"Half-Baked Asteroids Have Earth-Like Crust"

This article, written back in January of 2009, discusses the then recent discovery of two meteorites and what this means for the history of our solar system. The meteorites were ancient asteroid fragments made up of feldspar-rich rock called andesite and were discovered during the Antarctic Search for Meteorites of 2006/2007. Andesite is a common indigenous rock on Earth, which is created through the collision of tectonic plates in the creation of volcanoes. As the lead author of the discovery, James Day of the University of Maryland, notes, "No meteorites like this have ever been seen before." The meteorites that scientists believe the samples came from are hypothesized to be 4.5 billion years old (very close to the age of our solar system) and have a diameter of slightly over 100 kilometers, just big enough for the rock to partially, not completely, melt.The importance of these samples is that previous to this discovery, this type of rock had not been discovered elsewhere in our solar system, other than on planet Earth. The rocks have compositions very similar to Earth's andesite continental crust, which indicates that "the formation of planet-like andesite crust has occurred by processes other than plate tectonics on solar system bodies" (Day 1).

http://www.sciencedaily.com/releases/2009/01/090107134526.htm