Say the word Sapphire, and most people immediately picture a brilliant blue gemstone.
But Sapphire has a surprise.
It can occur naturally in almost every colour of the rainbow.
Pink, yellow, green, orange, purple, colourless—and even stones displaying more than one colour can all belong to the Sapphire family. In fact, the only colour of corundum that isn't called Sapphire is red. Red corundum has another very famous name: Ruby.
Sapphire has been treasured for centuries, but there's much more to this remarkable stone than beautiful jewellery. Its incredible hardness, unusual colours, geological origins, and connection to Ruby make it one of the most fascinating gemstones in the mineral world.
And because Sapphire is September's birthstone, there's no better time to take a closer look.
What Exactly Is Sapphire?
Sapphire is the gem-quality variety of a mineral called Corundum.
Pure Corundum is composed primarily of aluminum and oxygen and is naturally colourless. The spectacular colours we associate with Sapphire appear when tiny amounts of other elements become incorporated into the crystal while it's forming.
These trace elements can dramatically change the colour of the finished gemstone.
For example, the classic blue colour of Sapphire is generally associated with trace amounts of iron and titanium within the crystal structure.
Other combinations of trace elements can produce entirely different colours.
That means a deep blue Sapphire and a delicate pink Sapphire may look completely different while still being varieties of the same mineral.
Sapphire Isn't Always Blue
Blue is certainly Sapphire's most famous colour, but non-blue Sapphires are collectively known as fancy Sapphires.
They can occur in shades of:
- Pink
- Yellow
- Orange
- Green
- Purple
- Colourless
- Multiple colours within one stone
One particularly prized variety is Padparadscha Sapphire, known for its distinctive mixture of pink and orange tones.
There are also parti-coloured Sapphires, where two or more colours can appear within a single crystal.
This incredible range makes Sapphire much more diverse than many people realize.
Sapphire and Ruby Are Closely Related
Here's one of our favourite mineral facts:
Ruby and Sapphire are both Corundum.
Their names change because of colour.
When Corundum develops the appropriate red colour, largely due to chromium, it's classified as Ruby.
Gem-quality Corundum of other colours is generally classified as Sapphire.
So despite looking completely different in a jewellery case, Ruby and Sapphire are essentially geological siblings.
They share the same basic mineral structure, the same crystal system, and even the same exceptional hardness.
One of Nature's Hardest Minerals
Sapphire ranks 9 on the Mohs Hardness Scale.
Only Diamond, at 10, ranks higher on the traditional scale.
That exceptional hardness is one reason Sapphire has been so highly valued for jewellery. It resists scratching much better than many other gemstones, making it particularly well suited to pieces that may be worn regularly.
But Corundum's hardness also makes it valuable outside the gemstone world.
Synthetic Sapphire and Corundum are used in a variety of industrial and technological applications where strong, scratch-resistant materials are needed.
It's a beautiful example of a mineral that's fascinating both scientifically and aesthetically.
How Does Sapphire Form?
Sapphire forms under specific geological conditions where aluminum is available but silica is limited.
It can develop within certain igneous and metamorphic rocks, often deep within Earth's crust under significant heat and pressure.
Over immense periods of time, geological processes can expose these deposits at the surface.
Weathering may then release durable Sapphire crystals from the surrounding rock. Because Corundum is so hard and resistant, those crystals can survive erosion and eventually become concentrated in river gravels and other sedimentary deposits.
Some Sapphires are therefore recovered not from the rock where they originally formed, but from sediments where nature has gradually transported and deposited them.