End Cut of the Enigmatic NWA 1878 Meso-B Meteorite

A large metallic nodule dominates the piece. Mesosiderites are a class of stony-iron meteorites that consist of roughly equal parts of metallic nickel-iron and silicate. There are only six mesosiderites with the designation of class B. Unlike pallasites, which formed at the boundary of the stony mantle and molten core of an asteroid that was later disrupted by a collision, the formation of mesosiderites is less well understood. One leading model is that this material formed when the semi-molten core of one asteroid collided with the solidified basalt-strewn surface of a larger asteroid. This specimen appears to have been collisionally melted after it formed; coagulated metal nodules were surrounded by silicate-rich melt.

NWA 1878 was found in 2000 in the Sahara Desert and is “relatively coarse grained, with an unbrecciated, plutonic igneous texture with subequal amounts of metal and silicates.”