description Star Sapphire Overview
Star sapphire is a variety of the mineral corundum that displays the optical phenomenon of asterism, typically forming a six-rayed star shape when viewed under direct light. This effect is caused by microscopic rutile needle inclusions, known as silk, within the stone. To best display the star effect, these gemstones are almost always cut en cabochon rather than faceted. One of the most famous examples is the 563-carat Star of India, a large blue star sapphire currently housed at the American Museum of Natural History in New York.
help Star Sapphire FAQ
What causes the star effect in a star sapphire?
Microscopic rutile needle inclusions, known as silk, reflect light into asterism. When cut and viewed in direct light, they can produce a characteristic six-rayed star.
Is a star sapphire a real sapphire?
Yes, star sapphire is a variety of corundum, the same mineral family as ordinary sapphire and ruby. Corundum has a Mohs hardness of 9, although the stone's inclusions and cut still affect durability and appearance.
How should a star sapphire be cut to show its star?
Star sapphires are usually cut as cabochons with a smoothly curved surface rather than faceted like a diamond. The curved cut helps the rutile silk display the six-ray asterism under a direct light source.
What is the difference between a star sapphire and a star ruby?
Both show asterism caused by aligned inclusions in corundum. A star ruby is red, while star sapphire can occur in blue, gray, yellow, pink, or other sapphire colors.
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