Northwest Africa 12565 (NWA 12565)

Morocco

Purchased: 2012

Classification: Carbonaceous chondrite (CV3)

History: Purchased by David DGregory in Tucson, 2012. Catalogued at ROM as LM57457

Physical characteristics: Physical Characteristics: Specimen is a 143.7 g light-brown, sub-spherical stone with a thin, glassy fusion crust. On the exposed cut surface, multiple oxidized fractures visibly cross-cut the varying proportions of chondritic material. Few of the larger, mm-sized chondrules have oxidation rims.

Petrography: Specimen contains varying proportions of mm-sized chondrules with igneous rims (avg: 0.95±0.33 mm, n=70), calcium- and aluminum-rich inclusions (CAIs) and sub-mm mineral fragments set in an opaque and crystalline matrix. Chondrules are primarily magnesian, porphyritic, and contain forsterite and low-Ca pyroxene phenocrysts surrounded by feldspathic glass and relatively low amounts of Fe-Ni metal. Modal percentage of components is ~30% for chondrules, ~20% for CAIs, 4.5% for Fe-oxides and remaining is feldspathic glass. Specimen is weakly shocked (S3), determined by presence of intersecting sets of irregular fractures in olivine crystals, undulatory extinction in olivines and pyroxenes, and melt pockets. Minor oxide rims present around metal in chondrules, and small, irregular oxide veins occur throughout the chondritic components, indicative of minor weathering.

Geochemistry: Forsterite in chondrules has a mean composition of Fa_3.8±3.8, n=53. Specimen exhibits chemistry from generally Mg-rich cores progressing to more Fe-rich rims. Individual forsterite grains also exhibit chemical heterogeneity, characterized by Mg-rich forsterite cores with progressive Fe enrichment near grain boundaries. Pyroxene in chondrules has a composition of Fs_3.4±18.5Wo_15.8±5.7, n=73. Pyroxene in chondrules and individual phenocrysts exhibit chemical heterogeneity from relatively Mg-rich cores progressing to Fe enrichment at the boundaries. Metal droplets have taenite Ni content 47.5±2.7). Secondary grains are composed primarily of olivine and pyroxene, and trace amounts of plagioclase. Oxygen isotopes (K. Ziegler, UNM): acid-treated powders gave an average of δ¹⁷O=-2.240 ‰; δ¹⁸O=2.697 ‰; Δ¹⁷O=-3.664 ‰ (N=3).

Classification: Carbonaceous chondrite (CV3). O isotopes plot on a single trend near the CCAM trend line and fall within the CV group. Petrologic type 3 determined by chemical heterogeneity exhibited in olivine and pyroxene-group minerals in chondrules, which have greater than 5% mean deviations, expected for a highly unequilibrated chondrite. Additional characteristics indicative of a type 3 chondrite includes high proportions of monoclinic low-Ca pyroxene phenocrysts in the chondrules, absence of optically resolvable feldspar grains, and taenite Ni content. Chondrules are sharply defined, and the matrix is opaque.

Specimens: The ROM holds the main mass of the sample which weighs 143.17 g. The remaining specimen is composed of two fragments, thin section and a thin section billet.