Acapulcoite (Primitive)

Acapulcoite (Primitive)

Primitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated rocks with mineral compositions between those of E and H chondrites. Their oxygen isotope values set them apart from all other known chondrite groups. Some acapulcoites contain relict chondrules. NWA 725 from Tissemoumine, Morocco, has abundant distinct chondrules, confirming that acapulcoites are very primitive and are better termed metachondrites.

Acapulcoites and lodranites are thought to come from the same parent body, with lodranites showing evidence of slightly more melting of a chondritic source. However, the simple bimodal classification into acapulcoites and lodranites based on petrographic criteria is inadequate to fully describe the variability observed. These meteorites result from variable degrees of partial melting with and without accompanying melt migration. In some instances, their compositions have been changed by secondary processes on the parent body, such as metasomatism (Floss, 2000, MAPS 35:1073).

Content above used with permission from J. H. Wittke.

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