Coral

Corals are marine invertebrates. They are usually found living in compact groups or 'colonies' of genetically identical polyps in tropical seas and oceans, and are very important in the building and maintaining of coral reefs, which support many forms of marine life. Their hard exoskeletons are formed by secretions of calcium carbonate.

Uses
For thousands of years, coral has been used in medicines and jewellry. Red coral is especially prized and regarded as auspicious in some cultures, though sadly, it has become rare due to overharvesting.

In Evernight
In the Evernight series, coral, being a material that was once alive, is a powerful object for wraiths. Bianca Olivier is able to use a coral bracelet gifted to her by Lucas Ross to take on a corporeal form and retain it as long as she is holding or wearing the bracelet.