The Classification and Main Types of Meteorites
Many meteorites have been discovered over the years which, in many cases, can give an insight into the creation of the universe. All these meteorites can be grouped together by looking at the various characteristics they have in common, such as the structures of the different meteorites and the isotopic properties of the meteorites. When trying to classify meteorites, they are generally identified as one of the three main groups of meteorites: Iron, Stony and Stony-iron. Each group has its own properties which makes them unique to one another. These groups can be divided further more into smaller groups.
Iron meteorites originated from the core of asteroids and can be divided in to many groups depending on their characteristics: list groups
Group IIAB Iron meteorites have low concentrations of nickel compared to other iron groups. The structures vary from Hexahedrites to coarsest octahedrites. Hexahedrites have the lowest concentration of nickel in their structure. IIAB iron meteorites are thought to be highly reduced materials due to the absence of phosphates, low concentration of nickel and the occurrence of graphite [H]. Group IIIAB Iron meteorites are the largest group of Iron meteorites. Meteorites in this category have medium octahedrite structure (most common iron meteorite structure due to certain amount of Nickel concentration). IIIAB iron meteorites are thought to be oxidized materials due to the high abundance of phosphate [H]. Group IVA Iron meteorites are the third largest group and exhibits octahedrite structures. This group of meteorites has an unusually low ratio of Ir/Au. Apart from this the meteorites are not very volatile [H]. Group IVB iron group only contains 13 meteorites but have unique qualities. Out of all the iron meteorite groups, IVB is considered to be the least volatile. This group also contains high concentrations of iridium, rhenium, and osmium [H].Group IAB, IIICD, and IIE irons (also known as nonmagnetic iron) are considered as silicate bearing iron meteorites which show different properties compared to other iron groups. The metals in group IAB and IIICD show high concentrations of nickel, gallium, and germanium compared to other groups. Group IIE is a smaller group with metals which have a range of properties when looking at the structures and silicates. [H]
Iron meteorites from the same core should have a similar cooling rate. The cooling rate from group to group is different but consistent. This is the case for all groups apart from IVA. [F]
One way to classify iron meteorites is to look at the crystal structure. Iron meteorites can be grouped in to 3 main categorise when looking at crystal structures: Octahedrites, Hexahedrites and Ataxites.
Octahedrites have a special and distinguishable characteristic called the Widmanstätten lines. These lines consist of the kamacite and taenite lamella growing together and can be seen when the...