Meteors and MASS NMR: it's a hit!

A bit of stishovite found at a site where scientists are trying to prove that an asteroid once smacked into the earth would do wonders for their case. The silica mineral has been found in nature only where meteors have hit and created a large impulse of pressure. But testing for stishovite has not been an easy process. The mineral typically comes in such small quantities that it must be concentrated with chemical techniques that often destroy the crystals. And when X-ray diffraction is done on the sample, the stishovite signal is easily obscured by other elements.

In an upcoming issue of METEORITICS, John F. McHone and co-workers at the University of Illinois in Urbana discuss another technique for hunting stishovite: magic-angle sample-spinning nuclear magnetic resonance (MASS NMR), in which the NMR device, normally used in the study of liquids, is "fooled" into treating a spinning sample of ground-up solid material as a liquid. With this method, the researchers clearly detected stishovite in a sandstone rock from a crater in Arizona. "We were able to take a rock right off the ground, grind up, stick it in the NMR and voila! Out came a spectrum," says McHone.

Unfortunately, the technique cannot be used with magnetic minerals, which are common in meteorites and are also found in the clays of the Cretaceous-Tertiary (K/T) boundary that has attracted so much debate over whether an asteroid caused mass extinctions 85 million years ago (SN: 6/2/79, p. 356). McHone, however, believes that this problem may be solved in the near future. He also says that no stishovite was detected in a K/T sample, but it may have been destroyed by the present preparation method.