Feather Pyrite doesn't start out as pyrite at all. What actually happens underground is stranger: fine-grained pyrite slowly replaces older pyrrhotite crystals, atom by atom, while somehow preserving the original crystal's thin, tabular, fan-like shape.
The result is a stone that carries pyrite's metallic silver-gold luster but arranged in soft, feathery, almost frost-like patterns instead of pyrite's usual cubic sparkle — a mineral wearing another mineral's old shape.
That unusual origin is exactly why the pattern reads the way it does — radiating, fan-shaped clusters spreading across a dark metallic base, closer to a frost pattern on glass than a typical faceted stone.
It's also worth knowing that "feather pyrite" and "marcasite jewelry" often get lumped together by shoppers, but they're not the same thing — most marcasite jewelry on the market is actually cut pyrite too (true marcasite is too brittle and unstable to set reliably), so the visual overlap between the two names isn't a coincidence.