Achondrite

Template:Short description Template:Infobox meteorite subdivision An achondrite<ref>Etymology: from the prefix a- (privative a) and the word chondrite.</ref> is a stony meteorite that does not contain chondrules.<ref>Recommended classifications: Eucrite-pmict</ref><ref>Achondrite, Encyclopædia Britannica</ref> 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.<ref name="Sahijpal2007">Template:Cite journal</ref><ref name="Gupta2010">Template:Cite journal</ref> As a result, achondrites have distinct textures and mineralogies indicative of igneous processes.<ref>Template:Cite book</ref>

Achondrites account for about 8% of meteorites overall, and the majority (about <math>2/3</math>) of them belong to the HED clan, possibly originating from the crust of asteroid 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.<ref>Template:Cite journal</ref>

ClassificationEdit

Achondrites are classified into the following groups:<ref name=cambridgeencyclopedia>O. Richard Norton. The Cambridge encyclopedia of meteorites. UK, Cambridge University Press, 2002. Template:ISBN.</ref>

Primitive achondritesEdit

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:<ref name=cambridgeencyclopedia />

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 achondritesEdit

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 into several groups:<ref name=cambridgeencyclopedia />

HED meteorites (Vesta). They may have originated on the asteroid 4 Vesta, because their reflection spectra are very similar.<ref>Template:Cite journal</ref> They are named after the initial letters of the three subgroups:
Angrites
Aubrites

Lunar meteoritesEdit

Lunar meteorites are meteorites that originated from the Moon.

Martian meteoriteEdit

Martian meteorites<ref>Template:Cite journal</ref> are meteorites that originated from Mars. They are divided into three main groups, with two exceptions (see last two entries):