This is a piece of a meteorite that fell near El-Nakhla, in northern Egypt, in 1911. It was mysterious for many years due to its strange composition, a basaltic achondrite with abundant augite. Stones from two other falls, at Shergotty, India in 1865 and Chassigny, France in 1815, were found to be similar to each other and different from all other meteorites and Earth rocks. Eventually they became known as the SNC (shergottite-nakhlite-chassignite) group of meteorites. (Here's a picture of a shergottite.)
Only with the geochemical data sent by recent spacecraft did it become clear that the SNC group originated in the crust of Mars. And to date, about 15 different martian meteorites have been verified. Most of them are shergottites, including the famous ALH84001, the rock with (hotly contested) evidence of ancient microbes. The best gallery of these stones is at Ron Baalke's page at the Jet Propulsion Laboratory in southern California.
The latest nakhlite was found in Antarctica and reported in the August 2004 "Antarctic Meteorite Newsletter." It looks just like this.
Find more Mars links in the Mars Geology list.
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