A rocky body of extra-terrestrial origin that has survived the passage through the atmosphere (see shooting star) and therefore falls to earth . It is thought that a huge meteorite (several kilometres in diameter) was responsible for the disappearance of the dinosaurs 65 million years ago. The mass of meteorites falling to Earth per year is estimated at 10 000 tonnes.
There is a wide variety of meteorites and to sort these out, they have been classified into three main categories.
There are rocky ones, metallic ones and intermediate ones that are called mixed.
According to the interpretation accepted today, these differences in mineralogical composition reflect different conditions in the formation and evolution of bodies in the solar system.
Credits: Stephane Erard and Aurélie Le Bras (obspm.fr).
In the case of an asteroid at least a few hundreds of kilometres in size, the quantity of radioactive elements initially present would have been enough to heat it strongly, causing partial fusion with the formation of a ferrous core at its centre with a mantle around giving rise to magmatic and volcanic processes.
During violent collisions, some asteroids were pulverised in the shock and this may well be the origin of metallic and mixed meteorites, depending on whether they are composed of an iron-nickel alloy, like the siderites, or a mixture of the latter with other minerals, like the pallasites.
In the latter case, olivine crystals are observed trapped in the metal. It is thought that this may be a piece of the layer at the interface between the core and the mantle of these large asteroids. The same types of rock probably occur at this same interface on earth.