Angrites are a rare group of achondrites consisting mostly of Al-Ti bearing diopside, hedenbergite, olivine,

anorthite Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is Ca Al2 Si2O8. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon. Mineralo ...

and troilite with minor traces of phosphate and metals. The group is named for the

Angra dos Reis meteorite The Angra dos Reis meteorite is the type specimen of the angrite group. It was observed when it fell to earth in 1869. Discovery and naming The meteorite is named after Angra dos Reis, a municipality of Rio de Janeiro (state), Rio de Janeiro, Bra ...

. They are the oldest

igneous rocks Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

, with

crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...

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 the plutonic angrites cooled slower, deeper in the crust. The APB is thought to have been a similar size to the asteroid

4 Vesta Vesta (minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the ...

Origin

Angrite meteorites are distinct from other meteoritic groups based on their oxygen isotopic compositions. Based on their Mn-Fe ratios in

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

and other isotopic compositions, the source of angrites is constrained to the inner Solar System. However, recent studies have suggested that the APB experienced mixing of multiple sources during its history. By comparing the reflectance spectra of the angrites to that of several

main belt asteroids The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

, two potential parent bodies have been identified:

289 Nenetta Nenetta (minor planet designation: 289 Nenetta) is a typical A-type asteroid. It was discovered by Auguste Charlois on 10 March 1890 in Nice, France. The spectrum of 289 Nenetta reveals the strong presence of the mineral Olivine The mineral o ...

and 3819 Robinson. Other scientists have suggested that angrites could represent

ejecta Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma ...

from

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

, however later work has cast significant doubt upon these claims. Based on the lack of an asteroid matching the spectra of angrite meteorites it is thought that the APB was catastrophically disrupted and subsequently destroyed.

Notable meteorites

There are currently over 30 meteorites classified as angrites. The type specimen, the

, was an observed fall in 1869 and weighed . 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. NWA 10463 has been suggested to represent an intermediate stage between the quenched and plutonic angrite meteorites. NWA 8535 has been suggested to represent a Dunite. Asuka-12209; Asuka-88371 and NWA 12320 demonstrate an oxygen isotopic disequilibrium indicative of planetary mixing.

External links

D'Orbigny Angrite
- Meteorites Australia
Angrite Micro Visions
- Thin section pictures of angrites.

References

{{Meteorites Asteroidal achondrites

Origin

Notable meteorites

See also

External links

References