ↑ a b c periclase . 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; 61  kB ; accessed on April 7, 2017]).
  3. ↑ 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. 289 .
  4. ↑ Mindat - Ferropericlase (English)
  5. ↑ Mindat - Lavernite (English)
  6. ↑ List of localities for periclase in the Mineralienatlas and Mindat
  7. ↑ Electric fireplaces as day or night electricity heating
  8. ↑ Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th fully revised and updated edition. Springer Verlag, Berlin et al. 2005, ISBN 3-540-23812-3 , pp. 64 .