astro.wikisort.org - Meteorite

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]

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

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

Achondrites are classified into the following groups:[8]

• Primitive achondrites
• Asteroidal achondrites
• Lunar meteorites
• Martian meteorites

Primitive achondrites

Primitive achondrites, also called PAC group, are so-called 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]

• Acapulcoites (after the meteorite Acapulco, Mexico)
• Lodranites (after the meteorite Lodran)
• Winonaites (after the meteorite Winona)
• Ureilites (after the meteorite Novy Ureii, Russia)
• Brachinites (after the meteorite Brachina)

Asteroidal achondrites

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

• HED meteorites (Vesta). They may have originated on the asteroid 4 Vesta, because their reflection spectra are very similar.[9] They are named after the initial letters of the three subgroups:
  • Howardites
  • Eucrites
  • Diogenites
• Angrites
• Aubrites

Lunar meteorites

Lunar meteorites are meteorites that originated from the Moon.

Martian meteorite

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

• Shergottites
• Nakhlites
• Chassignites
• OPX martian meteorites (ALH 84001)
• Regolith/Soil samples (NWA 7034 and pairings)

See also

• Glossary of meteoritics

References

External links

• Achondrite Images from Meteorites Australia

На других языках

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[de] Achondrit

Achondrite (griech. ά (a-), ‚ohne‘ und χόνδρος (chondros), ‚Korn‘) sind Steinmeteorite, die im Gegensatz zu den viel häufigeren Chondriten keine oder nur noch wenige Chondren enthalten. Anhand von Element- und Isotopenverhältnissen werden Achondrite in Gruppen eingeteilt. Unterschieden werden primitive Achondrite, die sich von Chondriten nur in der Textur unterscheiden und Reste von Chondren enthalten können, und differenzierte Steinmeteorite, die an Eisen und in Eisen löslichen Elementen verarmt sind. Sie wurden aus der Kruste oder dem Mantel größerer Mutterkörper herausgeschlagen, die sich bei ihrer Entstehung in einen Eisenkern und Mantel differenziert haben. Drei Gruppen, die zusammen etwa zwei Drittel der Achondrite ausmachen, stammen wahrscheinlich vom Asteroiden (4) Vesta, einige vom Mond und vom Mars, andere konnten bisher nicht zugeordnet werden.

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- [en] Achondrite

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[ru] Ахондрит

Ахондриты — каменные метеориты без округлых включений - хондр. По составу и структуре близки земным базальтам. Все ахондриты в той или иной степени претерпели плавление, которое и уничтожило хондры. Ахондриты являются довольно распространенным типом метеоритов. Они составляют около 8 % от всех найденных метеоритов.

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