Bridgmanite

from Wikipedia, the free encyclopedia
Bridgmanite
General and classification
other names

IMA 2014-017

chemical formula MgSiO 3
Mineral class
(and possibly department) 		Oxides and hydroxides
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pnma (No. 62)Template: room group / 62
Lattice parameters a  = 5.02  Å ; b  = 6.90 Å; c  = 4.81 Å
Physical Properties
Mohs hardness not defined
Density (g / cm 3 ) calculated: 4.107
Cleavage not defined
colour not defined
Line color not defined
transparency transparent
shine not defined

Bridgmanite is a mineral from the group of silicate perovskites . It crystallizes in the orthorhombic crystal system with the chemical composition Mg Si O 3 and, due to its perovskite structure, belongs to the oxides and thus to the mineral class of "oxides and hydroxides".

Bridgmanite is a very common mineral in the lower mantle . So far, however, it has only been found on the earth's surface in the form of microcrystalline grains as inclusions in a meteorite that fell in Australia .

Etymology and history

Bridgmanit was named after the physicist Percy Williams Bridgman, who was awarded the Nobel Prize in 1946 for his pioneering work in the field of experimental high pressure physics .

The crystalline structure of the mineral was determined for the first time in 1974 by investigating samples synthetically produced in high pressure presses. However, direct investigations on natural mineral samples have so far failed because the mineral only occurs in the earth from a depth of around 660 kilometers in the lower mantle .

It was not until a natural sample was discovered in a fragment of the Tenham meteorite , which fell in 1879 near Tenham Station in the Charters Towers Queensland region in Australia , and was investigated by researchers working with Oliver Tschauner from the University of Nevada and Chi Ma at the California Institute of Technology finally led to the official recognition of the mineral by the Commission on new Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA).

Fragments of the Tenham meteorite are kept in the Smithsonian Institution's National Museum of Natural History (Catalog No. USNM 7703).

classification

Bridgmanite was only recognized and published as an independent mineral by the IMA in 2014. An exact group assignment in the 9th edition of the Strunz'schen mineral systematics , the last update of which was carried out with the publication of the IMA list of mineral names in 2009, is therefore not yet known. Due to its close relationship with the minerals perovskite (system no. 4.CC.30) and akimotoite (since 2014 classified as oxides in the newly defined ilmenite group 4.CB.), Bridgmanite is probably also in one of the subdivisions within the department of " oxides with the molar ratio metal: oxygen = 2: 3, 3: 5 and comparable ".

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on the classic systematics of Karl Hugo Strunz in the 8th edition , the mineral was given the system and mineral number. VIII / F.02-36 . In the "lapis system" this corresponds to the class of "silicates and germanates" and there the department "chain and band silicates", where bridgmanite together with akimotoite, donpeacorite , enstatite , ferrosilite , nchwaningite and protoenstatite form the group of "orthopyroxenes" .

Crystal structure

Bridgmanite crystallizes orthorhombically in the space group Pnma (space group no. 62) with the lattice parameters a  = 5.02 ± 0.03  Å ; b  = 6.90 ± 0.03 Å and c  = 4.81 ± 0.02 Å and a cell volume of 167 ± 2 Å 3 . Template: room group / 62

Modifications and varieties

Pressure-temperature phase diagram for the compound MgSiO 3

The compound MgSiO 3 is polymorphic and still comes in addition to the orthorhombic crystallized Bridgmanit (perovskite structure) as trigonal crystallizing Akimotoit with ilmenite, tetragonal or cubic as majorite with garnet structure , as monoclinic clino-enstatite and orthorhombic as Orthoenstatit with Pyroxenstruktur before.

Education and Locations

Molar volume as a function of pressure for Bridgmanite at room temperature

Bridgmanite forms in the lower mantle of the earth, where it is formed at temperatures of approx. 1800 ° C and pressures of over 240,000  bar (24  GPa ). With a share of 38 percent of the total mass, the mineral is the most abundant on earth, but does not occur on the earth's surface due to its formation conditions.

The only find naturally formed bridgmanite outside the Earth's mantle is the Tenham meteorite discovered in Australia. The energy when the meteorite hit had created conditions comparable to those in the earth's mantle, through which the mineral was created. In the Tenham meteorite, bridgmanite occurred in paragenesis with akimotoite . In 2018, the mineral could also be detected in tiny diamonds.

literature

  • Oliver Tschauner, Chi Ma, John R. Beckett, Clemens Prescher, Vitali B. Prakapenka, George R. Rossman: Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite . In: Science . tape 346 , no. 6213 , November 28, 2014, p. 1100-1102 , doi : 10.1126 / science.1259369 .

Web links

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

Individual evidence

  1. ↑ a b c d e f g h Oliver Tschauner, Chi Ma, John R. Beckett, Clemens Prescher, Vitali B. Prakapenka, George R. Rossman: Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite . In: Science . tape 346 , no. 6213 , November 28, 2014, p. 1100-1102 , doi : 10.1126 / science.1259369 .
  2. ^ Joseph R. Smyth, Tamsin C. McCormick: Crystallographic Data For Minerals . In: Thomas J. Ahrens (Ed.): Mineral Physics and Crystallography: A Handbook of Physical Constants . AGU, Washington, DC 1995, p. 8 , doi : 10.1029 / RF002p0001 ( full access to PDF files in the web archive ( Memento from March 4, 2016 in the Internet Archive ) - MgSiO 3 -Perovskite, p. 8).
  3. ^ JoAnna Wendel: Mineral Named After Nobel Physicist . In: Eos. Transactions American Geophysical Union . tape 95 , no. 23 , 2014, p. 195 , doi : 10.1002 / 2014EO230005 .
  4. ↑ a b Earth's mantle. Spektrum Akademischer Verlag, accessed December 14, 2014 .
  5. ^ IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). Newsletter 21 . In: Mineralogical Magazine . tape  78 , no. 4 , August 2014, p. 797-804 ( cnmnc.main.jp [PDF; 96 kB ; accessed on March 29, 2018] IMA No. 2014-017 Bridgmanite p. 798).
  6. ↑ 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 (English, with the last official Strunz classification).
  7. ↑ Malcom E. Back: Fleischer's Glossary of Mineral Species . 11th edition. Mineralogical Record, Tucson, Arizona (AZ) 2014, p. 358 .
  8. ↑ 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 .
  9. ↑ Naotaka Tomioka and Masaaki Miyahara: High-pressure minerals in shocked meteorites . In: Meteoritics & Planetary Science . tape 52 , no. 9 , 2017, p. 2017–2039 ( researchgate.net [PDF; 107 kB ; accessed on February 3, 2018]).
  10. ↑ Minerals: The most common rock on earth finally has a name. Spectrum of Science , accessed November 28, 2014 .
  11. ↑ Evan M. Smith, Steven B. Shirey, Stephen H. Richardson, Fabrizio Nestola, Emma S. Bullock, Jianhua Wang & Wuyi Wang: Blue boron-bearing diamonds from Earth's lower mantle . In: Nature . tape 560 , no. 7716 , August 2018, ISSN  0028-0836 , p. 84-87 , doi : 10.1038 / s41586-018-0334-5 .