Eucrite, cumulate
Purchased September 2002
coordinates not recorded
A small fusion-crusted 16.1 g stone was purchased in Agadir, Morocco by a Moroccan dealer, and subsequently sold to an American dealer. Analysis and classification was completed at the University of Washington in Seattle (S. Kuehner and A. Irving), and NWA 1828 was determined to be a cumulate eucrite. The meteorite has experienced a significant degree of shock as evidenced by the extensive fracturing, recrystallization, and melt veins. NWA 1828 consists of finely dispersed grains of anorthite and pigeonite, along with minor troilite, chromite, ilmenite, and silica.
Cumulate eucrites exist in a wide compositional range, and were formed as a result of fractional crystallization and gravitational settling within an evolved magma which had a composition similar to that of Nuevo Laredo. The resulting cumulate, composed of pyroxene and plagioclase in equilibrium with a trapped eucritic melt component, remained as a chemically closed system within a magma chamber. The incompatible element abundances present in cumulate eucrites were contributed by the trapped melt component; this LREE-enrichment indicates that the parental melts of cumulate eucrites were the same as or similar to those of noncumulate eucrites. Cooling probably occurred at depths of 3–8 km, consistent with intrusion into crustal material. The specimen of NWA 1828 pictured above is a 1.5 g partial end section.
