Poikilitic shergottite
A poikilitic shergottite is a Martian rock in which large pyroxene crystals enclose many smaller olivine grains.
A poikilitic shergottite has a texture in which large crystals of pyroxene, sometimes centimetres across, enclose numerous small olivine and chromite grains. 'Poikilitic' comes from a Greek word meaning spotted or mottled. Between these large crystals are non-poikilitic areas of olivine, pyroxene and maskelynite.
This type was formerly called lherzolitic shergottite, after a mantle rock on Earth, but the term poikilitic is now preferred because the rocks are not true mantle samples. They are cumulate-like rocks that crystallised slowly at some depth in the Martian crust. Examples include ALH A77005 and Lewis Cliff 88516 from Antarctica, and several finds from northwest Africa.
Poikilitic shergottites are among the coarsest-grained Martian meteorites. Their textures show that large pyroxene crystals grew around earlier olivine, recording the order of crystallisation in a slowly cooling Martian magma chamber.
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