The specific gravity (SG) is the ratio of the mass of a material to the mass of the same volume of water. It is calculated by using electronic scales to accurately measure the weight of a stone both in air and in water. Every gem mineral has its own SG or characteristic SG range; that of diamond, for instance, is 3.52 and of corundum, 4.00. Specific gravity is a very helpful complementary property in gemstone identification.
