Ruby - Sapphires coloured by chrome, are called 'rubies' - the king of the gemstones In the fascinating world of gemstones, the ruby is the undisputed ruler. For thousands of years, the ruby has been the most valuable gemstones on Earth. It has everything a precious stone should have: magnificent colour, excellent hardness and outstanding brilliance.
Top-quality Rubies are extremely rare. Beauty, magnificent colour, transparency, and durability are the main features. Color determines the value of a Ruby. Highly saturated medium or dark medium tones are best. Sri Lanka : is well known for the finest quality sapphires, and the largest sapphires in the world. See list of World Famous Gems.
Rubies and sapphires are both members of the corundum family with the same hexagonal crystallographic structure. The basic chemical formula is AL 2 O 3 .. the same for both ruby and sapphire. It is the presence of chromium, iron, vanadium and titanium which are responsible for the wide range of colors in which the mineral occurs. The red color in rubies is primarily a result of the presence of chromium. A red corundum is known as ruby and any other color is called a sapphire.
The heating of rubies and sapphires is a widely used and accepted enhancement process which can improve the transparency and/or the color of the stones. The treatment is permanent and heated stones do not require special care. 
