Curved striae are sure signs of synthetic ruby and sapphire. However, seeing them can be difficult because the curvature of the lines can be very subtle. The striae shown here are from a synthetic sapphire. “Curved Striae” by stonespecialists.

Curved striae are sure signs that rubies or sapphires, like the one photographed here, are synthetics. However, seeing these inclusions can be difficult because the curvature of the lines can be very subtle. “Curved Striae” by stonespecialists.


Are there any tricks to finding the curved striae or lines in synthetic ruby and sapphire? Sometimes I have trouble finding them.

Thanks in advance,



On several occasions, I’ve noticed I could find the zoning lines of natural corundum, rubies and sapphires, more easily with a polariscope. Sometimes, these lines aren’t easily visible under a standard 10X loupe. If you have a polariscope, try it. It may work for the curved striae in synthetic ruby and sapphire. If you don’t have a polariscope, you can make a cheap one. And don’t be afraid of using your loupe between the polarizing lenses.

A polariscope helps you locate the C axis of a crystal rather easily. If you use a polariscope to locate the C axis of a synthetic ruby, for example, then at least you’d expect the lines to be curved if you see them while looking down that axis. If you don’t look down the C axis, you may see straight lines that are actually curved. (Especially if you look at them at an angle perpendicular to the C axis).

Additionally, Richard Liddicoat recommended immersing a stone in methylene iodide or bromoform in a jar. This makes it easier to view the striae while using a white sheet of paper under the jar as a background.


Ryan Young (Hobbyist Gemologist/Mineralogist and Enthusiast)