Tektites are a kind of meteorite thought to form after a comet or large stony object strikes the Earth. A large amount of the Earth's material at the impact site is melted and splashed all the way out of the atmosphere into space. As the material reenters the atmosphere, it melts again and gets pitted and polished by the turbulence of the air. This tektite is from the Australasian strewnfield. It's basically a brown glass, a meteorite from Earth. It's conceivable that pieces like this could reach other planets, like Mars, just as Martian rocks have been found here.
Some scientists prefer to argue that tektites come instead from the Moon, where energetic volcanoes propel them into space. There's evidence for that, but where does the energy for such a violent eruption come from? More research is needed, but until some large geological problem depends on tektites, researchers will be few and progress will be slow.
Other galleries:
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society