Artificial and imitation gems are of various kinds . Synthetic stones are made in the laboratory of the same chemical elements as natural stones . Among the synthetic gems produced commercially are rubies , sapphires , diamonds , emeralds , and spinel ' s .
Imitation pearls are glass or plastic beads coated with a preparation made from fish scales . A cultured pearl is made by inserting a small bead inside the oyster ; the irritation causes the oyster to deposit pearly material upon the bead , leading to the formation of a pearl .