There are three types of gemstones:
Natural gemstones include minerals and organic materials such as amber, sapphires, coral, fossil, ivory, emeralds, rubies, cultured freshwater pearls and natural salt water pearls.
Synthetic and Simulant are terms used by the USBM for laboratory grown gemstones. Other terms are sometimes used to refer to laboratory grown gemstones. Synthetic gemstones have the same appearance, physical, and chemical composition, crystal structure as the natural material that they represent, however they have no effect when used for gem therapy. The synthetic process attempts to simulate the conditions that occur when natural gemstones are formed within the Earth.
Not all synthetics are simulants, and not all simulants are synthetic. A gem simulant is a stone, which appears similar or identical to another stone, so that cubic zirconia and natural colorless sapphire can both be used to simulate a diamond. A synthetically produced diamond is a real diamond.
A gemstone must possess a certain number of attributes for it to be desirable. Those attributes are Beauty, Durability, Rarity, Color, Fashion, and Special Properties. However, a gemstone's desirability is ultimately decided by the individual's taste.
Majority of gemstones are minerals, however there is a small group of gems that are organic, meaning they are formed as either a product or a part of a living organism, e.g., pearls are formed within a mollusk, such as an oyster, that deposits a substance called nacre around an irritant that entered the organism.