A meteorite is any rock that survives the journey through the earth's atmosphere. They can be recognized by the presence of a 'Fusion Crust' which is a dark coating which covers the surface due to heating as the rock comes through our atmosphere. Chondrites are attracted to a strong magnet, they also have flecks of metal when cut. Achondrites are harder to recognise, and usually laboratory analsys is required to determine the origin.
There are many types of meteorite, but they are broadly classified into 4 main groups;
Irons
Iron meteorites are basically pieces of the 'core' of larger planetary bodies such as Asteroids.
They are made from Nickel and Iron.
Stony Irons
Stony Irons probably originate at the boundry and core of Asteroids they often contain a bizzare mixture of Nickel/Iron and Silicate rock.
Chondrites
There are many different types of Chondrites, this group is the most primitive of all the groups, when the first matter condensed from dust small balls where formed called 'Chondrules' these consolidated together and eventually compressed into solid rock. When Chondrites are cut and polished they reveal these ball likle chondrules. There are numerous sub groups depending upon the amount of shock melting or alteration that has gone on. Carbonaceous Chondrites are the most primitive of all known matter they contain increased amounts of carbon, and are thought to contain similar chemicals to those needed to create life, Carbonaceous Chondrites are often associated with comets.
Achondrites
These are all other meteorites that have been melted/altered completely and don't have 'chondrules', they take the form of either extraterrestrial melted/volcanic rocks (e.g Eucrites), and all rocks from other planets such as the Moon, Mars or from the larger Asteroids. There are also rocks in this group which have been melted due to severe impact.
Tektites
Tektites are melted impact debris that have completly melted and perhaps even then re-entered the earths atmosphere, They are essentially near pure Silica Glass, they remain a curiosity because of their purity, but they originated on the earth.
