The Brachina meteorite is the type specimen of the

brachinite Brachinites are a group of meteorites that are classified either as primitive achondrites or as asteroidal achondrites. Like all primitive achondrites, they have similarities with chondrites and achondrites. Brachinites contain 74 to 98% (volume) ...

s class of the

asteroidal achondrite An achondrite is a stony meteorite that does not contain chondrules. 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 recrystalliz ...

Naming and discovery

The meteorite is named after Brachina in

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

. Two fragments (total 200 g) were found by B.M. Eves at on 26 May 1974.

Description

The mineral composition of the Brachina meteorite is

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

(80%),

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...

(10%),

Clinopyroxene 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) ...

(5.5%), iron-sulfide (3%),

chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can s ...

(0.5%),

chlorapatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common end ...

(0.5%) and

pentlandite Pentlandite is an iron–nickel sulfide with the chemical formula . Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of wei ...

(0.3%) and traces of

meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal and early-universe protoplanetary-disk remnant found in meteorites and made from the elements iron and nickel, mainly in the form of the mineral phases kamacite and taenite. Meteoric iro ...

. Melt inclusions consist of glass with

orthopyroxene 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

anorthoclase The mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi3O8 and ...

. The chemical and mineralogical composition is similar to the

Chassigny meteorite Chassigny is a Martian meteorite which fell on October 3, 1815, at approximately 8:00 am, in Chassigny, north-eastern France.Pistollet (1816) The circumstances of the Chassigny meteorite shower. Ann. Chim. Phys. (Paris) v. 1, pg 45-48. Chassigny i ...

, but the trace elements are fundamentally different.

Parent body

Melt inclusions indicate that there were melting processes active on the

parent body.

Classification

The meteorite was classified as a

chassignite A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...

in 1978, but in 1983 trace element analysis showed that the Brachina meteorite was fundamentally different from Chassigny. It was therefore proposed that the meteorite should be the type specimen of a new meteorite class, the

s. This classification has remained valid since then.

References

{{Meteorites by name Achondrite meteorites Meteorites found in Australia Far North (South Australia)

Naming and discovery

Description

Parent body

Classification

See also

References