Widmanstätten patterns

Why not every iron meteorite shows them

Very low or high nickel contents and other textures may not produce the classic pattern. The result also depends on cut orientation, preparation and etching.

Crystal growth over millions of years

As nickel-bearing iron melt cools extremely slowly, the initially uniform taenite phase becomes unstable. Lower-nickel kamacite exsolves along specific crystal planes, producing the intersecting lamellae of a Widmanstätten pattern.

Such large lamellae require cooling rates possible deep inside asteroids over millions of years. Kamacite bandwidth helps classify octahedrites but also depends on nickel content and cooling history.

Revealing and interpreting the pattern

The pattern appears only after a cut surface has been flattened, polished and etched with a suitable acid. The orientation of the cut through the original crystal changes its angles and appearance.

Not every iron meteorite shows the classic pattern: hexahedrites and nickel-rich ataxites have different textures. Artificially treated metal can also show lines. The pattern is strong structural evidence but not sole proof of authenticity without chemistry and provenance.