Acapulcoite
Acapulcoites are fine-grained primitive achondrites that experienced only small degrees of partial melting.
The acapulcoites are named after Acapulco, a stone of about 1.9 kilograms that fell near Acapulco, Mexico, on 11 August 1976. They are equigranular rocks of orthopyroxene, olivine, iron-nickel metal, troilite and plagioclase, with grain sizes typically a few hundred micrometres or less. Some contain relict chondrules, a strong hint that their precursor was a chondrite. Minerals are relatively reduced, intermediate between H and enstatite chondrites in their iron content.
Acapulcoites underwent only low degrees of partial melting, reaching the iron–nickel–sulfide eutectic and in many cases starting to produce small amounts of silicate melt, which moved only short distances. They share oxygen isotopes and cosmic-ray exposure ages with the coarser lodranites, so both are thought to come from one parent body, with acapulcoites from shallower, less heated layers. Precise radiometric ages show they formed and cooled within the first few million years of Solar System history.
Most known acapulcoites are finds from Antarctica and hot deserts. Recognition depends on their fine, recrystallised texture, mineral compositions, chondritic-like bulk chemistry, and oxygen isotopes matching the acapulcoite–lodranite clan.
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