Amoeboid Olivine Aggregate

AOA in NWA 3118 using partially crossed-polarized light to see through the glassy melt. FOV=1.9mm. Image Credit: John Kashuba

Millimeter sized, fine-grained inclusions present to a few volume-percent in most carbonaceous chondrites. They can be round but can also be irregularly shaped like an amoeba (thus the name amoeboid). They are forsterite (Mg-rich olivine) and Ca-Al-Ti mineral aggregates. The most characteristic texture of AOAs is an anorthite core (sometimes associated with spinel and augite) rimmed by Al-diopside which overgrows olivine. AOAs were first described in the heavily altered Allende CV3 meteorite.

To see more images and get a more in-depth definition, please refer to the Nov 1, 2015 article in Meteorite Times by John Kashuba.

Some or all content above used with permission from J. H. Wittke.