Choteau Pallasite Meteorite |
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This specimen weighs 86 grams. It measures 95 mm by 81 mm by 3.1 mm thick. All measurements taken at widest points. |
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Purchased in 2011 by Debbie Cilz at an estate sale in Choteau, Montana,
and presumed to have been found locally by the deceased owner. A
single dense, brownish mass weighing 8474 g. Interior slices exhibit
separated, angular clasts of olivine (~40 vol.%) within metal.
Composed predominantly of metal (kamacite with Ni-poor taenite) and large
angular grains of olivine with accessory iron sulfide (pyrrhotite),
schreibersite, merrillite, chromite and orthopyroxene. One large (4.5 mm)
grain of exsolved calcic pyroxene was found (now composed of augite with
orthopyroxene exsolution lamellae). Chromite and orthopyroxene occur in
symplectitic intergrowths, and there also are small patches composed of
chromite+iron sulfide+merrillite exhibiting triple grain junctions.
Classified as a Pallasite, ungrouped. The oxygen isotopic composition is
unlike those for any other pallasites, and falls on the broad trend for
acapulcoites and lodranites. |
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