Widmanstätten pattern
The criss-cross pattern of metal bands that appears when many iron meteorites are cut, polished and etched.
The Widmanstätten pattern is one of the most beautiful sights in meteorite science. When most iron meteorites are sliced, polished and treated with a weak acid, a lattice of crossing bands appears, like woven straw or the lines on a cut gem. The bands are crystals of two metals: nickel-poor kamacite and thin ribbons of nickel-rich taenite.
The pattern formed because the metal cooled incredibly slowly, deep inside an asteroid, often by just a few degrees every million years. That gave the crystals time to grow large enough to see with the naked eye, something that cannot be copied in a factory. The pattern is named after Count Alois von Beckh Widmanstätten, who saw it in Vienna in 1808, although William Thomson had described it a few years earlier. Gibeon from Namibia and Muonionalusta from Sweden show especially fine, delicate patterns.
Because the pattern almost never forms in Earth rocks, it is strong evidence that a piece of metal is a meteorite. Etching uses acid, so it must only be done by trained adults wearing protective gear, never by children.
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Level: Explorer Ages 10 and up