DHOFAR 979


Ureilite
Monomict/Unbrecciated
Olivine–pigeonite

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Found January 8, 2004
19° 45.4' N., 54° 56.2' W.

A single complete stone weighing 1,063 g was found in Oman by Mike Farmer. Coincidentally, this achondrite was found only ~30 m from an oriented chondrite. Analysis and classification was completed at Northern Arizona University (J. Wittke, T. Bunch), and Dhofar 979 was determined to be an olivine–pigeonite ureilite.

Dhofar 979 contains wormy graphite between grains and within olivine, and does not exhibit evidence of a significant degree of carbon–silicate reduction/smelting processes (FeO + C = Fe + CO) typically seen in other ureilites. Smelting is usually apparent as an increase in free Fe-metal content, a decrease in carbon content through loss of CO, and an increase in iron carbide content. Notably, this ureilite does not have the hardness observed in other ureilites. Dhofar 979 has a reduction value of R1, which could be consistent with either formation at great depth, where higher pressures inhibit the smelting reaction, or formation at lower temperatures. It was also shown that the pristine graphite in this ureilite has not been converted to diamond, a transformation which typically occurs through impact shock forces while in proximity to the surface.

A synopsis of current models for ureilite formation is presented on the Kenna page. The specimen of Dhofar 979 shown above is a 2.03 g partial slice. The photo below shows the complete Dhofar 979 mass in situ prior to recovery.

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Photo courtesy of Mike Farmer—Mike's Meteorites and Tektites

The magnified images shown below, courtesy of John Kashuba, show yellowish, translucent olivines forming 120° triple junctions (left), along with crystals of scarce FeNi-metal between silicate grain boundaries (right). The bottom photo is an excellent petrographic thin section micrograph of Dhofar 979, shown courtesy of Peter Marmet.

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Photos courtesy of John Kashuba.

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click on photo for a magnified view
Photo courtesy of Peter Marmet


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