Mogok - The Valley of Rubies
"Long before the Buddha walked the earth, the northern part of Burma was said to be inhabited only by wild animals and birds of prey. One day the biggest and oldest eagle in creation flew over a valley. On a hillside shone an enormous morsel of fresh meat, bright red in color. The eagle attempted to pick it up, but its claws could not penetrate the blood-red substance. Try as he may, he could not grasp it. After many attempts, at last he understood. It was not a piece of meat, but a sacred and peerless stone, made from the fire and blood of the earth itself. The stone was the first ruby on earth and the valley was Mogok".
Burma has long been associated with the most desirable rubies in the world. Within Burma (Myanmar), the most famed region is the Mogok Valley, or Mogok Stone Tract, in the Pyin Oo Lwin district, north-east of Mandalay: a small area of a dozen square miles, of which only a portion is gem-bearing. Meanwhile, there are a few more small deposits to the North of Mogok, such as Namya, that produce rubies with similar characteristics. Although it is uncertain when mining first began, accounts indicate that rubies have been sourced in the Mogok area for well over a thousand years.
The earliest surviving records of mining activity began in 1597, when the King of Burma took over the mines. Burmese rubies, especially the ones from Mogok, have since sustained the longest renown.
Mogok-type rubies typically possess a red body colour and red UV-fluorescence. In addition, they may contain tiny amounts of light scattering rutile silk and a swirl-like growth pattern. It is this combination of features which give these rubies their characteristic appearance.
The ruby can command the highest prices of any coloured gemstone. Per carat prices of top-quality rubies have been rising, and broken numerous auction results. When appraising rubies, four factors come into play - Colour, Clarity, Cut, Size and Weight.
Colour is of utmost importance in determining a ruby's value. A saturated, pure, vibrant red to slightly purplish red colour is always desired. Orangey or purplish hues would rank lower on the quality scale. With certain stones that have a lighter pinkish hue, the stone would be called a pink sapphire instead. "Pigeon's Blood" is a term conferred on stones that display the finest examples of colour (slightly purplish to pinkish red, with a soft, glowing red fluorescence).
A natural, untreated ruby will almost always have some form of inclusion. Overtly conspicuous inclusions that lower a ruby's transparency, brightness or durability will always have a detrimental effect on its value. Intersecting rutile silk can sometimes cause asterism, a star effect on the surface of the ruby when it is cut into a cabochon, lending a unique beauty and increased value to the stone, when the star is of perfect symmetry, with good length (reaching the edge of the gem) and a sharp visible lines for each star.
Rubies are commonly fashioned into ovals and cushions, as these are most suitable to its natural crystal shape. Other shapes such as round, triangular, emerald-cut, pear and marquise rubies can also be found, though these would be hard to come by in larger sizes and higher qualities. The appearance of red to purplish red in one crystal direction and orangey red in the other is called Pleochroism and would be one of the considerations made during the cutting process. The cutter would always try to minimise the orangey colour by orienting the table facet to achieve a more even reddish purplish tone, but rarely at the expense of stone weight loss.
Fine rubies larger than one carat are very rare, and the price per carat increases exponentially for large size stones. Due to the higher density of rubies, a 1 carat ruby will always look smaller than a 1 carat diamond.
Information Face Sheet on Mogok Ruby, Gubelin