Electron microprobe analyses indicate that Ni-Fe spherules within impactite glass bombs from the Meteor Crater area, Arizona, contain from 20 to 65 weight percent Ni. Spherules from impactite glass at Wabar, Saudi Arabia, contain 8 to 41 percent Ni. The parent meteorites contain 7 to 8 percent Ni. The analyses indicate that glass in the vicinity of the spherules is enriched in Fe. Spherules in philippinite and indochinite tektites contain 1 to 3 and 4 to 6 percent Ni, respectively. The glass in the vicinity of tektite spherules is not enriched in Fe and contains from 3 to 6 percent Fe.

It is proposed that spherules in impactite glasses were partially oxidized prior to or during incorporation into impactite bombs. The almost Ni-free Fe oxide diffused into the glass, thus depleting the metal in Fe, and enriching the glass. Carbon dioxide and water may have contributed to the oxidation at Meteor Crater.

Spherules in tektites were not oxidized because the tektites were formed in an atmosphere with extremely low partial pressure of oxygen. A less likely alternative is that the spherules were incorporated into the tektite glass instantaneously so that oxidation was prevented.

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