Identifying Inclusions of Specific Gems

Step 2: Advanced Gemology

Lesson 12

identifying inclusions - blue gemstone

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.


Rubies and sapphires, both corundum gemstones, are some of the easiest gems to identify by their inclusions.

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.

Garnet gems contain similar but coarser inclusions. They meet at 70° or 110°. On the other hand, …

Premium Article

This is a Premium Article. Please become a member to read this entire article and gain access to hundreds more like it.

Membership options

Full Article Details

Content Length 2881 words
Reading time 14 min 24 sec

Here's what you get if you unlock this article:

  • Beryl and Tourmaline
  • Corundum
    • Silk in Hexagonal Patterns
    • Other Hexagonal Patterns
    • Fingerprints and Crystal Inclusions
    • Stress Fractures
    • Inclusions of Thai and Burmese Corundum
  • Cubic Zirconia
  • Diamond
    • Bearded Girdle
    • Natural Girdle
    • Trigons
    • Graining
  • Enhanced Diamonds
  • Synthetic Diamonds
  • Natural Emerald
  • Synthetic Emerald
  • Garnet
    • Spessartite Garnet
    • Hessonite Garnet
    • Demantoid Garnet
  • Natural Glass
    • Obsidian
  • Glass Imitations
  • Cat's Eye Gems
  • Imitation Jade
  • Ivory
  • Lapis
  • Moonstone
  • Opal
    • Chicken Wire Pattern
    • Confetti
    • Pepper Spots
    • Soot
    • Plastic Opal Imitations
    • Gilson Opals
  • Pearls
  • Peridot
  • Plastic
  • Quartz
  • Spinel
  • Turquoise
  • Zircon
  • More Resources for Identifying Inclusions

Plus, additional member-only benefits:

  • Exclusive access to other premium articles and courses
  • Unlimited access to our gem pricing guide
  • Participate in our member-only forums
Membership options