Ruby belongs to the corundum gem family and has a purple-bluish red to a yellow-red color. They tend to have uneven colors and normally have minor inclusions, such as minerals, growth structures, canals and cavities. It's easy to identify the origins of a ruby (i.e., country and area) based on the type of inclusions that are found in the stone. They also tend to be cut in the country where they originated from.
A pure ruby such as the Burmese "pigeon's blood" ruby has a red color with a hint of blue. They are very expensive and are highly sought after.
Rubies that are produced in Vietnam or Tanzania are similar in color to the Burmese rubies but the Tanzanian rubies are somewhat opaque. Sri Lankan rubies tend to be light red to raspberry red in color. Thai rubies are similar in color to garnet and are produced more than Burmese rubies. Thai rubies have a slightly darker purplish red color, less rutile needle inclusions, and more luster than Burmese rubies.
Rubies also exhibit strong pleochroism which shows yellow-red and deep carmine red when viewed at different angles. Pleochroism dictates the orientation of the material and the cutting style used for the ruby. Depending on the orientation of the ruby and how the light hits the stone at different angles will help to determine which cut will help to accentuate the red color of the ruby.
When examining rubies under different lighting conditions the ruby will have a varied intensity in its color. Under indoor lighting, the ruby's color appears intense and 'hot' while in daylight, the color appears cooler. In order to distinguish synthetic rubies from real rubies a useful indicator is the fluorescence of the stone. Synthetic rubies tend to have a very strong fluorescence.
Hardness: 9 Mohs
Specific Gravity: 3.97-4.05
Refractive Index: 1.762-1.778
Crystal Form: Trigonal, hexagonal prisms, tables and rhombohedrons.