Prices of rubies are primarily determined by color. The brightest and most valuable "red" called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. Cut and carat (weight) also determine the price.
The hardness (Mohs scale) : 9.0
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In the past, the pigeon-blood red color shade of ruby is the most beautiful and expensive. The sources of the most beautiful and expensive pigeon-blood ruby were in Thailand and Myanmar.
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