Sayh al Uhaymir 008 is one of the several pairings with SaU 005. These pairings have a total weigh of about 25 pounds. It is a Martian basaltic shergottite of a type sometimes called olivine-phyric.
It is composed of olivine megacrysts in a finer grained groundmass of pigeonite and plagioclase. In these cross-polarized light (XPL) photos the large olivine crystals are brightly colored. The pigeonite, a pyroxene, shows bands of color representing shock induced twinning. Here, the plagioclase, a feldspar, has been shocked to the glass-like form called maskelynite and appears black in XPL. Note that opaque minerals and voids also appear black.
Other shock features are melt pockets and attendant vacuoles. Often melt cools very fast to a glass as obsidian does in some volcanic situations. In one pocket in this thin section the melt had time to crystallize into fine, fernlike forms.
