Leung, I.S., Winston, R. and Abbott, D.H., 2004, May. Silicon carbide from the Canyon Diablo meteorite and the Ewing Impact Structure. In AGU Spring Meeting Abstracts.
One hundred years ago, Henri Moissan reported his discovery of silicon carbide (SiC) in the Canyon Diablo Meteorite. Since then, other researchers tried, but failed to replicate his findings. In our study of highly oxidized samples of the Canyon Diablo Meteorite, we found two carbon nodules, respectively 1 cm and 2 cm in size; the latter is no longer in the matrix which had disintegrated into rust. We found several SiC crystals in these nodules. Most of them show color zoning, planar deformation features (PDFs), black inclusions and black rims. The X-ray diffraction pattern of a 60-micron crystal showed a 6H polytype structure for the host in addition to a weak lattice, related to that of the host by a 2-degree rotation about the a-axis. We believe that the weak lattice was derived from the PDFs. We also report here the first find of SiC from deep sea sediments on the rim of the Ewing Impact Crater, located near the Equator at about 10 degrees east of the longitude of Hawaii. The SiC crystals also contain PDFs. An X-ray diffraction study showed 6H structure for the host, and 15R structure for the PDFs. Thus, 15R seems to be the high-pressure phase, a potentially useful marker for shock deformation events. Implications of our study are as follows. (1) Because all occurrences of terrestrial SiC are associated with kimberlites, SiC found at impact sites might have originated from space, or, by transformation of terrestrial materials by impact mechanisms. (2) The extreme sturdiness of SiC might enable it to resist alteration, long after other impact markers have decomposed. (3) Hence, SiC crystals, with or without PDFs, though small in size and few in number, might provide clues for deciphering possible relationships between impact events and global extinction of species.