Star sapphire is one of the most extraordinary phenomena in the gemstone world — a star of light that glides across the surface of a cabochon-cut corundum when illuminated by a single point light source. The star is created by dense, precisely aligned rutile silk (microscopic titanium dioxide needles) inside the crystal, reflecting light in three directions that intersect at 60° angles to form the star.
Why our star sapphires
Our star sapphires are sourced from Sri Lanka, the origin of the famous Star of India (563 carats, now in the American Museum of Natural History) and the Star of Lanka (193 carats). Each stone here carries its own GIA report, and each stone's page states that stone's treatment finding in the report's own words rather than inferring anything from the star.
What a report says about a star sapphire, and what it does not
The star itself. A GIA colored-stone report records asterism as an observation: the phenomenon field reads Displaying Asterism. GIA states that it does not grade or provide quality analysis for sapphire or other colored stones, and no laboratory publishes a grading scheme for a star. So there is no laboratory grade for a star, and we do not publish an opinion of our own in place of one. Put the stone under one direct light source, tilt it, and judge it yourself — ask us for more photographs and video and we will send them.
Body color. Star sapphires occur in blue, gray, black, purple, violet, pink, yellow and white. The color on a stone's report is the laboratory's own color description of that stone; anything we add about color is our description and not the laboratory's.
Transparency. Star sapphires run from transparent to opaque. A GIA report prints the transparency it observed as a field value, and that field value is what each stone's page carries. We do not rank one transparency above another.
Cabochon shape. Star stones are cut as cabochons (a smooth, domed surface) rather than faceted, because the dome is the surface on which the reflections from the silk form a star instead of being broken up by facets. Dome height changes how the star reads, and it is one of the things to look at in the photographs.
Natural vs. synthetic. Synthetic star sapphires (often called Linde or Lindy stars) are common and inexpensive. Whether a stone is natural or synthetic is answered by a report field rather than by eye: a GIA report names the species and the variety of the material it examined, and each stone's page prints what its own report says. See How to Tell If a Star Sapphire Is Natural.
Heat, silk and the star
The star exists because of rutile silk. In faceted sapphires, heat treatment is used to dissolve that silk: above roughly 1,400°C it returns to the corundum lattice, releasing titanium to pair with iron and deepen blue color, and dissolving the silk takes the star with it. But heat does not run in one direction only. GIA publishes that heating can also recrystallize silk and make it more prominent, which lets a stone show a stronger star, and that titanium diffusion is used to create stars in sapphire. A visible star is therefore not evidence about a stone's treatment history in either direction. What a laboratory found is on that stone's own report, and each stone's page prints what its report says. For the full science, see How Sapphire Heat Treatment Works.
Learn about star sapphires
Star sapphire buying guides
The science behind the star
Engagement rings and custom jewelry
Reports and trust
Origin and sourcing
Comparisons
Have a question about a specific star sapphire? Email crescentgems@gmail.com. We can send additional photos and video showing the star under a direct light source. 14-day return on every order. Free US shipping; international shipping via FedEx and UPS.
