Sapphire, the birthstone for September, is a gemstone variety of the mineral corundum. Most well known for its intense blue colour, it is actually found in a variety of colours due to trace amounts of different metals.
The stone is a popular choice for jewelry, and not just because of it's colour - it's also one of the world's most durable stones, falling just below diamond and moissanite.
Sapphire is typically blue, ranging from a greenish to violet hue, but it can be found naturally in yellow, purple and orange too. These 'fancy sapphires' sometimes exhibit colour changing properties similar to alexandrite, veering from blue in daylight to purple in incandescent light. The name 'sapphire' normally applies to any corundum that is not red (and therefore a ruby).
Sapphire is a remarkably tough gemstone, measuring 9 on the Moh's scale. This is what makes it a great choice for jewelry and explains why it's even used in electrical components, scientific instruments and shatter-resistant windows.
Australia, Thailand, Sri Lanka and China are seen as the largest sources of sapphire, but it is also found in North America, mostly in Montana.
Sapphire has symbolized nobility and romance for centuries.
In Ancient Greece and Rome, kings and queens believed it protected them from envy and harm. During the Middle Ages blue sapphires were worn by the clergy, and they were said to attract heavenly blessings.
In 1902, French chemist Auguste Verneuil developed a process for making synthetic sapphire.
Colour is the most important factor in the valuation of sapphire, with a strong blue or violet-blue colour fetching the highest prices. The most valuable stones will have strong saturation without a darkened colour or compromised brightness.
Clarity also plays a role in the gemstone's value. Most sapphires have some inclusions, but if they are seen to affect the stone's durability they will impact on its value. Perfectly clear sapphires are extremely rare.
Sapphire is often treated to enhance its colour and clarity, mainly by heating the stone in a furnace for several hours which improves its blue colour and reduces inclusions.
Untreated sapphires are rarely found on the market - in fact, it is estimated that at least 95% of stones are heat-treated.
It is easy to see why sapphire is such a popular choice for jewelry. The stone's deep blue shade gives it a romantic mystique, and its durability means it can withstand everyday use.
Sapphire is more versatile in colour than many people know, and that's why jewellers often refer to the blue variety as 'blue sapphire'.