Dho 778

Diogenite, anomalous
(≥90 vol% orthopyroxene)

standby for dhofar 778 photo
Found October 2000
18° 43.525′ N., 54° 43.829′ E.

A single lightly weathered (W1) stone, weighing 156 g, was found in the desert of Oman by a German team. It was classified by Dr. J. Otto at the Institut für Mineralogie, Universität Freiburg, as one of the most highly shocked diogenites yet discovered, with a shock stage of S4. This breccia exhibits a fragmental texture, which has been interpreted to be a characteristic of impact ejecta. For more details on the formation of diogenites visit the Johnstown page. To see an alternative classification system for the diogenites and dunites based on mineralogical and petrographical features, proposed by Beck and McSween (2010) and modified by Wittke et al. (2011), click here.

The oxygen isotopic composition for Dhofar 778 was determined by Greenwood et al. (2017), and the plot occupies a distinct space on an oxygen three-isotope diagram (see below). They suggest that this anomalous oxygen isotope composition may be attributed to contamination by an exogenous component, but note that further analysis should be conducted. standby for o-isotopic diagram
Diagram credit: Greenwood et al., Chemie der Erde, vol. 77, p. 25 (2017)
‘Melting and differentiation of early-formed asteroids: The perspective from high precision oxygen isotope studies’
(open access: http://dx.doi.org/10.1016/j.chemer.2016.09.005)
The photo above shows a 0.88 g half slice of Dhofar 778, which exhibits profound shock-veining. Increased magnification reveals that fragmentation is present to a very fine scale. It is thought that the melt veins were formed and quenched within a few microseconds. The top photo below is a high resolution image of this diogenite, courtesy of Stephan Kambach. This is a highly polished section revealing a greenish color similar to that of Tatahouine. The bottom photo below shows the fusion-crusted side of the main mass. dhofar 778
click on image for a magnified view

Photo courtesy of Stephan Kambach

standby for dhofar 778 photo
standby for dhofar 778 photo
Photos of the complete stone shown courtesy of Stephan Kambach

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