Ruby is the birthstone for July and one of the most valuable gems. The red of ruby is the color of love and passion. The finest color of the birthstone is a deep red with a hint of purple, called “pigeon’s blood”. A variety of the mineral corundum, ruby gets its color from trace amounts of the element chromium.
Ruby has a hardness of 9 which is second in hardness to diamond and very durable.
Rubies are often heat treated to remove purplish coloration, leaving a purer red. The process can also remove “silk” (minute needle-like inclusions) that can cause a gem to appear lighter in tone and be more opaque. Heat treatment is stable to normal conditions of wear and care.
Large, gem-quality rubies are rare and can be more valuable than comparably sized diamonds. Ruby can command the highest prices of any colored gemstone.
Rubies as well as sapphires can display asterism, the “star effect,” due to rutile inclusions in their hexagonal crystal matrix. If this rutile is sufficiently abundant and precisely arranged, proper cabochon cutting can create star rubies.