Ammonite and Black Onyx NecklaceThis Ammonite and Black Onyx Necklace brings together a fossil from ancient oceans and a striking natural mineral. The piece features a fossilized ammonite paired with polished black onyx, both set in sterling silver. Ammonites were spiral shelled marine mollusks that lived during the Mesozoic era, and their shells were preserved through fossilization over millions of years. Black onyx is a variety of chalcedony, a microcrystalline form of quartz