The shape of a meteorite is never the same twice and can never be perfectly spherical. Sharp points and edges will be smoothed by melting during flight through our atmosphere, leaving the appearance of a smooth, angular black rock.
The black colouration is called fusion crust – this is a thin but tough "skin" all over the meteorite, and a remnant of the heating and melting during flight.
Freshly fallen meteorites, quickly recovered after they fall, will be black over all or most of their outer surface. If they hit a particularly hard surface on the ground, they will probably chip or break into several pieces. When the interior of the stone is exposed, a stark contrast between the light coloured stony interior and the dark black outer fusion crust is very noticeable.
Quickly recovered after it fell, this meteorite shows fresh, black
fusion crust and a light coloured stony interior.
The commonest type of stony meteorites contain iron metal - either as small and shiny flecks mixed within the stone, or as microscopic pieces too small to be seen.
A true meteorite will almost always draw a magnet.
This metal content is a great help in identifying a meteorite – BUT, it's also a big problem for the long-term survival of meteorites. In the wet and humid Great British Outdoors, the killer rust can attack and disintegrate a meteorite in exactly the same way as it can disintegrate Earthly iron.
The effects of the damp British climate are beginning to rust the surface of this stony meteorite.
A few more weeks of rain and this stone would have been entirely rust-red.
Unless a meteorite is seen to fall and discovered within a few days - or weeks at the most- the exterior fusion crust of a meteorite will show signs of rusting on its surface. Depending on exactly how long it's been lying on the ground and exposed to the elements, the fusion crust may appear orange with small and faint patches of the original black. After a longer time, it may rust enough to appear completely orange, or it may have weathered away altogether, leaving behind a piece of rock that's entirely stained with flaking brown rust.
Long exposure to our damp climate has completely rusted this stony meteorite, inside and out.
This is a very good example of how a newly found British meteorite will look.
Notice the score line near the centre – a farmer hit this meteorite with his plough!
Despite the ugly rust, these meteorites still have great interest to scientists and collectors alike. It will still contain enough iron to attract a magnet, and small meteorites will jump onto a magnet with a definite "click".
Want to find your own meteorites, but don't know where to start? Try Rob's hints for hunters