Stones are similar to common terrestrial rocks in that their mineral composition is dominated by silicates, by far the most prevalent rock-forming minerals on our planet. Although some may be as large as a few millimeters in diameter, most chondrules are less than 1 mm across. In chondrites, chondrules are bound within a consolidated and fine-grained background matrix.
Chondrites are the most primitive meteorites known.
That is, they are the most ancient ones in terms of when their constituents came together to form a rock, and the most unprocessed ones in terms of how little their materials have been altered since this rock formed. Achondrites, on the other hand, lack chondrules and represent more processed materials. Chondrites, achondrites, stony-irons and irons are subdivided into groups and subgroups. These will be presented in more detail below. Falls are meteorites whose arrival on Earth was witnessed and recorded.