Achondrite

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Achondrite
— Type —
Cumberland Falls meteorite.jpg
Cumberland Falls, achondrite (aubrite)
Compositional type Stony
MillbillillieMeteorite.jpg
An eucrite achondrite from the Millbillillie meteorite shower.

An achondrite[1] is a stony meteorite that does not contain chondrules.[2][3] 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.[4][5] As a result, achondrites have distinct textures and mineralogies indicative of igneous processes.[6]

Achondrites account for about 8% of meteorites overall, and the majority (about two thirds) of them are HED meteorites, possibly originating from the crust of asteroid 4 Vesta. Other types include Martian, Lunar, and several types thought to originate from as-yet unidentified asteroids. These groups have been determined on the basis of e.g. the Fe/Mn chemical ratio and the 17O/18O oxygen isotope ratios, thought to be characteristic "fingerprints" for each parent body.[7]

Classification[edit]

Achondrites are classified into the following groups:[8]

Primitive achondrites[edit]

Primitive achondrites, also called PAC group, are called in this way because their chemical composition is primitive in the sense that it is similar to the composition of chondrites, but their texture is igneous, indicative of melting processes. To this group belong:[8]

Asteroidal achondrites[edit]

Asteroidal achondrites, also called evolved achondrites, are called in this way because have been differentiated on a parent body. This means that their mineralogical and chemical composition was changed by melting and crytallization processes. They are divided several groups:[8]

Lunar meteorites[edit]

Lunar meteorites are meteorites that originated from the Moon.

Martian meteorite[edit]

Martian meteorites[10] are meteorites that originated from Mars. The are divided into three main groups, with two exceptions (see last two entries):

See also[edit]

References[edit]

  1. ^ Etymology: from the prefix a- (privative a) and the word chondrite.
  2. ^ Recommended classifications: Eucrite-pmict
  3. ^ Achondrite, Encyclopedia Britannica
  4. ^ Sahijpal, S.; Soni, P.; Gagan, G. (2007). "Numerical simulations of the differentiation of accreting planetesimals with 26Al and 60Fe as the heat sources". Meteoritics & Planetary Science 42 (9): 1529–1548. Bibcode:2007M&PS...42.1529S. doi:10.1111/j.1945-5100.2007.tb00589.x. 
  5. ^ Gupta, G.; Sahijpal, S. (2010). "Differentiation of Vesta and the parent bodies of other achondrites". J. Geophys. Res. (Planets) 115. Bibcode:2010JGRE..11508001G. doi:10.1029/2009JE003525. 
  6. ^ Mason, B. (1962). Meteorites. New York: John Wiley. 
  7. ^ Mittlefehldt, David W.; McCoy, Timothy J.; Goodrich, Cyrena Anne; Kracher, Alfred (1998). "Non-chondritic Meteorites from Asteroidal Bodies". Reviews in Mineralogy and Geochemistry 36 (1): 4.1–4.195. 
  8. ^ a b c O. Richard Norton. The Cambridge encyclopedia of meteorites. UK, Cambridge University Press, 2002. ISBN 0-521-62143-7.
  9. ^ Drake, M. J. (2001). "The eucrite/Vesta story". Meteoritics and Planetary Science 36 (4): 501–513. Bibcode:2001M&PS...36..501D. doi:10.1111/j.1945-5100.2001.tb01892.x. 
  10. ^ Treiman, A. H. (2000). "The SNC meteorites are from Mars". Planetary and Space Science 48 (12–14): 1213–1230. Bibcode:2000P&SS...48.1213T. doi:10.1016/S0032-0633(00)00105-7. 

External links[edit]