NORTHWEST AFRICA 12455


CR7 (CR8; Irving et al., 2019)
standby for nwa 12455 photo
Purchased Nov 2018
no coordinates recorded

A relatively fresh stone weighing 611 g was purchased by B. Hoefnagels from a meteorite dealer in Agadir, Morocco. The stone was analyzed at the University of Washington in Seattle (A. Irving and S. Kuehner) and Washington University in St. Louis (P. Carpenter), and it was determined that NWA 12455 is a completely recrystallized, texturally evolved CR7 chondrite.

Northwest Africa is composed of olivine, orthopyroxene, and plagioclase grains forming triple junctions, along with lesser FeNi-metal (kamacite and taenite), FeS (troilite and pentlandite), chromite, and minor terrestrial alteration products. No relict chondrules were observed in the studied sections. The O-isotopic composition for NWA 12455 was investigated at the University of New Mexico (K. Ziegler), and the values for six subsamples clearly plot along the CR trend line. Similarly, the Cr-isotopic composition was investigated at the University of California, Davis (M. Sanborn and Q. Yin), and the 54Cr value was determined to be the same within uncertainty as that for Renazzo.

A further metamorphic category in the textural continuum—type 8—has been proposed by Irving et al. (2019) to distinguish between those highly metamorphosed meteorites in which relict chondrules can still be discerned (e.g., NWA 12272 [LL7]) and those which exhibit a completely recrystallized texture (e.g., NWA 3133 [CV7]). The designation of type 8 was also suggested for other chondrite groups with members having similar completely recrystallized textures, including CK (e.g., NWA 8186 [Achon-ung]), CR (e.g., NWA 12455), and H (e.g., NWA 4226 [H7]), as well as certain meteorites within the acapulcoite and winonaite groups (see Irving et al., 2019 #6399). The specimen of NWA 12455 shown above is a 0.30 g partial slice. The top photo below shows a slice of this meteorite with a larger surface area, while the bottom image is a petrographic thin section micrograph showing the recrystallized structure of NWA 12455.

standby for nwa 12455 slice photo
click on image for a magnified view
Photo courtesy of Ben Hoefnagels

standby for nwa 12455 ts photo
click on image for a magnified view
Photo courtesy of Anthony Irving