Seylan Gems & Jewelry
A star sapphire is sapphire, not a different mineral. Fine needles, usually rutile, reflect light as a star when the stone is cut as a cabochon with the silk in the right direction. Ceylon is famous for this material.
Specifications
Typical published ranges used in gemology. Specific gravity below matches our carat calculator default where applicable. (SG 4.00)
| Mineral | Corundum, the same as other sapphire |
|---|---|
| Hardness (Mohs) | 9 |
| Rays | Usually six; twelve-ray stars exist and should look like twelve |
| Cut | Cabochon, oriented to the silk |
| Specific gravity | About 4.00 |
| What you judge | Sharpness, centering, completeness of the rays, and body color |
Each ray should be visible, straight, and meeting at the center of the dome, not off to one side. The star should move smoothly when you tilt the stone under a single light. A star that only appears in a edited photo is not a star you can wear.
Body color still counts. A sharp star on a muddy gray stone is a different purchase from a sharp star on a blue or pink body. Silk that creates the star also limits transparency. That silky look is the cause of the effect, not an accident.
Star ruby is the red version of the same effect. Black star sapphire is a dark body with a star, not a metal. Glass and synthetic corundum can show stars too. Natural versus laboratory-grown belongs in the listing if there is any doubt.
Hardness is still 9, but a high dome can scratch other jewelry in a box, and a thin cabochon can chip at the edge if it is struck.
A true star is a cabochon effect. Faceted sapphires can show silk, but the rays people mean need the curved surface.
High heat can dissolve the rutile silk and the star with it. A star stone is usually unheated for that reason. Ask if a particular item states treatment.
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