Properties of Natural Gemstones

Color

• The color of a gemstones depends on how light passes through it. Diamonds create a rainbow of colors because they split the light. Other gemstones appear a certain color because they absorb the wavelengths of lights entering them. Also, the presence and amount of an element in a gem can affect its color and the strength of that color. For example, the chemical compositions of rubies and sapphires make them different colors. The sapphire and ruby contain corundum and have close chemical compositions. However, the chromium in the ruby makes it red, and the iron and titanium in the sapphire make it blue.

Chemical Composition

• Each gemstone has its own chemical composition. This is one way we can distinguish between them. For example, the emerald is a beryllium aluminum silicate, and a diamond is made up of carbon.

Crystal System

• Crystal systems of different gemstones are distinguished by the gemstone's crystallographic axes. The crystallographic axes are imaginary lines drawn between the points, joints or planes of crystals. These lines intersect in certain ways at the crystal's origin, which is a point within the crystal. The seven types of crystal systems are cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic. Like the chemical composition of a gemstone, the gem's crystal structure also contributes to a mineral's properties. The crystal system also influences what happens to light when it enters a mineral and where there are planes of weakness.

Hardness

• The hardness of a gemstone is the measure of that gem's resistance to abrasion. The hardness of a gemstone is measured using the Mohs scale, which compares all minerals to 10 different minerals. Minerals with a higher number on the scale will scratch minerals with a lower number. The intervals between minerals on the scale are not uniform.

Specific Gravity

• According to Glencoe Online, the specific gravity of a gem is the number of times heavier a gemstone of any volume is than an equal volume of water. In other words, specific gravity is the ratio of the gemstone's density to the density of water.