Fusion crust

The rapid deceleration a meteorite experiences as it travels into the Earth's atmosphere causes an intense heat. This heat melts the surface of the meteorite, forming a thin layer known as the fusion crust. The fusion crust is usually black or dark grey and generally no more than a millimetre thick. Small gas bubbles and 'dribbles' from the air resistance can also sometimes be seen. The fusion crust makes recent and unweathered meteorites easy to identify.

Internal features

Where the fusion crust has been worn away, internal features become more important. The most common type of meteorite found in temperate places like the UK are iron meteorites, because they stand out as different from our regular rocks. They are also strongly magnetic and very dense. It is difficult, however, to distinguish industrial iron from iron meteorites without chemical analysis.

The most common type of stony meteorites, chondrites, can be identified by millimetre-sized spherical objects contained within a finer grained material. These fine grain 'chondrules' often contain metal and can be magnetic. There are however many terrestrial rocks that resemble stony meteorites, and again chemical analysis may be needed.

Look-a-likes

Perhaps the commonest objects mistaken for meteorites are spherical, rusty looking, marcasite nodules. Consisting of iron sulphide, marcasite is quite dense and has rounded protrusions that can give a melted appearance. It is however less dense than iron meteorites and is commonly found in chalk.

Industrial slag also has a melted appearance and usually contains bubbles. It is, therefore, commonly mistaken for meteorites. Slag, however, has melted all the way through, rather than having a very thin crust, and often contains large gas bubbles.

Meteorite identification checklist