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Ammonite is the fossilized shell of ancient sea amminoids and nautiloids, ancestors of the present-day pearly nautilus. An ammonite fossil formed when the ammonite shell absorbed minerals from silt. Centuries of sediment layers compressed the minerals to rock. The organic gem coral is the skeleton of coral polyps which live in the sea. Dull when harvested, it can be polished to a high shine. Red and pink varieties are generally found in warm Asian and Mediterranean waters. Coral has been carved in China for 2,000 years and was used medicinally and as an amulet in other ancient cultures. Sea bamboo is a vivid red gem from the coral family. Fossilized coral dates from the Ordovician period of prehistory and displays beautiful colors and a gorgeous starburst pattern when polished. Prehistoric sharks' teeth may be black, brown, or gray, depending on the minerals in the soil in which they have been buried. Sand at the bottom of the ocean preserved and fossilized the teeth, and wave action uncovers and washes them ashore. Many fossil shark teeth have been collected from the coastal areas of the Gulf of Mexico. Trilobites were ancient sea-dwelling arthropods that lived in shallow coastal areas. They survived for approximately 350 million years beginning in the Cambrian period and are the earliest animal to exhibit evidence of eyesight in the fossil record.
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