Identifying Inclusions of Specific Gems
Some natural as well as synthetic gems have specific, characteristic inclusions. Learn the identifying inclusions of some of the most popular gems.
13 Minute Read
Beryl and Tourmaline
Both beryl and tourmaline develop hollow or "growth" tubes. Gem cutters see many more of these than gemologists do, since they cut away most of these inclusions. While these tubes begin hollow, they may be filled with opaque, white minerals later, as the crystal develops.
You can easily distinguish growth tubes from other inclusions. They have even sides and run straight for considerable distances. When present, you can assume these inclusions indicate a gem is most likely a beryl, tourmaline, or possibly spodumene. A refractive index (RI) reading can then distinguish these minerals.
Silk in Hexagonal Patterns
Silk is the most distinctive of corundum's inclusions. What gemologists call "silk" consists of very fine threads (crystals) of another mineral, rutile. If you can see enough of these inclusions, you'll note they form a hexagonal pattern. If you can only see part of the threads, they meet at 60° or 120° angles.
Donald Clark, CSM IMG
The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”
Specific Gravity Testing Part 4: Refining Your Specific Gravity Testing Techniques
Buying Gems: Test Your Identification Skills
Emerald Fillers and Treatments
Destructive Gemstone Tests: Acid Testing
How Does Quartz Form?
Azurite Value, Price, and Jewelry Information
An Introduction to the Lapidary Arts
Crystalline Quartz Buying Guide
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
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!