What is an oriented meteorite and how can I recognise one?
An oriented meteorite kept the same face forwards as it fell, giving it a smooth cone or shield shape, flow lines radiating from the front and sometimes a rollover lip.
Most meteoroids tumble as they fall, melting evenly on all sides. A few stay stable, keeping one face pointing forwards, like a shuttlecock or a space capsule. These become oriented meteorites.
Shape. The front, which faced the oncoming air, is usually smoothly rounded, forming a cone, dome or shield shape. The back is flatter, sometimes rough or irregular.
Flow lines. On the front, fine lines of melted crust radiate outwards from the tip, showing how molten material flowed back over the surface during flight.
Rollover lip. Around the edge, melted crust may have flowed over onto the back and frozen, forming a raised rim called a rollover lip.
Crust differences. The back often has thicker, bubbly or rougher crust, because melted material gathered there in the calmer air behind the meteorite.
Regmaglypts. Thumbprint-like hollows may be arranged in patterns radiating from the front.
Examples. Oriented specimens have been found in many falls, both stony and iron. Sikhote-Alin, the iron meteorite fall in Russia in 1947, produced some beautifully oriented individuals.
Rarity and value. Only a small fraction of meteorites from a fall are well oriented. Collectors and museums prize them because their shapes show the effects of flight so clearly.
Caution. Some weathered Earth rocks can have cone or shield shapes. Look for fusion crust, flow lines and other meteorite features before concluding a stone is oriented.
If you find a possible oriented meteorite, handle it gently to preserve delicate crust features.