The diamond is most popular of all gemstones with it's characteristic and brilliance .
It is a hardest naturally occurring substance on Earth.

Diamonds are crystals of pure carbon that have been subjected to tremendous pressure and heat.
The diamond has the highest index of refraction: 2.419.
Hardness: Diamond is a perfect "10", defining the top of the hardness scale. Hardness C Isometric 10.0 (Mohs' scale)
Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other substance.
Thermal Conductivity: Diamond conducts heat better than anything does
Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)
Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance.
Color: Colorless to Various, Color, Transparent to sub-translucent

Diamonds come in a spectrum of colors from colorless to black; they may be transparent, translucent or opaque.
Gem diamonds are primarily transparent and colorless .
Blue and pink diamonds are the most valuable.
Red diamonds are very rare.
Clear white diamonds are called diamonds of the first water.

When found or mined, diamonds look like fragments of glass. Two or more gems are usually cut from a rough stone. Diamond gems have been cut in many different shapes. Most of the world's diamonds are mined in African countries. Zaire produces mostly industrial diamonds; South Africa is the major source of gem-quality diamonds. They are also found in India,Borneo, Brazil, Siberia ,Australia and U.S.

Because of its extreme hardness, the diamond also has important industrial applications.
Gem with poor quality because of color or faults, are used in industry.
Most industrial diamonds are gray or brown and are translucent or opaque.
Industrial diamonds are employed as gem cutter to shape and polish diamonds and other gems. Tiny holes drilled in diamonds are used to draw ductile metals like copper into extremely fine wire for the electronics industry. The stones are also used to true the surfaces of precision grinding wheels. In machine shops, tools tipped with diamonds perform precision-cutting tasks. Geologists and engineers use diamond-tipped hollow steel bits for drilling deep rock formation samples.