The term sapphire (without other adjectives) identifies the blue-azure variety of corundum, but the same name is frequently used, together with an adjective, to identify any color other than blue (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 grey harmophane and the colourless sapphire known as leucosapphire.
The typical blue-azure color of the gem comes from inclusions of hematite and rutile. If the inclusions are oriented in particular ways, the phenomenon of asterism can occur.
It can be found in nature in metamorphic rocks resulting from the remelting of a mica schist, a quartzite or a limestone, in magmas poor in silica and in their respective alluvial deposits. The latter are the main deposits exploited today. In this regard, the deposits in Australia, Sri Lanka, Burma and Thailand are worth mentioning. In Italy, small sapphire crystals are found in the calcite of Terminillo.
Sapphire can be produced synthetically with 5 types of synthesis. To distinguish natural sapphire from synthetic sapphire, a microscopic examination of internal inclusions and spectrometric and spectrophotometric analyses are performed.
The most common cut for this gem is the oval or round faceted one, but other types are not excluded, such as the heart or baguette. Among the known gems of exceptional size, it is worth mentioning the "Star of India", of 563 carats, preserved at the Museum of Natural History in New York.
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