The term GEM OF AN OYSTER is a crossword solution for the word PEARL. A PEARL is a hard, round object that forms inside the shell of certain mollusks, such as oysters. It is often used in jewelry and is considered a valuable gemstone. Pearls are created when an irritant, such as a grain of sand, enters the mollusk's shell and the mollusk secretes a substance to coat the irritant. Over time, this substance builds up and forms a PEARL.