Gemstones Gemstones can be naturally mined, laboratory-created or imitation. Stones created in a lab look identical to stones mined from the earth. The big difference is in the cost – laboratory-created stones are less expensive than naturally mined stones. But because they look just like stones mined from the earth, they must be identified as lab-created. Imitation stones resemble naturally mined stones but are not identical and are usually made of glass or plastic. Imitation stones must be identified as imitation. If you are purchasing a naturally mined stone, ask if it has been treated. Gemstone treatments – such as heating, dyeing or bleaching – can improve a stone’s appearance or durability. Some treatments are permanent; some may create special care requirements. Treatments also may affect the stone’s value.