Congratulations to all of you celebrating a 5th anniversary, the anniversary of sapphire! Symbolising love and fidelity, sapphire is a beautiful gemstone that’s tough enough to withstand a few knocks – just like a good marriage.
Though blue is the most popular and well-known colour, sapphires occur in a wide range of pretty hues: blue, pink, green, yellow, orange, purple, black and even colourless. There’s no such thing as a red sapphire though. Know why? It’s because a red sapphire is known as a ruby. Sapphire and ruby are both varieties of the mineral corundum, and the variation in colour is caused by different chemical elements within the gemstones’ structure.
I’ve come across some phenomenal sapphires on my travels, and I don’t just mean that they made my jaw drop! The term ‘phenomenal’ in gemmology refers to gemstones that have fascinating optical properties.
The most well-known type of phenomenal sapphire is probably the star sapphire. Star sapphires exhibit a property called ‘astersim’, which means that they seem to have a star shape floating across their surface. Asterism happens when light bounces off dense, linear inclusions of titanium dioxide (also known as ‘rutile’ or ‘silk’) in the gemstone’s body. In black star sapphires, the rutile is hematite and some Thai sapphires contain both titanium dioxide and hematite. As well as causing the floating star effect, the rutile gives the star sapphire its milky, opaque appearance. Depending on the nature of the rutile, a sapphire may exhibit a four, six or twelve-rayed star.
You probably know that alexandrite is a colour change gemstone, but did you know that it’s possible to buy a colour change sapphire? Colour change gemstones appear to be different colours in natural and artificial light because the gemstone’s chemical makeup means that particular ranges of wavelength (i.e. colours) in the light spectrum are absorbed more intensely under one light source than another. The colour change in sapphires is most commonly a subtle but pretty change from blue to violet.
Bi-coloured or ‘parti’ sapphire displays two different colours (usually blue and greenish yellow) within the gemstone no matter what the light source. Though found in Tanzania, Madagascar and Nigeria, the world’s main source of parti sapphire is Australia. I was lucky enough to find a few myself, when fossicking in the outback on my travels down under. These intriguing and unusual sapphires certainly make for a striking piece of jewellery!
Happy 5th anniversary! Let’s not forget that sapphire is also September’s birthstone!
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