Iron meteorites are made up of pure nickel and iron metals and are thought to originate from within the metallic cores of asteroids. Iron meteorites fall very rarely, but are easier to find because they can survive re-entry relatively intact, are very resistant to weathering and look very different to normal rocks, having more of a melted appearance.
Stony meteorites are largely made of rock but can also contain small amounts of iron. This category is split up into chondrites and achondrites.
Chondrites are the most common type of meteorite. They are made up of circular mineral blobs called chondrules that formed in space billions of years ago and became clumped together over the years. They are the oldest rocks that we know of and have not been altered or changed since their formation, and so are an important type of meteorite to study to learn more about how the solar system and planets formed.
Achondrites are meteorites that contain minerals which have been melted, changed and altered since they were formed, which makes them different to chondrites. This process of change happens because they are formed on bodies with enough mass to support a molten interior. These can include large asteroids, the Moon and even Mars. Achondrites are much younger than chondrites and have a variety of different textures and mineral compositions which can teach us about the formation history of their parent body.
Stony-Iron meteorites are made up of almost even amounts of metallic and rocky material. They are thought to have formed by mixing between metal cores and the rocky magmas within asteroids.This makes them extremely rare because there is only a small region inside asteroids where metallic and stony material can mix. There are two types of stony-iron meteorites; pallasites and mesosiderites
Pallasites are mostly metallic, however also contain large, translucent crystals of olivine. They come from the boundary between the metallic core of an asteroid and the surrounding rocky magma which makes them very rare but extremely interesting. They are some of the most visually striking meteorite specimens ever discovered.
Mesosiderites are composed of even amounts of metallic elements and sillicate minerals. Unlike pallasites, the crystals within mesosiderites are made of pale silicate minerals and are not very large, giving the meteorite a speckled and irregular appearance. Because of the presence of silicate minerals and the small size of the crystals, scientists believe that mesosiderites probably form when magma mixes with the core during a collision.