Specific Gravity (SG)
The densities of gem materials differ from one another. A gem’s specific gravity signifies the ratio of of it’s weight in comparison to that of an equal volume of water at 4 degrees centigrade. A higher ratio indicates a more dense and heavy matter. Using specific gravity, you differentiate the carat weights of gems that are the same size. Example – A 2.0 carat alexandrite (higher SG) would be the same size as a 1.4ct emerald (lower SG).