![ALH84001 meteorite Smithsonian](https://upload.wikimedia.org/wikipedia/commons/3/35/ALH84001_meteorite_Smithsonian.jpg)
Orthopyroxenite is an
ultramafic
Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
and ultrabasic rock that is almost exclusively made from the mineral
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) ...
, the
orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...
version of
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 a type of
pyroxenite
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websteri ...
. It can have up to a few percent of
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 ...
and
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) ...
.
![Peridotite Olivine-Orthopyroxene-Clinopyroxene Orthopyroxenite highlighted](https://upload.wikimedia.org/wikipedia/commons/7/79/Peridotite_Olivine-Orthopyroxene-Clinopyroxene_Orthopyroxenite_highlighted.svg)
Orthopyroxenites can also occur on other planets.
ALH 84001 is a
Martian meteorite
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 ...
that can be classified as an orthopyroxenite. It is the only
meteorite
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
found with that composition and the only member of the
Martian orthopyroxenite group of meteorites.
References
Ultramafic rocks
Meteorites
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