Prof. Fleischer publishes on impact cratering

Robert L. Fleischer, research professor of geology, wrote an article on ancient impact cratering in the December 2004 issue of Meteoritics and Planetary Science, the journal of the Meteoritical Society. Under the shock of an incoming meteorite arriving at a planetary surface, crystals in rocks can be converted into glass, a distinct, disordered material. For the 250-million-year-old Bedout crater near Australia, such glass (from a feldspar mineral) has been cited as evidence that impact produced the crater. Fleischer notes, however, that feldspar glass can also be produced by ordinary heating and cooling – one evidence being a two-pound feldspar glass, produced at General Electric, that he has been using for 40 years as a paper weight. Thus, he argues, the presence of such glass at a puzzling geological structure is not evidence of an origin by impact.