Ruby is  the pink to red variety of Corundum and is classified as a precious gemstone. Ruby has a hardness of 9 on the Mohs scale and there are only two other gemstones that are harder, being Moissanite and Diamond. Ruby crystalizes in the most stable form of Aluminum Oxide with ions from Aluminum joining a bond with neighboring oxygen ions to form a perfect octahedral bond. When ~ 1% of the aluminum ions are replaced by trace amounts of Chromium, the absorption rate in the ultraviolet and yellow-green color spectrums are altered, producing the appearance of the pink to red color of Ruby. The change in absorption rate also creates a natural fluorescence which enhances the color and luster of the natural gem.

Rubies always have imperfections and inclusions. Often tiny rutile inclusions create a silk-like luster that can have a velvety or cloudy appearance. Just like Sapphire, Rubies also can exhibit asterism, when patterns of overlapping rutile inclusions disperse the light into three or six-pointed star reflection after cutting into cabochon. There is a minimum color saturation in the red spectrum required for Corundum to be classified as Ruby instead of Pink Sapphire. This distinction is not always clear and can lead to confusion.

High quality Ruby gemstones are mined in Thailand, Cambodia, Afghanistan, Brazil, Colombia, India, Madagascar, Pakistan and Tanzania. Before other important deposits were found, the Mogok valley of Myanmar was the world’s primary source for Ruby rough. Ruby, like other top gemstones, are evaluated using the four C’s of color, clarity, and carat weight. With Ruby color takes primary importance. A highly saturated rich red color with secondary pink to purple hues is the most valuable of colors.