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In meteoritics, a meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially mineralogical, petrological, chemical, and isotopic properties.
A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primitive asteroids. Some such bodies that are captured in the planet's gravity well become the most common type of meteorite by arriving on a trajectory toward the planet's surface. Estimates for their contribution to the total meteorite population vary between 85.7% and 86.2%.
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies. As a result, achondrites have distinct textures and mineralogies indicative of igneous processes.
The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively. The composition of the Chelyabinsk meteorite is that of a LL chondrite meteorite. The material makeup of Itokawa, the asteroid visited by the Hayabusa spacecraft which landed on it and brought particles back to Earth also proved to be type LL chondrite.
The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After it broke up in the atmosphere, an extensive search for pieces was conducted and over 2 tonnes were recovered. The availability of large quantities of samples of the scientifically important chondrite class has enabled numerous investigations by many scientists; it is often described as "the best-studied meteorite in history." The Allende meteorite has abundant, large calcium–aluminum-rich inclusions (CAI), which are among the oldest objects formed in the Solar System.
Enstatite chondrites are a rare form of meteorite, rich in the mineral enstatite. Only about 200 E-Type chondrites are currently known, comprising about 2% of the chondrites that fall on Earth. There are two main subtypes: EH and EL, classified based on their iron content.
CI chondrites, also called C1 chondrites or Ivuna-type carbonaceous chondrites, are a group of rare carbonaceous chondrite, a type of stony meteorite. They are named after the Ivuna meteorite, the type specimen. CI chondrites have been recovered in France, Canada, India, and Tanzania. Their overall chemical composition closely resembles the elemental composition of the Sun, more so than any other type of meteorite.
Primitive achondrites are a subdivision of meteorites. They are classified on the same rank and lying between chondrites and achondrites. They are called primitive because they are achondrites that have retained much of their original chondritic properties. Very characteristic are relic chondrules and chemical compositions close to the composition of chondrites. These observations are explained as melt residues, partial melting, or extensive recrystallization.
Lodranites are a small group of primitive achondrite meteorites that consists of meteoric iron and silicate minerals. Olivine and pyroxene make up most of the silicate minerals. Like all primitive achondrites lodranites share similarities with chondrites and achondrites.
IAB meteorites are a group of iron meteorites according to their overall composition and a group of primitive achondrites because of silicate inclusions that show a strong affinity to winonaites and chondrites.
IIICD meteorites are a group of primitive achondrites. They are classified in a clan together with the IAB meteorites and the winonaites.
The Zakłodzie meteorite is a stony-iron meteorite found in Poland in 1998. Its mass is 8.68 kilograms (19.1 lb). It is composed predominantly from enstatite and meteoric iron. Currently classified as an ungrouped enstatite achondrite its classification is still an ongoing scientific debate.
The Itqiy meteorite is an enstatite-rich stony-iron meteorite. It is classified as an enstatite chondrite of the EH group that was nearly melted and is therefore very unusual for that group. Other classifications have been proposed and are an ongoing scientific debate.
The Winona meteorite is a primitive achondrite meteorite. It is the type specimen and by far the largest meteorite of the winonaite group.
Nonmagmatic meteorite is a deprecated term formerly used in meteoritics to describe iron meteorites that were originally thought to have not formed by igneous processes, to differentiate them from the magmatic meteorites, produced by the crystallization of a metal melt. The concept behind this was developed in the 1970s, but it was quickly realized that igneous processes actually play a vital role in the formation of the so-called "nonmagmatic" meteorites. Today, the terms are still sometimes used, but usage is discouraged because of the ambiguous meanings of the terms magmatic and nonmagmatic. The meteorites that were described to be nonmagmatic are now understood to be the product of partial melting and impact events and are grouped with the primitive achondrites and the achondrites.
This is a glossary of terms used in meteoritics, the science of meteorites.
Northwest Africa 7034 is a Martian meteorite believed to be the second oldest yet discovered. It is estimated to be two billion years old and contains the most water of any Martian meteorite found on Earth. Although it is from Mars it does not fit into any of the three SNC meteorite categories, and forms a new Martian meteorite group named "Martian ". Nicknamed "Black Beauty", it was purchased in Morocco and a slice of it was donated to the University of New Mexico by its American owner. The image of the original NWA 7034 was photographed in 2012 by Carl Agee, University of New Mexico.
Mason Gully is an ordinary chondrite of subclass H5, and is the second meteorite to be recovered using the Desert Fireball Network (DFN) camera observatory. One stone weighing 24.5g was observed to fall by the Desert Fireball Network observatory in Western Australia on 13 April 2010 at 10h36m10s UTC. It was recovered by the DFN on 3 November 2010 by Dr. R. Merle and the Fireball network recovery team, and was found 150m from its predicted fall location based upon the observed trajectory and calculated mass.
CM chondrites are a group of chondritic meteorites which resemble their type specimen, the Mighei meteorite. The CM is the most commonly recovered group of the 'carbonaceous chondrite' class of meteorites, though all are rarer in collections than ordinary chondrites.
The Jbilet Winselwan meteorite is a CM-type carbonaceous chondrite found in Western Sahara in 2013.
References
- 1 2 3 4 5 M. K. Weisberg; T. J. McCoy; A. N. Krot (2006). "Systematics and Evaluation of Meteorite Classification" (PDF). In D.S. Lauretta; H.Y. McSween Jr. (eds.). Meteorites and the early solar system II. foreword by Richard P. Binzel. Tucson: University of Arizona Press. pp. 19–52. ISBN 978-0816525621 . Retrieved 14 October 2013.
- ↑ "PAC Group – Primitive Achondrites". Meteorite.fr. Retrieved 10 December 2012.
- ↑ "Winona". meteorites.com.au. Retrieved 5 December 2012.
- ↑ M. M. Grady Catalogue of Meteorites (5th ed.) Cambridge UP, 2000, p. 528.
- ↑ A. L. Christenson "J. W. Simmons' account of the discovery of the Winona meteorite."Meteorite 10(3):14–16, 2004.
- ↑ "Meteoritical Bulletin Database". Meteoritical Society. Retrieved 18 April 2021.
- 1 2 3 4 Floss, Christine; CROZAZ, Ghislaine; JOLLIFF, Brad; BENEDIX, Gretchen; COLTON, Shannon (1 April 2008). "Evolution of the winonaite parent body: Clues from silicate mineral trace element distributions". Meteoritics & Planetary Science. 43 (4): 657–674. Bibcode:2008M&PS...43..657F. doi: 10.1111/j.1945-5100.2008.tb00676.x .
- 1 2 Benedix, G.K.; McCoy, T.J.; Keil, K.; Bogard, D.D.; Garrison, D.H. (30 June 1998). "A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism". Geochimica et Cosmochimica Acta. 62 (14): 2535–2553. Bibcode:1998GeCoA..62.2535B. doi:10.1016/S0016-7037(98)00166-5.
- ↑ Floss, Christine; Bradley L. Jolliff; Gretchen K. Benedix; Frank J. Stadermann; Jay Reid (2007). "Hammadah al Hamra 193: The first amphibole-bearing winonaite". American Mineralogist. 92 (4): 460–467. Bibcode:2007AmMin..92..460F. doi:10.2138/am.2007.2253 . Retrieved 6 December 2012.