We found 5 crystals of SiC (size 70-150 microns) in a black nodule (1 cm in size), composed mostly of disordered graphite and diamond/lonsdaleite. We present in this paper our finding of three varieties of SiC crystals in the Canyon Diablo meteorite. Recently, occurrence of SiC in carbonaceous chondrites has been confirmed. Thus, an intriguing mineralogical controversy ensued to this day. Scholars of the same meteorite, unable to find SiC, believed that Moissan's sample might have been contaminated by synthetic SiC used in tools and abrasives. Kunz coined the mineral name moissanite in 1904. Silicon carbide (SiC) was reportedly found in the residue of a 50-kg sample of the Canyon Diablo meteorite dissolved in acid by Henri Moissan, and, in his honor, George F. Historical and New Perspective of Moissanite in the Canyon Diablo Meteorite We also X-rayed individual grains, and have identified several hexagonal polytype structures as well as the cubic form (3C polytype). Under a binocular microscope, SiC crystals can be spotted easily by their adamantine luster, color (blue, green, beige, etc.), and high birefringence when placed between crossed polarizers of a petrographic microscope. After removing the large metal fragments, we put a small amount of the fine black grains in a Petri dish with acetone, then swerved the dish to scatter the grains sparingly on the bottom of the dish. We broke up the carbon nodule with a sharp tungsten carbide chisel and hammer. We chose samples containing a carbon nodule composed of graphite, diamond-lonsdaleite, and SiC grains in the iron matrix. We report here a simple method we used to separate SiC crystals from the meteorite.
The significance of SiC in the Canyon Diablo cannot be revealed unless we have abundant data from pristine samples, enough for us to classify them into presolar or other types. Some have been identified as presolar grains. SiC grains have been found in primitive meteorites and interplanetary dust particles. This notion hampered further work on abundant materials housed in museums. Hence, the occurrence of SiC in the Canyon Diablo remains in doubt, and any proposal to investigate this problem was discouraged and regarded as predictably unproductive. Subsequently, many erroneous reports appeared when the polishing compound (synthetic SiC) was mistakenly considered by researchers as a natural mineral associated with, rather than a contaminant of many rock types. Moissan did not report finding the cubic form of SiC. In a study of a large block (53 kg) of this meteorite, Henri Moissan reported his findings of green, hexagonal crystals of silicon carbide (SiC) which was given the name moissanite the following year by George Kunz (1905).
The Canyon Diablo is an iron meteorite whose collision with Earth created Meteor Crater in Arizona. Pristine Samples of Silicon Carbide Separated From the Canyon Diablo Meteorite
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