Ruby is the July birthstone and 15th and 40 anniversary stone. Finely colored rubies are one of the most expensive of all gems, with the exception of rare colored diamonds. Because natural flawless ruby is virtually unheard of, synthetics are usually easy to spot! In addition to synthetics, common ruby imitators are spinel, rubellite tourmalines and pyrope garnets. In addition, garnet may be misrepresented as Almandine ruby, Australian ruby, Bohemian ruby, and Cape ruby, while spinel may be called Balas ruby and Ruby spinel. Tourmaline may be referred to as Siberian ruby. It was not until 1800 that ruby was recognized as a separate mineral; prior to 1800 red spinel and red garnet were designated as ruby, from the Latin which means rubens red. Chromium is the coloring agent for ruby and the "pigeon's blood" is a desirable color, red with a overtone of blue.
Famous rubies are distinguished because of their size or extraordinary beauty, are located in various museums and private collections. For example, the 167-carat Edwardes Ruby, named in honor of Major-General Sir Herbert Benjamin Edwardes (1819-68) who served for the British in India, is located in the British Museum of Natural History. The Smithsonian has the 137-carat Rosser Reeves Ruby, a star ruby, while the American Museum of Natural History has the 100-carat Edith Haggin de Long Ruby. The famous Black Prince's Ruby and Timur Ruby, both part of the British Crown Jewels, are in fact red spinels. The Smithsonian has a most spectacular star ruby over 138 carats, the Rosser Reeves Ruby, as well as a recent acquisition of the largest faceted ruby in their collection.
Although gem treatment and enhancement probably go back several thousand years, modern methods for heat treating sapphire rough arrived by 1920, with ovens capable of reaching the necessary temperatures of over 1500° C. Virtually all rubies and sapphires sold today are heat treated for color and clarity enhancement, with the exception of stones mined prior to 1975, that have not been subsequently treated.
The best quality rubies comes from Mogok in Myanmar (Burma), India and Vietnam. In addition to the more famous US sapphire sites in Montana, another location is found in Minnesota, according to the web authors at the University of Minnesota, Duluth.
Colored stones, such as ruby and sapphire, lack a universally-accepted system of quality analysis needed to arrive at logical price structures. However natural Burmese stones in 1/2 to 1 carat sizes with slightly purplish red colour and good clarity range from $400 to $3200 per carat in today's market.