The term sapphire (without other adjectives) identifies the blue-blue variety of corundum, but the same name is frequently used, together with an adjective, to identify any color other than the blue one (for example the ruby variety).
Colored corundums were once named after other stones, followed by the suffix "oriental" (for example, the terms oriental amethyst and oriental emerald are today identified with the names purple sapphire and green sapphire).
Other varieties are the orange one, called padparadscha, the most precious variety of corundum, the dull gray armophane and the colorless sapphire known as leucosaphire.
The typical light blue color of the gem comes from inclusions of hematite and rutile. If the inclusions are oriented in particular ways, the phenomenon of asterism may occur.
It can be found in nature in metamorphic rocks deriving from the remelting of mica schist, quartzite or limestone, in silica-poor magmas and in their respective alluvial deposits. The latter are the main deposits exploited today. Mention should be made of the Australian, Sri Lanka, Burma and Thailand deposits. In Italy small sapphire crystals are found in Terminillo calcite.
Sapphire can be produced synthetically with 5 types of synthesis. To distinguish natural sapphire from synthetic sapphire, a microscopic examination of the internal inclusions and spectrometric and spectrophotometric analyzes are carried out.
The most common cut for this gem is the oval or round faceted cut, but other types are not excluded, such as the heart or baguette cut. Among the known gems of exceptional size, the 563-carat "Star of India", preserved at the Natural History Museum in New York, should be mentioned.
