Crotite

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Crotite
General and classification
other names

IMA 2010-038

chemical formula CaAl 2 O 4
Mineral class
(and possibly department) 		Oxides and hydroxides
Similar minerals Dmitryivanovite
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / n (No. 14, position 2)Template: room group / 14.2
Lattice parameters a  = 8.6996 (3)  Å ; b  = 8.0994 (3) Å; c  = 15.217 (1) Å
β  = 90.188 (6) °
Formula units Z  = 12
Physical Properties
Mohs hardness ≈ 6.5
Density (g / cm 3 ) calculated: 2.944
Cleavage good after {100} and {010}
Break ; Tenacity clamshell; brittle
colour colorless
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.608 (2)
n β  = 1.629 (2)
n γ  = 1.635 (2)
Optical character biaxial negative
Axis angle 2V = measured: 54.4 (5) °; calculated: 55.6 °
Pleochroism colorless to very pale gray

Crotite is an extremely seldom occurring mineral from the mineral class of "oxides and hydroxides" with the chemical composition CaAl 2 O 4 and thus, chemically speaking, a calcium - aluminum - oxide .

Crotite crystallizes in the monoclinic crystal system and has so far only been found in the form of microcrystalline, colorless and transparent inclusions in a meteorite .

Etymology and history

Krotit was first discovered in 2010 in a carbonaceous chondrite called NWA 1934 , which fell near the town of Rissani in the Moroccan province of Errachidia . The mineral was described by Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith and Devin L. Schrader, who named it after the geochemist Alexander N. Krot (* 1959) named. The mineral and its name were recognized by the International Mineralogical Association (IMA) that same year .

Three thin sections with the designations "UA2169TS1", "UA2169TS2" and "UA2169TS3" contain the type material of the mineral. Thin section UA2169TS1 is available under catalog no. USNM 7590 in the Smithsonian Institution in Washington, DC and the co-type material (with crotite fragments of the thin section UA2169TS2) is available under catalog no. 63275 in the Natural History Museum of Los Angeles County in South Los Angeles , USA.

classification

Krotit was only recognized by the IMA as an independent mineral in 2010. An exact group assignment in the 9th edition of Strunz's mineral system is therefore not yet known, as the system was last updated by the IMA in 2009.

However krotite is dimorphic with the known since 2006 Dmitryivanovit (CaAI 2 O 4 , IMA 2006-035 and crystallized) like this in monoclinic symmetry, albeit with slightly different lattice parameters. Dmitryivanovit was in the class of oxides with the molar ratio of metal: 4 and comparable and there in the subsection ": oxygen = 3 with only midsize cations classified" where he is the only member of the unnamed group 4.BB forms. Due to the close relationship, Krotit will therefore probably also be sorted there.

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, albeit outdated, classification form by Karl Hugo Strunz in the 8th edition , the mineral received the system and Mineral no. IV / B.09-07 . In the "lapis system" this corresponds to the class of "oxides and hydroxides" and there the section "oxides with the ratio metal: oxygen = 3: 4 (spinel type M 3 O 4 and related compounds)", where crotite together with dmitryivanovite and Grossit forms an independent but unnamed group.

Crystal structure

Crotite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a  = 8.6996 (3)  Å ; b  = 8.0994 (3) Å; c  = 15.217 (1) Å and β = 90.188 (6) ° and 12 formula units per unit cell . Template: room group / 14.2

Education and Locations

Crotite occurs at its first place of discovery , the Moroccan meteorite NWA 1934 , as the core of an egg-shaped calcium-aluminum-rich inclusion (CAI) of 2.75 mm × 4.5 mm in size, which is surrounded by olivine . In addition to crotite, the inclusion contains small amounts of perovskite , gehlenite , hercynite , hexamolybdenum and chloromayenite in fine veins and inclusions. The inclusion is surrounded by a rim of grossite , hibonite and spinel , gehlenite and an outer layer of aluminum-rich diopside .

The meteorite and the mineral crotite it contains were probably formed more than 4.5 billion years ago by condensation or crystallization from a melt in the young solar nebula that had condensed from the primeval cloud . This makes crotite one of the oldest known minerals in the solar system.

In addition to its type locality, the mineral has so far (as of 2019) only been discovered at one other location, namely in the rockefet magmatic complex in the Carmel Mountains in northern Israel.

See also

literature

  • Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith, Devin L. Schrader: Krotite, CaAl 2 O 4 , a new refractory mineral from the NWA 1934 meteorites . In: American Mineralogist . tape 96 , 2011, p. 709-715 ( caltech.edu [PDF; 4.8 MB ; accessed on January 14, 2018]).
  • Anne M. Hofmeister, Brigitte Wopenka, Andrew J. Locock: Spectroscopy and structure of hibonite, grossite, and CaAl 2 O 4 : Implications for astronomical environments . In: Geochimica et Cosmochimica Acta . tape 68 , 2004, p. 4485-4503 , doi : 10.1016 / j.gca.2004.03.011 .

Web links

Individual evidence

  1. ↑ a b c d e f g h Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith, Devin L. Schrader: Krotite, CaAl 2 O 4 , a new refractory mineral from the NWA 1934 meteorite . In: American Mineralogist . tape 96 , 2011, p. 709 ( its.caltech.edu [PDF; 5.0 MB ; accessed on September 27, 2019]).
  2. ↑ a b c d Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith, Devin L. Schrader: Krotite, CaAl 2 O 4 , a new refractory mineral from the NWA 1934 meteorite . In: American Mineralogist . tape 96 , 2011, p. 711 ( [1] [PDF; 5.0 MB ; accessed on September 27, 2019]).
  3. ↑ PA Williams, F. Hatert, M. Pasero, SJ Mills: IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). NEWSLETTER 5. New minerals and nomenclature modifications approved in 2010 . In: Mineralogical Magazine . tape 74 , no. 5 , October 2010, p. 899–902 ( cnmnc.main.jp [PDF; 66 kB ; accessed on September 27, 2019] Krotite IMA No. 2010-038 from p. 2).
  4. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed July 11, 2019 .
  5. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, p. 131 , accessed July 11, 2019 .
  6. ↑ 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. ↑ Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith, Devin L. Schrader: Krotite, CaAl 2 O 4 , a new refractory mineral from the NWA 1934 meteorite . In: American Mineralogist . tape 96 , 2011, p. 710 ( its.caltech.edu [PDF; 5.0 MB ; accessed on September 27, 2019]).
  8. ↑ Meteorite brought unknown mineral to earth. In: spiegel.de. Spiegel Online , May 9, 2011, accessed July 11, 2019 .
  9. ↑ Newly discovered meteorite mineral originated in primeval cloud. “Crotite” is one of the oldest minerals in the solar system. In: scinexx.de. scinexx das wissensmagazin, May 10, 2011, accessed on August 29, 2019 .
  10. ↑ Find location list for crotite in the Mineralienatlas and Mindat (accessed on July 11, 2019).