1. Gem refers to precious or semi precious stones that have been cut and polished.
2. Imitation jewelry refers to any small objects of personal adornment that do not incorporate natural or cultured pearls, precious or semi precious stones (natural, synthetic or reconstructed) nor precious metal or metal clad with precious metal (except as plating or as minor constituents).
3. Precious stones are defined as the most wanted and highest appreciated stones for jewelry making purpose. Good color, luster and clarity make a stone optically attractive, while certain hardness gives a stone the durability, which is required for use in jewelry making.
4. Semi-precious stones are the general name for all the crystallized minerals that are not precious stones.