The Chuckwalla, CA, IAB iron contains preterrestrial impact-produced diamonds with sphalerite

Details The Chuckwalla, CA, IAB iron contains preterrestrial impact-produced diamonds with sphalerite The Chuckwalla, CA, IAB iron contains preterrestrial impact-produced diamonds with sphalerite

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.457c&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 457

Computer Science

Chemical Composition, Diamonds, Iron Meteorites, Meteoritic Microstructures, Shock Loads, Zincblende, Crystal Structure, Inclusions, Metallography, Mineralogy, Neutron Activation Analysis

Scientific paper

A 1.8-kg, roughly hemispherical shaped, iron meteorite was found by Melvin English on a slope of the Chuckwalla Mountains, Kern County, California. Neutron activation analysis yields 68 mg/g Ni, 4.6 mg/g Co, 104 micro-g/g Ga, 22 micro-g/g As, 2.9 micro-g/g Ir, and 1.6 micro-g/g Au. These values match well those for the average of IAB irons of this Ni content, with the exception that As is high by a factor of 2. Metallographic examination revealed that Chuckwalla is a cohenite-rich, coarse octahedrite that has been severely shock-altered. Superimposed on this preterrestrial shock-altered internal structure is a about 2-mm-thick heat-altered zone along the entire exterior edge of the about 14 sq cm surface. Schreibersite and taenite are melted close to the exterior edge of the heat-altered zone, but not in its interior or further into the slice. While cutting Chuckwalla to obtain material for study, the saw blade penetrated with unusual difficulty and was finally stopped. A black, 0.75-mm-diameter inclusion was found at the most forward point of this first cut. It was isolated from metal and subjected to X-ray examination. Powder diffraction data indicate both cubic diamond (diamond) and hexagonal diamond (lonsdaleite). All reflections are broad, indicating very small crystallines. A second carbonado (290 x 200 microns) was found in situ when over half of the large slice was prepared for metallographic examination. It is in association with two types of material. One appears to be a single-phase, gray mineral. The second type of area appears to be two-phase on a scale of a few micrometers or less and contains numerous small black inclusions and a small area of kamacite. It appears to have formed by shock melting. A second inclusion containing the two types of material is present in the same section, as are two smaller inclusions of the single-phase material. Of the three Fe meteorites that are now known to contain shock-produced diamonds, the shock event in two cases took place preterrestrially, probably at the time of the break-up of their parent body.

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