Color: Varying red
Hardness: 9 Mohs
Specific Gravity: 3.97 - 4.05
Refractive Index: 1.766 - 1.774
Ruby is named because of its red color. The red color varies with the individual deposits, so it is not possible to determine the source area from the color, as each deposit yields various tones.
The designation "Burma-ruby" or "Siam-ruby" is erroneous, and refers more to quality than origin. The most desirable color is "pigeon's blood", pure red with a hint of blue.
All natural rubies have imperfections in them, including color impurities and inclusions of needles known as 'silk'. We use these needle inclusions in rubies to distinguish them from synthetics. It is extremely common and acceptable now that almost all rubies are treated in some form, with heat treatment being the most common practice.