September's Birthstone, Sapphire

Sapphire, September's birthstone,  is a form of the mineral corundum, a normally drab grey mineral. Red corundum is called the ruby, while all other gem quality forms of corundum are called sapphires.

Typically, sapphires appear as blue stones, ranging from very pale blue to deep indigo, due to the presence of small amounts of titanium and iron within the crystal structure. The most valued shades of blue range from the medium-deep cornflower blue to medium dark blue, or slightly violetish blue.

Sapphires also occur in other natural colors and tints – colorless, gray, yellow, pale pink, orange, green, violet and brown – called fancy sapphires. These different colors are caused by different kinds of impurities within the crystal. For example, yellow sapphires get their color from ferric iron, and colorless gems have no contaminants.

The biggest source of sapphires world-wide is Australia, especially New South Wales and Queensland.   Australian sapphires typically are blue stones with a dark and inky appearance.   In India, Kashmir used to be a well-known source of the cornflower-blue stones. In the United States, a major source is the Yogo Gulch Mine in Montana that mostly yields small stones for industrial use.

Sapphires are commonly heated to improve their color and reduce cloudiness that is caused by inclusions. The inclusions are responsible for the "star" or "cat's eye" in star sapphires. 

One of the most famous sapphires rests on the Imperial State Crown, worn by Queen Victoria in 1838. It resides in the British Crown Jewels in the Tower of London. This gem is called the St. Edward’s Sapphire because it once belonged to Edward the Confessor, who wore the stone on a ring during his coronation in 1042.

(Parts of this post are being shared from the website Earthsky.org)