A bolide was observed approaching from 40° above the horizon at an altitude of 48 km during the night over Alberta, Canada. After 40 km of luminous flight, the bolide showered an area of 3 km with over 400 kg of fragments. The stones fell in soft snow, which protected the black fusion crust and provided great contrast to enable the locals to easily recover the fragments. The dispersion ellipse was able to be accurately mapped (see diagram below).
Bruderheim is an L6 fragmental breccia of shock stage S4 and contains partly melted metal grains and opaque veins. Based on rare gas studies, it is thought that the parent body of the L chondrites underwent a catastrophic collision 340 (±50) m.y. ago. Through studies of high-pressure minerals in an L6 sample, it was determined that this metamorphic grade occurred at least 10 km below the surface (De Carli et al., 2011). An isochron for the L chondrite parent body based on the robust HfW system provides values ranging from ~2.5 to ~14.2 m.y. after CAIs (Sprung et al., 2011). The Bruderheim specimen shown above is a 7.0 g cut fragment with black fusion crust.
Photo courtesy of the Smithsonian Institution, Washington D.C.