Nothing Ordinary About Ordinary Chondrites
The large meteorites seen in museums are often made of nickel iron. That might give one the impression that most meteorites are solid metal. But, the fact of the matter is that most meteorites are made of stone. In geology we talk about stones being made up of minerals. It is that way with meteorites as well.In most cases the minerals found in meteorites are ones that are also found on Earth. There are some exceptions. Some meteorite minerals are only found in rocks from space. As just a side note here there has never been found an element in meteorites that does not occur on Earth.
What is different in the way the minerals make up meteorites is that they are found as small droplets of mineral crystals called chondrules. These structures exist because the minerals cooled in such low gravity that they remained round spheres. On Earth or any large body in space the gravity will cause flat layers of rock to form as the minerals cool instead of small isolated round spheres.
Chondrites are the type of meteorites that have chondrules. Ordinary Chondrites are by far the largest of the meteorite groups. There is nothing very ordinary about any meteorite as it is the rarest of material on the Earth. But the name Ordinary Chondrite refers to chemistry and structure of this group of meteorites. With in the large type are three sub-groups that are distinguished by the amount of nickel-iron they contain. The H chondrites have a high metal content in the form of tiny metallic grains scattered throughout the rock. The L chondrites have a low metallic iron content with far less of the metal grains being present in the rock. The last sub group the LL chondrites have very slight amounts of metallic nickel-iron and very little iron bound up in mineral form as well.
Besides the Ordinary Chondrites there are other chondite types. The R, E and Carbonaceous Chondrites are also meteorites with chondrules. They are very different from Ordinary Chondrites. They show different alteration during their time in space. They often have a predominate mineral whereas the Ordinary Chondrites will have a more mixed makeup of several minerals.
