Pearls come from a living sea creature. Most pearls come from oysters either freshwater or saltwater environments.
As oysters grow, an internal organ called the mantle uses minerals from the oyster's food to produce a substance called nacre. Nacre is the material that forms the oyster's shell. When a foreign substance, such as a grain of sand, may find its way into the oyster and get stuck between the mantle and the shell.
To protect itself, an oyster's natural reaction will be to cover up the irritant layer by layer of nacre. This substance, usually used to create the shell, will instead form a pearl.
"Sharing is caring", by Ivy Teong, Chief Designer, Juwelen Design. She is also the author for juwelendesign.blogspot.my or ivyteong.blogspot.com