This is an image of a sample of cratonic mantle root from Kimberley, South Africa. The rock consists of dark green olivine, whitish-green enstatite, emerald green diopside and purple garnet. (Credit: David R. Bell / ASU)
From Science Daily:
ScienceDaily (Sep. 2, 2010) — Earth today is one of the most active planets in the Solar System, and was probably even more so during the early stages of its life. Thanks to the plate tectonics that continue to shape our planet's surface, remnants of crust from Earth's formative years are rare, but not impossible to find. A paper published in Nature Sept. 2 examines how some ancient rocks have resisted being recycled into Earth's convecting interior.
Read more ....