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
A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...
and
achondrites
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 recrystalli ...
. Brachinites contain 74 to 98% (volume)
olivine
The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
.
Naming and history
Brachinites are named after the
Brachina meteorite, the type specimen of this group, which in turn is named after
Brachina,
South Australia
South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...
.
Description
Brachinites consist almost entirely of
olivine
The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
(74 to 98% by volume). Other minerals include
plagioclase
Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...
(6.7 to 12.9%), iron sulfides (1.8 to 4.0%),
clinopyroxene
The pyroxenes (commonly abbreviated 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 ions of calcium (Ca), sodium (Na), iron (Fe ...
(1.5 to 8.2%) and
orthopyroxene (0 to 2.4%). Trace minerals include phosphates and
meteoritic iron. The only deviation from
chondrites
A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...
is the very high olivine/orthopyroxene ratio.
Specimens
As of 2022, there were 56 meteorites classified as brachinites.
A notable example is the type specimen, the
Brachina meteorite.
See also
*
Glossary of meteoritics
This is a glossary of terms used in meteoritics, the science of meteorites.
#
* 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites.
* 4 Vesta – second-largest asteroid in the asteroid bel ...
References
{{meteorites
Asteroidal achondrites