When buying a sapphire, including the rainbow combination, ask if the stone has been treated in any way. Some common treatments to enhance gems include irradiation, heat treatment, dyeing and coating. Not all of these treatments will devalue the stone, but always ask so you know what you're getting.
Sapphires can be heated at high temperatures to give them a better color and clarity. It is estimated that 90 percent of the Sapphires on the market have undergone some sort of treatment, which does not affect the value of the stone. However, untreated sapphires do command a higher price.
Sapphires are mined all over the world, including several locations in the United States and the location where the sapphires are mined can have a great effect on the price. All sapphires have a hardness of 9 on the Mohs scale and are considered very durable to be worn everyday.
Traditionally the sapphire is believed to bring clarity of mind and disintegrates disharmony with healing properties for rheumatism, colic, and mental illness.
*Resources by ebay review and rainbow sapphires.