Density and specific gravity


Specific Gravity or Density
In general, The specific gravity of a gem is its weight when compared with the same volume of water at a temperature of 4 degrees Celsius. The denser the minerals in the gemstone are, the heavier the weight or specific gravity will be. Heavier gemstones are usually harder as well. This term, is now replaced by density, which is expressed typically as grams per cubic centimeter (g/cm­­3)

Weight in fact is not constant  attribute. It depends on the magnitude of the gravity at the respective location where it is measured. But for the determination of the weight of gemstones,this does not matter, since the measurement is always done under the same gravitation condition.

The density of gemstones varies between 1 and 8. Values under 2 are considered light,  those from 2 to 4 normal and those over 4 are considered heavy. The valuable gemstones (such as diamond, ruby and sapphaire) have densities that are much greater than the common rock forming minerals, especially quartz and feldspar.

The range is from amber, which has a specific gravity of 1.08 and opal, with a specific gravity of 2.05, all the way up to corundum (sapphires and rubies) with a specific gravity of 3.99, spessartite garnet, specific gravity of 4.15, marcasite, specific gravity of 4.9, and cuprite (s.g., 6.0) and casseterite (s.g., 6.9). Diamond is in the heavy mid-range, with a specific gravity of 3.52.