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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.
Gemstone Inclusions - Apatite in Spinel

This rounded apatite crystal displays interference colors between crossed polars in a natural Burmese spinel. Photo by E. Billie Hughes. © Lotus Gemology. Used with permission.

Gemstone inclusions can also 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. For example, crystals, liquid or gas bubbles, or even fractures caused by radioactive material in the host material may comprise gemstone inclusions. Since researchers constantly discover new inclusions and varieties, a listing of inclusions can never be complete.

Petroleum in Quartz

This quartz stone has petroleum inclusions. Photo by Luciana Barbosa. Licensed under CC By-SA 3.0

Viewing Gemstone Inclusions

Inclusions are instrumental in identifying many gemstone species. Nevertheless, viewing inclusions can be difficult. To study them, gemologists often use a microscope, preferably one with darkfield illumination. While a magnification of 30-60X (the range of most stereoscopic microscopes) may resolve many inclusions, 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 often proves quite challenging, if not impossible, in some cases. Sometimes, student gemologists can easily jump to conclusions about what they see through magnification.

Gemstone Inclusions - Diamond Inclusions

These drawings illustrate types of diamond inclusions.

Learning How to Distinguish Gemstone Inclusions

Gemstone Inclusions - Crystal in Garnet

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

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, because pictures and descriptions serve only as guides. Gemology students should examine as many gemstones as possible, with a loupe first and then a microscope. Keep practicing until you’re an expert at finding and identifying inclusions.

gemstone inclusions - peridot with ludwigite

Peridots can be identified by the presence of a “lily pad” type of inclusion. However, this peridot from Pakistan also contains needle-like crystals of ludwigite, a very rare mineral. © Rob Lavinsky, www.iRocks.com. Used with permission.

More Resources

Do you want to learn more about inclusions? The International Gem Society (IGS) has a four-part series of Members Only premium articles on gemstone inclusions that document 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 of dolomite in quartz with rutile, see our article on gemstone photomicrography. Photo by Danny J. Sanchez.