What do meteorites look like?

Meteorites have a few special clues that can help you recognise them. Learning these clues is the first step to becoming a meteorite detective.

A dark, thin skin

When a meteoroid rushes through the air, its outside melts. When it slows down, that melted layer quickly cools into a thin skin called a fusion crust. On a fresh meteorite the fusion crust is usually black or dark brown and can be dull or slightly shiny. It is very thin, normally less than a millimetre, a bit like the shell on a chocolate-covered sweet.

If part of the crust is chipped off, you may see the inside of the stone, which is often a lighter grey colour. A dark skin with a paler inside is a good clue.

Over time, rain and air make fusion crust rusty and brown, and in deserts it can be worn away completely. So older meteorites can be harder to recognise.

Thumbprints and shapes

Meteorites are rarely perfectly round. They are often lumpy, with smooth, rounded edges. Some have shallow dents on their surface, as if someone had pressed a thumb into soft clay. These dents are called regmaglypts, but many people simply call them thumbprints. They form when the air melts and scoops away the surface unevenly during the fiery fall.

A few meteorites are shaped like a cone or a shield. These kept pointing the same way while they fell, so the front was shaped by the rushing air.

Meteorites do not have bubbles or holes like a sponge. Rocks full of holes are usually volcanic rocks or leftover waste from old furnaces, not meteorites. Some fresh stones also show thin lines or ripples where melted rock flowed across the surface before it froze, called flow lines.

Heavy and magnetic

Most meteorites contain some iron-nickel metal. That gives them two more clues.

First, they often feel heavier than you would expect for their size. Iron meteorites feel extremely heavy, and many stony ones feel heavier than ordinary rocks too.

Second, a magnet will usually stick to them, or at least be pulled towards them. A simple test is to hang a strong magnet from a piece of string and see whether it swings towards the rock.

But be careful: these are clues, not proof. Some Earth rocks are heavy and magnetic too, and a few rare meteorites, such as many from the Moon and Mars, hardly react to a magnet at all. Only an expert in a laboratory can say for sure whether a rock is a meteorite.

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