Meteorites formed from the same dust and gas as Earth did, and they're made of pretty much the same minerals as Earth (typically olivine, pyroxene, and feldspar). However, most meteorites were formed under different conditions of heat and pressure than Earth was, and they're usually identified by their resulting physical characteristics rather than their chemical properties.

Some meteorites (primitive chondrites) are considered relatively unaltered material from the formation of the solar system. At the other extreme, metallic iron could only accumulate at the core of something planet-sized, something which must have been shattered by a large impact, resulting in iron meteorites. A few rare meteorites have come to Earth from the moon and Mars, having been ejected into space by asteroid impacts; these meteorites most closely resemble Earth rocks, having once been planetary crust (or mantle in the case of the moon), and can best be identified by their chemical composition.

First link is an overview of meteorite types; second includes a graph showing chemical ratios of meteorites and Earth rocks.
Source(s):
http://meteorites.lpl.arizona.edu/composition.html
http://www.meteorites.wustl.edu/metcomp/index.htm

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