What is a Gems?= Some gems-like pearls, amber, coral, and ivory- are organic. This means they come from plants or animals. But most gems are minerals: natural, inorganic materials with specific chemical compositions. Most have a characteristic structure, too. 

To be a gem, a substance must share three important traits with all other gems: beauty, rarity, and durability. Each trait, however, represents a range, so all gems can possess different levels of all three traits.