Fossil coral is a natural gemstone that is created when prehistoric coral is gradually replaced with agate. Corals are marine animals, and it is their skeletons that are fossilized and preserved. The fossil coral forms through hardened deposits left by silica-rich waters. The entire process can take over 20 million years. The proper name for fossil coral is “agatized coral” or “agatized fossil coral.” Agate, with its silicon dioxide composition (SiO₂), is a variety of naturally occurring chalcedony–or microcrystalline quartz–rather than a type of coral. For this reason, fossil coral should not be mistaken for endangered or protected reef coral or precious coral. Most agatized fossil coral exhibits a dull to waxy luster and interesting skeletal-like ancient coral patterns, most often appearing in flower shapes.

According to metaphysical beliefs, fossil coral is a grounding stone good for bringing about change.