CBa, bencubbinite

standby for nwa 4025 photo
click on photo for a magnified view

Purchased August 2005
no coordinates recorded

A group of sixty-nine small, paired, stone fragments, having a combined weight of 745.5 g, were recovered in the Sahara Desert by a Moroccan hunter. Further searches of the area have yielded no additional fragments. All of these fragments were subsequently purchased by H. Strufe, and a sample was submitted for analysis to the Museum für Naturkunde, Humboldt University, Berlin, (A. Greshake). Northwest Africa 4025 was classified as a rare CBa bencubbinite.

Northwest Africa 4025 exhibits very close similarities to the type specimen Bencubbin, and has a shock stage of S3 and a weathering grade of W2/3. A visual comparison was conducted between specimens of NWA 4025 and the previously found Saharan CBa chondrite, NWA 1814; it was clearly demonstrated that they are not paired. Northwest Africa 4025 closely resembles the Bencubbin meteorite, while NWA 1814 manifests some characteristics of the CBa chondrite Gujba. Moreover, The degree of terrestrial alteration on the outer surface of NWA 4025 is generally higher than that on NWA 1814. An O-isotopic analysis indicates that a close relationship exists between this bencubbinite and the CH chondrites.

The CB, CH, and CR chondrites constitute the CR clan, comprising groups which likely formed in the same isotopic reservoir under similar conditions in the solar nebula. The best current evidence supports an origin for these late-formed metal-rich carbonaceous chondrites in an impact plume generated by a collision between planetary embryos (Krot et al., 2009). Following condensation of the various components, they were aerodynamically sorted according to their velocity, size, and density as they spread out into the nebular gas in a typical fan-shaped pattern. It was calculated by Morris et al. (2012) that in ~1% of the impacts the host planetesimal would travel in the direction of the impact plume, sweeping up some of the aerodynamically sorted ejecta within a short time period measured in weeks. They reason that this reaccreted material would have been mixed with existing crustal components to form a layer many meters thick. See the HaH 237 page for a more detailed scenario of the CB group formation process ascertained by Fedkin et al. (2015) through kinetic condensation modeling.

The specimen of NWA 4025 shown above is a 7.6 g prepared end section (half individual). Pictured below are two of the sixty-nine recovered fragments constituting this meteorite.

standby for nwa 4025 photo
Photo courtesy of the J. Piatek Collection