An amorphous gem, like jet, amber, or ivory, does not have a regular internal structure, like those gems that fall within the seven crystal systems . An amulet is a protective charm that is worn. It is worn in the hope of protecting the wearer from evil or illness or to bring the wearer good luck. The amulet above is turquoise with carved inscriptions, and set in gold. Coral is an animal that grows in colonies in the ocean.
Coral polyps secrete a strong calcium structure that is used in jewelry making.
In jewelry making, coral is either carved into beads , cameos , or other forms, or is left in its natural branch-like form and just polished. It used to be thought that coral protected the wearer, so it was a traditional gift to children. Coral has a hardness of about 3.5 and a specific gravity of 2.6 to 2.7. Since it is composed of calcium carbonate, coral will effervesce if touched with acid. Imitation coral is made form glass, porcelain, or plastic.