In terms of price per carat, a good ruby is second only to the rarest diamonds in value. Chemically identical to sapphires, rubies belong to the corundum family of minerals, but owe their distinctive shade of vivid red to chromium impurities. Rubies are another extremely historic stone, and have been treasured for millennia, particularly in India where they were known as the 'king of gems'. For all their prominence however, rubies of good colour and clarity in sizes over a carat are exceptionally rare, and good examples can command extremely high prices at auction. Traditionally, rubies from Burma are the most valued, particularly those fabled stones showing a rich, pure red with the slightest hint of blue, known as 'Pigeon's Blood'. In addition to the historical Burmese sources, rubies from Thailand, Cambodia and Vietnam are also highly regarded, as are newer sources, such as Mozambique. Like sapphire, ruby is often heat treated to improve its colour, meaning that high quality, untreated specimens are highly sought after. The birthstone for the warm summer month of july, the word 'ruby' comes from the latin 'ruber', meaning red, and it is this colour that has led to their association with love and romance, as well as warmth, energy and vitality. Like all corundum, ruby is a 9 on the Moh's scale of hardness, meaning that in addition to its beauty, it is a very hard-wearing stone, perfectly suitable for everyday wear.