Northwest Africa 14762 (NWA 14762)

(Northwest Africa)

Purchased: October 2018

Classification: Ordinary chondrite (LL5)

History: The specimen was bought for the "MECSO Project - A window on the Solar System: a project for the spectroscopic characterization of bolids.

Physical characteristics: The specimen was acquired as an almost pristine (W0/1) meteorite with a nearly complete fresh fusion crust. Thanks to a proper conservation, it was still pristine six months later, when it was used for the MECSO Project. Then, during the following three years, it was temporary deposited at the Natural History Museum of UniFi. Here, due to the environmental conditions, the small fragment of the specimen and the external portion of the main mass weathered to W2-3 grade.

Petrography: Brecciated texture with light recrystallized matrix and highly fractured chondrules with still visible margins. It is present a large clast affected by darkening, no chondrules and olivines with evident undulatory extinction. Overally, whole chondrules are rare, being more often fragmented intermixed with olivine and pyroxenes crystals. Plagioclase grains in the matrix have small sizes (less than 50 um). Silicatic phases are fresh, rarely affected by staining. Opaques moderate to heavy weathered (sometimes totally replaced by) in Fe-oxy/hydroxides. Weathering grade observed in the thin section of a not properly conserved small fragment is W2/3. Shock stage between 2 and 3 (S2/3), since olivines display clear undulatory optical extinction, but apparently no planar fractures have been detected (although the highly fractured appearance could mask their presence).

Geochemistry: Olivine Fa_29.5-32.2 FeO/MnO=60.0 (N=44), low-Ca pyroxene Fs_25.9-27.2 Wo_2.0-2.4 FeO/MnO=38.3 (N=31), high-Ca pyroxene Fs_10.0-14.0, Wo_33.2-43.1 FeO/MnO=33.3 (N=5), plagioclase An_10.5Or_4.4 (N=10), chromite #Cr=0.87 (N=7), Fe-Ni alloy tetrataenite Ni=52.6 wt% Co= 2.31 wt% (N=7).