Natural Star Sapphires
Star sapphire is sapphire (corundum, Al2O3) that shows asterism: a six-rayed star that glides across the surface of a cabochon under a single light. The star is created by fine needles of rutile or other minerals aligned in three directions in the crystal. With a Mohs hardness of 9, it is among the most durable star stones.
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Gemstone guide
Natural Star Sapphires
About star sapphire
Star sapphires occur in blue, grey, yellow, black and other colors. Black star sapphire, from Thailand and Australia, often shows a golden star on a near-black body, caused by needles of hematite and ilmenite. Sri Lanka is famous for blue star sapphires, including some of the largest ever found. Some star sapphires on the market have the star created or strengthened by diffusion treatment, which is always worth knowing.
What you'll find in this collection
Our star sapphires come from Thailand. You'll find oval and round cabochons from about half a carat to 2 carats, mostly black star sapphires and some blue. Most are untreated; diffusion-treated stones are marked as such on the listing.
How to recognise star sapphire
Look at the stone under a single point of light: a natural star moves as you tilt the cabochon and is often a little uneven, with rays that may be stronger on one side. Diffusion-treated stars are usually very sharp, look painted on the surface and sometimes show unusually even color. Natural black star sapphire often shows a golden sheen across the whole dome.
Caring for star sapphire
Star sapphire is hard and tough. Clean it with warm soapy water and a soft brush.
Every stone is natural, and each listing gives its weight, size, origin and treatment, with photos of the actual stone.