| Angrite | |
|---|---|
| — Group — | |
 A slice of NWA 2999. Note the similarity to a terrestrialbasalt. | |
| Compositional type | Stony meteorite |
| Type | Achondrite |
| Subgroups | Quenched Plutonic |
| Parent body | Possibly289 Nenetta,3819 Robinson orMercury |
| Total known specimens | 30+ |
Angrites are a rare group ofachondrites consisting mostly of Al-Ti bearingdiopside,hedenbergite,olivine,anorthite andtroilite with minor traces ofphosphate and metals. The group is named for theAngra dos Reis meteorite. They are the oldestigneous rocks, withcrystallization ages of around 4.56 billion years. Angrites are subdivided into two main groups, the quenched and plutonic angrites. The quenched angrites cooled rapidly upon the surface of the angrite parent body (APB), whereas theplutonic angrites cooled slower, deeper in thecrust. The APB is thought to have been a similar size to the asteroid4 Vesta.
Angrite meteorites are distinct from other meteoritic groups based on theiroxygen isotopic compositions.[1] Based on their Mn-Fe ratios inpyroxene and other isotopic compositions, the source of angrites is constrained to the innerSolar System. However, recent studies have suggested that the APB experienced mixing of multiple sources during its history.[2]
By comparing thereflectancespectra of the angrites to that of severalmain belt asteroids, two potential parent bodies have been identified:289 Nenetta and3819 Robinson. Other scientists have suggested that angrites could representejecta fromMercury, however later work has cast significant doubt upon these claims.[3]
Based on the lack of an asteroid matching thespectra of angrite meteorites it is thought that the APB was catastrophically disrupted and subsequently destroyed.
There are currently over 30 meteorites classified as angrites. The type specimen, theAngra dos Reis meteorite, was an observed fall in 1869 and weighed 1.5 kilograms (3.3 lb). Most of it has been lost over time; the largest remaining piece, weighing 101 grams, is kept at the Museum of Natural History in Rio de Janeiro.[4]
NWA 10463 has been suggested to represent an intermediate stage between the quenched and plutonic angrite meteorites.[5]
NWA 8535 has been suggested to represent aDunite.[6]
Asuka-12209; Asuka-88371 and NWA 12320 demonstrate an oxygen isotopic disequilibrium indicative of planetary mixing.[2]