An Introduction to Gemstone Inclusions
It's the moment she's been waiting for her whole life. He's there, down on one knee, with a velvet-lined box and a question. Yes, of course yes! He slips the sparkling diamond ring on her finger, and she look down to admire its beauty. As she stares at the large solitaire, she can only think of one thing - what is that black dot right in the middle of my precious diamond?!
Gemstones are formed in incredible circumstances, be it by heat, pressure, erosion, or all of the above. These processes leave their fingerprint on the stones in the form of inclusions. Inclusions are clarity characteristics that are entirely enclosed within the gem or that break into the gem from the surface. They may be the same material as the gem itself, or a completely different mineral. To some, the term inclusions have a negative connotation, like the black spot in the diamond mentioned earlier. But there is more than meets the eye to these "flaws."
Inclusions can be solid, liquid, or gas. You might find rough garnets inside of a diamond, or negative crystals (enclosed cavities) hiding inside of a sapphire. In some cases, all three types of inclusions can be found in a single gem, like the three-phase inclusions in prized Colombian emeralds. Looking through a microscope, many gems that appear fairly clean to the unaided eye suddenly turn into alien landscapes and abstract works of art. Miniature centipedes may march inside of your glowing moonstone. Rutile needles can look like strands of golden hair or thread within a clear quartz crystal. A vibrant fire opal can become a glowing orange sunset when inclusions align just right. But these inclusions are more than just a visual treat.
Suppose you see a display of three green gemstones. They share the same style of cut, are the same weight, and appear roughly the same color. To the untrained eye, they may appear to be identical stones. However, by looking inside each gem, you can gain clues to their identity. That first gem is filled with dainty discs that resemble lily pads in a pond - you can confidently say that it is a peridot. The next seems to contain miniature hairs that flare out like the tail of a horse - it is a rare demantoid garnet. The third is filled with tiny bubbles that form perfect spheres - alas, the last stone is merely glass or a synthetic imitation.
Not only can they help identify the gem, but inclusions can also provide clues to whether a stone is natural, synthetic, or even treated. The crystals trapped inside a sapphire, for example, may be a different mineral and thus have a different melting point that the host stone. When heat treatment is applied to improve the sapphire's color, it can melt these crystals and produce stress fractures. Conversely, the presence of undamaged crystals and needles suggest that the sapphire has not be introduced to intense heat. And while natural and synthetic gemstones are chemically the same, their inclusions can prove their origin. The remnants of the synthesis process can leave traces on the gem, like flux residue or gas bubbles found inside of synthetic emeralds. Furthermore, by identifying the synthetic inclusion, you can also learn what type of process created the gem. A bubble-filled flame-fusion ruby would typically be worth less than a flux-filled gem created by a more intensive and expensive process.
Inclusions can also interact with light and create spectacular effects known as phenomena. When microscopic needle-like crystals align within gems like ruby, sapphire, and spinel, it can produce a star pattern known as asterism. Similarly, the alignment of needles and tubes can create a cat's eye or chatoyant effect in tiger's eye, tourmaline, and diopside, among many others. Aventurine quartzcontains small green spheres of fuchsite mica that sparkle and shimmer, and sunstone may display entire rainbows due to inclusions.
The importance of inclusions extends far beyond the appearance of the gem. They can provide insight into the past and even the formation of the earth. Amber, an organic gem material created millions of years ago by the fossilization of resin (tree sap), can carry a wealth of information about the prehistoric world. Those who are familiar with Jurassic Park may remember that the dinosaur DNA was found inside of a mosquito trapped in amber, and the reality is not far off. Scientists can learn a great deal about the vegetation, wildlife, and even air quality from these unique inclusions. In some cases, entire extinct creatures have been found frozen in time. The recent discovery of an intact dinosaur tail has even confirmed the recent theory that some of these ancient beasts were covered with feathers. Diamonds, which are formed hundreds of miles below the earth's surface, have revealed valuable clues about the very depths of this planet. Through extensive study of the inclusions in "superdeep" diamonds, scientists have proven the existence of metallic iron deep inside the earth's mantle. These and many other discoveries made through gems help to clarify the geological evolution of the planet.
When purchasing a gemstone, be it rough or faceted, it is nonetheless important to understand how its inclusions may impact both the appearance and structural integrity of the stone. Fractures, often referred to as feathers, are weak points on the gem that make it susceptible to further damage and breaking. Similarly, cavities and chips are something to be wary of. Emeralds are one of several gems prone to extensive fractures, and can be quite brittle as a result. To improve their appearance and stability, these fractures are typically oiled and filled to make them less visible to the unaided eye. However, even these measures have their drawbacks. Emeralds should not be placed in an ultrasonic cleaner, which can destroy the fracture filling, and the filling itself can dry out and crack.
The type of inclusion and its positioning in the stone can have a great impact on the beauty of a specimen. A large inclusion directly under the table of a finished gem, for example, is far more noticeable than a similar inclusion hidden near the girdle. A feather may appear nearly invisible when it is perpendicular to the crown, yet that same feather could instead become a bright flaw if it broke at an angle. Inclusions can also reflect within a gemstone and make it appear more heavily included than it actually is. All of these factors can alter the value and appearance of your gemstone, so examine it carefully before purchase.
Despite their often negative reputation, inclusions are a fascinating and vital aspect of gemology. Eye-clean and "flawless" gemstones will continue to command some of the highest prices in the marketplace, but their included counterparts should not be overlooked. After all, who wouldn't want a unicorn, star, or cricket player inside of their diamond?
I love gemstones so much that I decided to make a career out of it. I received my Graduate Gemologist (G.G.) diploma in residence from the Gemological Institute of America (GIA). After finishing the program, I accepted a position as a diamond grader at the GIA laboratory and was selected to become a colored diamond color grader. Wanting to share my passion for gemology with the rest of the world, I transitioned to the education department and worked as a museum tour guide and GemKids program instructor. I have also worked on the retail end of the industry, both with modern and vintage jewelry.
