Meteorites are solid bodies of the inner solar system that have impacted Earth. Here are a few amusing links regarding the finding of meteorites on Earth’s surface:
Meteorite identification questions: http://meteorite.museums.ualberta.ca/identify.pdf
Meteorwrong: http://meteorite.museums.ualberta.ca/browseresults.php?txt=5 – a collection of things that are commonly mistaken for meteorites, but are definitely not.
Most originate from the asteroid belt, with some coming from Mars and the Moon. There are three types of meteorites:
1. Stony meteorites: dominated by Fe and Mg, and include chondrites (contain small spherules of silicate materials within a finer matrix and are largely representative of primitive planetesimal chemistry – carbonaceous chondrites, which contain more volatiles than normal ones, are used to date the age of the solar system), and anchondrites (lack the small spherules and look very much like mafic igneous rocks – probably the product of melting to form a differentiated crust on parent planetesimals)
2. Stony-iron meteorites: rare, and probably formed at or near a mantle/core boundary and dislodged by impact.
3. Iron meteorites: Fe and Ni metal, they are very durable and therefore quite frequently recovered. They are also the product of differentiation and cooling.
Main belt asteroids are located between Mars and Jupiter, and will stay there unless knocked off course. Apollo asteroids are ones whose orbit crosses that of Earth. They come in a range of compositions similar to meteorites.
The asteroid belt may have been formed in two ways: either it’s remnants of broken up planetesimals or (the more favoured theory) never accreted to begin with (which would explain the existence of chondrites). The reason the asteroids in the belt never accreted may have something to do with the gravitational pull of Jupiter.