What is a gemstone ? What does gemmy mean ?

Gemstone : definition

A gem (or a gemstone) is a cut stone which presents certain qualities of hardness, clarity, resistance, brilliance, color, rarity, which are worth to him an appreciated use in jewelry. The name of "precious stone" was officially repealed by French legislation in January 2002. It is a historical name which applied in France to the four gems which are the diamond, the sapphire, the ruby and the emerald. The other cut minerals being qualified as fine stones.

In mineralogy, the adjective "gemmy" is used to qualify the transparent quality of a crystal. For example, a "gemmy" sapphire crystal is a crystal transparent enough to be cut into a gemstone.