Gemology 101: Sapphire

Pope Innocent III may have once decreed that “…the ring of a Bishop should be made of pure gold and set with an un-engraved sapphire….”, but the beautiful gemstone isn’t just for the ecclesiastical.


What they are
Sapphire is a gemstone variety of the mineral corundum, a crystalline form of aluminium oxide. It is the trace amounts of other elements – like iron, titanium, chromium, copper and magnesium – that make a sapphire blue, yellow, purple, orange or green.

Sapphires have a trigonal crystalline structure with a Mohs hardness of 9 – making sapphire the second hardest gemstone after diamond.

How they’re made
Sapphires form in feldspathoid-bearing igneous rocks – a group of tectosilicate minerals – that have low silica content. They can also form in recrystallized limestone and metamorphic rocks which possess little silica and plenty of aluminum – including marbles and some mica schists.

Where they’re found
Sapphire and ruby, the other member of the corundum family, are mined throughout the world. Notable sapphires such as The Logan sapphire, the Star of India, and the Star of Bombay, all originate from Sri Lankan mines. As of 2007, Madagascar is the world leader in sapphire production. Prior to this, Australia was the largest producer of sapphires.


What to look out for
It is common practice to heat natural sapphires to enhance and improve their clarity and color. This is done by heating the gemstones for a few hours in furnaces to temperatures between 500 and 1800°C, or alternatively by heating them in a nitrogen-deficient atmosphere oven for several days. A heat-treated blue sapphire will become more blue in color and lose some of natural rutile inclusions, also known as silk.

Looking to own a dazzling sapphire? September’s birthstone just so happens to be the beautiful blue sapphire. You can personalize and purchase a range of blue sapphire jewelry at

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What is your favorite sapphire hue? Tell us below!

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