An Introduction To Gemstone Inclusions

Gemstone Inclusions - Apatite in Spinel
This rounded apatite crystal displays interference colors between crossed polars in a Burmese spinel. “Natural Spinel, Tanzania; Mahenge.” Photo by E. Billie Hughes. © Lotus Gemology. Used with permission.

Magnification opens the door to a fascinating dimension in gemology: the inner world of gemstone inclusions.  You’ll see marvels that can rival the beauty and intrigue of the gem itself. On a practical level, identifying inclusions may help you identify the gem species. They can reveal how a gem was formed and whether it’s a natural or synthetic stone. Some gems have specific inclusions that their lookalikes lack. Some inclusions only occur in a single gemstone species or even in a single mine!

What Are Gemstone Inclusions?

Simply put, an inclusion is any material that is trapped inside of another mineral while that mineral forms. Gemstone inclusions may be comprised of crystals of other minerals, liquid or gas bubbles, or even fractures caused by radioactive material contained within the host material. A listing of inclusions can never be complete. New inclusions and varieties are discovered constantly.

Gemstone Inclusions - Petroleum in Quartz
“Quartz with Petroleum Inclusions” by Luciana Barbosa is licensed under CC By-SA 3.0

Viewing Gemstone Inclusions

Inclusions are instrumental in identifying many species of gemstone. Nevertheless, viewing inclusions can be difficult. A microscope, preferably one with dark-field illumination, is often used to study them. While many inclusions can be resolved with a magnification of 30-60X (the range of most stereoscopic microscopes), some of the tinier ones require magnification of 200X or more.

Knowing how to use your microscope and various lighting techniques are essential skills for identifying inclusions. However, getting tiny details into sharp focus is often challenging and sometimes impossible. It’s easy for student gemologists to jump to conclusions about what they may see through magnification.

Gemstone Inclusions - Diamond Inclusions
Diamond Inclusions

Learning How To Distinguish Gemstone Inclusions

Discretion is essential. For example, can you make out the inclusion in the garnet pictured below? It’s difficult to tell if the ends are terminated or if they’re bubbles. As it turns out, they’re terminated, meaning the inclusion is a crystal. Crystal inclusions indicate a natural garnet. Bubbles would indicate a cheap synthetic. Identifying this inclusion correctly would be critical.

Gemstone Inclusions - Crystal in Garnet
Crystals or bubbles?

If you can’t see an inclusion clearly enough to distinguish its features, don’t base an identification on it. If you’re in doubt, look at all the available clues. A standard gemstone identification procedure should yield enough information to make a proper identification.

Learning to locate inclusions and distinguish their varieties takes practice. Pictures and descriptions are just guides. Gemology students should examine as many gemstones as possible. Use your loupe first and then your microscope. Keep practicing until you’re an expert at finding and identifying inclusions.

More Resources For Identifying Gemstone Inclusions

The International Gem Society (IGS) four-part series of Members Only Premium articles on gemstone inclusions documents the primary varieties commonly used for gemstone identification.

Gemstone Inclusions - Dolomite and Rutile in Quartz
For more stunning photographs of gemstone inclusions like this one, see our article on gemstone photomicrography. “Dolomite in Quartz with rutile, Minas Gerais, Brazil.” Photo by Danny Sanchez. Field of view = 5.2mm • Depth of field = 2.25mm.