Specific Gravity (Density)
ensity, or Specific Gravity, is a bulk property of a material. Specific Gravity is the ratio expressing the weight of a mineral compared to that of an equal volume of water at 4° C. So, a specific gravity of 3 means that, at 4° C, one cubic centimeter of the material weighs 3 times as much as one cubic centimeter of water.
Density is a useful measurement in gem identification. However, the density of a particular mineral may vary greatly, even within a single crystal, due to the presence of impurities, cracks or bubbles. The density of a mineral can be affected by several factors, including chemical composition and crystal structure. For example, Diamond and graphite are both crystalline forms of the element carbon. Diamond has a density of 3.5 because the carbon atoms are tightly packed together in the structure.