If you’re looking for a stone that’s beautiful, interesting, a bit different and still hard enough to wear in everyday jewellery, then look no further than the star sapphire.
Star sapphires are so-called because they exhibit an optical phenomenon called ‘asterism’, which looks like a 6-ray star on the surface of the stone. Whilst 12-ray stars do exist, it is much more common to see those with 6. Asterism is caused by two main factors: the first is due to the crystal structure of the sapphire, which is trigonal. Trigonal crystals will typically form with 6 faces. The second factor is due to many tiny, long inclusions inside the stone called ‘needles’ that run in three directions following the crystal structure of the stone, intersecting each other in the middle. When a light is pointed on the surface of the stone, it is reflected off these three-directional needles, causing the six ray star. Star sapphires are cut en cabochon in order to maximise this optical phenomenon.
Our head designer Alicja has a great analogy for describing asterism, which you can try yourself at home. Get a reel of thread and shine a light down on it. You will notice a sheen appear across the thread from the light. This is a cat’s eye (See our previous post on cat’s eye emeralds here https://www.holtsgems.com/blogs/explore/why-we-love-cats-eye-emeralds). Asterism is when you have three of these cat’s eyes intersecting each other at the middle to create a star. That’s a little more difficult to do with reels of thread but hopefully you get the idea!
Star sapphires come in a variety of colours, from blue to pink to grey. Quality factors include size and quality of the star. We have recently added some new stones to our stock, which are now available on our website.