Formed as silica-rich solutions flow repeatedly into cavities in volcanic rock, building up layer by layer. The orange is determined by the oxidation state of iron.

Agate is among the world's oldest gemstones—worked specimens have been recovered from Egyptian sites dating to 3000 BC. The name ""agate"" derives from the Achates River in Sicily, where the ancient Greeks first found it.

Even from the same vein, no two patterns match. The Earth's chemistry shifted moment by moment as the layers settled. Those shifts themselves became the pattern.