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Natural Star Rubies
Star ruby is ruby (corundum, Al2O3) that shows asterism: a six-rayed star of light that glides across the surface of a cabochon as it moves under a single light source. The star comes from fine needles of rutile, called silk, aligned in three directions inside the crystal. With a Mohs hardness of 9, star ruby is as durable as any ruby.
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Gemstone guide
Natural Star Rubies
About star ruby
Asterism is rare in ruby because the needles have to be dense enough to reflect light yet not so dense that they hide the color. A cabochon has to be cut with its dome centered on the crystal's main axis, or the star will sit off-center. Sri Lanka, Myanmar, India and East Africa are known sources. Star rubies are usually left unheated, because heating dissolves the silk that creates the star.
What you'll find in this collection
This collection holds natural star rubies, such as untreated oval cabochons from India of a few carats, each photographed under a single light to show its star.
How to recognise star ruby
Under a single point of light, such as a phone flashlight or the sun, a natural star ruby shows six rays that move as you tilt the stone; under diffuse light the star fades. Natural stars are often slightly uneven or wavy, while synthetic and diffusion-treated stars tend to look perfectly sharp and sit on the surface.
Caring for star ruby
Star ruby is hard and tough. Clean it with warm soapy water and a soft brush, and avoid ultrasonic cleaning if the stone has visible fractures.
Every stone is natural, and each listing gives its weight, size, origin and treatment, with photos of the actual stone.