Gems are also called as precious or semi-precious stone that is cut, polished and resized to make use by jewelers for ornaments or other purpose. It is a naturally occurred beneath the earth with unique attraction, chemical composition, crystal system and durability. Most of the gems are hard, but some stones are soft and tough. Usually, it is made of minerals that encompass high degree of beauty, rarity, durability and desirability. A gemstone is highly graded for its beauty and appearance. Properties that determine the value and beauty of a stone are color, clarity, cut, carat and rarity. Gems are available in different shapes, sizes, cut, color and clarity. Gemstones has unique characteristic that is classified by gemologist in different specifications. Traditionally, gems are classified in different method, but today gems are classified by gemologist by the technical terminology specified to the field of gemology.

Traditionally, gemstones are classified as precious and semi precious gemstones. Diamond, ruby, sapphire and emerald are precious stones and others are semi precious. Today, huge number of stones are available and they are identified by gemologist by their characteristics. In modern times, gemologists identify gemstones by their characteristics and the technical terminology specified for the gem. Physical characteristic that makes a gem valuable are color, clarity, cut, unusual optical phenomena.

Gemologists characterize gemstones in different terminology. Firstly, chemical composition of the stone is identified i.e. diamond - C and Amethyst - SiO2. Secondly, the crystal properties are ascertained using the crystal system. Some of the crystal system that describes crystal properties is cubic, trigonal, monoclinic, hexagonal and orthorhombic.

Optical characteristic of gemstone are considered. The optical characteristic is primarily derived from chemical composition and crystal structure. Color, optic character, refractive index, birefringence, dispersion, fluorescence, phosphorescence and clarity are some of the optical characteristic of the stone.

Next, gemstones are characterized by the feature called specific gravity. Generally, gemstones adversely differ in their density. Gemologist refers to specific gravity or relative density, the ratio of density of the gemstone.

Durability, the hardness and toughness of the stone. Lastly, gemstones are characterized by their durability. Durability refers to hardness and toughness which in-turn refers to resistance to scratches or piercing and resistance to breakage. Diamond is the hardest and toughest gemstone that is resistant to scratches and breakage.

Also, it is characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster.

Stones are classified into different groups, varieties and species. For instance, ruby is a variety of red and corundum species. While emerald, aquamarine, morganite comes in the species beryl.

Even gemstones are classified as natural or synthetic. Synthetic are created in laboratories under specific conditions, while natural will have imperfections due to the uncontrolled growth condition in nature.