There are numerous ways to describe the qualities of gemstones in jewelry. Here are a few:
Specific gravity is a measurement of density. As a point of reference, gemologists compare the density of a gemstone to the density of the same mass of water.
Just as it sounds, hardness describes how well a gem resists being scratched. Experts test this by trying to scratch one gem with another. They rank them on what's called the Mohs scale, invented by a German geologist, Mohs, in 1812. Diamonds, being very hard, are at the top of the scale.
Everyone agrees that the color of your gem is an important characteristic. The colors we see come from how a gem reflects light. The natural, clear color of a diamond comes from its purity and crystalline shape. Presence of other minerals in a diamond can give it unique color hues, such as yellow, pink, or black.