Tips to Identify Striae in Synthetic CorundumTips to Identify Striae in Synthetic Corundum

Ruby Specialist Mini Course

Tips to Identify Striae in Synthetic Corundum

HomeCoursesRuby Specialist Mini CourseTips to Identify Striae in Synthetic Corundum
Question:Are there any tricks to finding the curved striae or curved lines in synthetic ruby and sapphire? Sometimes I have trouble finding them.

Purchase Ruby Specialist Mini Course

Do you love all things ruby? If you find yourself drooling over this king of gems, you’ll love this course. Take an in-depth look at rubies, from how they form to how to appraise them. Looking to buy or sell a ruby? Learn about ruby treatments and evaluating ruby quality. Every ruby lover will learn something new in this course.
Curved striae in synthetic ruby and sapphire
Curved striae. Photo by The Stone Specialists. Used with permission.

Answer: Curved striae are sure signs that a ruby or sapphire is synthetic. However, seeing these inclusions can be difficult because the curvature of the lines can be very subtle.

Using a Polariscope to Find Curved Striae in Synthetic Ruby or Sapphire

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 striae in lab-made 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).

Immersion Method

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)

Using Magnification to View Curved Striae

IGS Members can watch this video by Gem Geek for tips on viewing curved striae under a loupe or microscope.

International Gem Society

International Gem Society

Never Stop Learning

When you join the IGS community, you get trusted diamond & gemstone information when you need it.

Become a Member

Get Gemology Insights

Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!