ACAPULCOITE
Acapulcoites are rare achondrite meteorites (=
meteorites that lack rounded structures called chondrules). About 64
acapulcoites have been documented. They have a finely-crystalline texture
and are composed of a mix of mafic silicate minerals (olivine, pyroxenes,
plagioclase feldspar) and metallic iron-nickel.
The overall chemistry of acapulcoites is generally the
same overall chemistry seen in ordinary chondrites. This suggests that
acapulcoites are the result of metamorphic heating of chondrite material,
involving solid-state recrystallization but generally no significant loss or
gain of component elements. Such rocks have been called metachondrites
(metamorphosed chondrites).
The sample shown below is the NWA 2989 Meteorite,
found in northwestern Africa in 2005. It is reportedly paired with
several other acapulcoites discovered in the same general area (the list
includes at least the following: NWA 2656, NWA 2699, NWA 2714, NWA 2866, and
NWA 2871).
The specific parent body in the asteroid belt from
which acapulcoites are derived is unknown. What is known is that another
group of rare achondrite meteorites, the lodranites, come from the same
body.
Published age information on acapulcoites shows that
the parent body is 4.555 to 4.562 billion years old. Most acapulcoites
& lodranites have cosmic-ray exposure dates of 4 to 7 million years,
indicating when these rocks were ejected from the parent body.
Acapulcoite slice (above & below; 1.3 cm across at its widest) showing
microcrystalline texture and mixture of mafic silicate minerals &
iron-nickel metal. The Fe-Ni metal shows up black in the photo above
& bright silver in the photo below. Note the thin veins of metal
running through the rock. This is characteristic of acapulcoites.
Acapulcoite
(More info. on NWA
2989, which = NWA 2656)
Info. mostly synthesized from Hutchinson (2004 - Meteorites,
a Petrologic, Chemical and Isotopic Synthesis) and Touboul et al. (2007 - 38th
Lunar and Planetary Science Conference Abstracts # 2317). Some info.
from James Wittke & John Kashuba & David Weir.