Sapphires and rubies are both members of the corundum family with the same hexagonal crystallographic structure. The basic chemical formula is AL22O3 .. the same for both ruby and sapphire. It is the presence of trace elements like chromium, iron, vanadium and titanium which are responsible for the wide range of colors in which the mineral occurs. When a corundum is red, it is known as a ruby and any other color is a sapphire. In practice however, the determination is not always so straightforward because there are no internationally accepted standards for the color of a ruby. Gemologists could describe the same stone as a purplish red ruby or a purplish red sapphire and borderline cases are not uncommon.
Sapphires are noted for the large range of colors in which they occur. The name fancy sapphire, is used to describe sapphires which are not blue. Fancy sapphires are available in an amazing range of colors including yellow, green, violet, pink, brown, purple, violet, white, black and orange.
Occurrences: The most notable deposits of Sapphire are located in Burma, Australia, East Africa, Sri Lanka, and Madagascar. Other well known deposits include Montana, USA; and Kashmir, India. The deposit in Kashmir is no longer producing and the deposits in Montana may not produce enough to be commercially viable.
The Source: Many of the important sapphire deposits in Sri Lanka, Madagascar, Kenya and Tanzania are geologically related to each other. Australia, Antarctica, Sri Lanka, Madagascar and Africa were all connected in a super continent known as Pangaea billions of years ago. Giant rivers carried gemstones from the same source and deposited them throughout this super continent as alluvial gravels. Between 200 to 400 million years ago, the continents began to separate as a result of tectonic forces and continental drift.
The same stones from the original deposit are now found in Sri Lanka, Madagascar, and Tanzania. Sri Lanka was probably closest to the source and we know this because the stones there are larger with better crystallization. As the stones were carried to what is now Madagascar and Tanzania, they would have became smaller and more rounded because of the longer distance they traveled. The largest stones are in Sri Lanka. South Madagascar and Tunduru, rough is generally smaller with less defined crystallization. The concentrations and colors of the gravels show remarkable similarity across this huge deposit.
The stones from these localities are extremely difficult or impossible to differentiate. To further complicate the geology, indigenous sapphires with more localized source rocks are also found in nearby areas.
Sri Lanka: is well known for the fine quality and broad range of colors of the sapphires which are found there. Almost every color is found. Ratanapura is an important center for mining and new stones are offered on the local market every day. Sri Lanka is known for producing the largest sapphires in the world.
Madagascar: sapphires are found at numerous locations throughout the country. The southern deposits in Illakaka are geologically related to the sapphire deposits in Sri Lanka, East Africa and Tanzania. The northern star sapphire and the north central ruby deposits are unrelated. The color of many of the stones is outstanding. Madagascar is politically unstable and relatively undeveloped with few roads and few people to discover new deposits. Madagascar should continue to be an exciting and important source for fine sapphires and other gems.
Kenya and Tanzania: The most important deposits are the Umba region in Kenya, and the Tunduru and Songea deposits in Tanzania. The deposits in Tunduru are related to the original super continent source rock. The Umba deposit shows many similarities and may also be related. Another important deposit in Songea, produces green, color change, and red sapphires (rubies). The Songea deposit is geologically unrelated to the other deposits.
The traditional heating of rubies and sapphires is a widely used and accepted enhancement process which can improve the transparency and/or the color of the stones. Techniques range from simply throwing gems in a fire to be cooked or burned to employing sophisticated electric or gas furnaces at specific pressures and atmospheric conditions. The treatment is permanent and heated stones do not require special care.
New treatments which are used to produce orange and yellow stones are more controversial The color is achieved through a process which includes the addition of foreign elements to achieve the desired color alteration. The treatment is a heat/diffusion process which may or may not completely penetrate the stone.
Sapphire has long symbolized truth, sincerity, and faithfulness. Tradition holds that Moses was given the ten commandments on tablets of sapphire, making it the most sacred gemstone. Because sapphires represent divine favor, they were the gemstone of choice for kings and high priests. The British Crown Jewels are full of large blue sapphires, the symbol of pure and wise rulers. Since sapphire symbolizes sincerity and faithfulness, it is an excellent choice for an engagement ring. When Prince Charles chose a sapphire engagement ring for Princess Diana, couples all over the world were inspired to revive this venerable tradition.