The Florida State Stone Agatized Coral

Agatized coral occurs when silica in the ocean water hardens, replacing the limy corals with a form of quartz mineral known as chalcedony. This long fossilization process (20–30 million years) results in the formation of a "pseudomorph," meaning that one mineral has replaced another without having lost its original form. In 1979 agatized coral was designated the official state stone.

Agatized coral is found in three main Florida locations: Tampa Bay, the Econfina River, and the Withlacoochee/Suwannee River beds.