Fossil hedgehogs from Morocco.

Fossil coral is a natural gemstone that is created when prehistoric coral is gradually replaced by agate. Corals are marine organisms, and their fossilized skeletons are preserved. This fossil coral forms from fossilized deposits left behind by silica-rich water, a process that can take more than twenty million years. The correct term for fossil coral is 'agatized coral' or 'agatized fossil coral'. Agate, composed of silicon dioxide (SiO2), is a variety of naturally occurring chalcedony (microcrystalline quartz) and not a type of coral. Therefore, fossil coral should not be confused with endangered or protected reef coral or noble coral. Fossil coral is considerably harder than noble coral. Most agatized fossil corals have a matte to waxy sheen and exhibit fascinating, skeletal patterns of ancient coral, often in the shape of flowers. Fossil coral deposits are often used to make health and medicinal supplements due to their rich content of calcium, potassium, magnesium and sodium. Fossil coral, which can remove chemical contaminants such as chlorine and formaldehyde, is also used in industrial fertilizers and water purification filters.