Gemstone Value and Inclusions


It's a common misconception among gemstone buyers that inclusions are to be avoided. This view is fostered by simplified gem buying guides that offer the advice that the fewer the inclusions, the better. Though this advice is certainly true for diamonds, it is not sound advice in the world of colored gemstones. Rejecting a colored gem because of some minor inclusions could mean missing out on a top grade stone. Clarity grading for colored gems are quite different from grading for diamonds.

Star Ruby Vietnam 13.32 cts
Star Ruby

There are very few colored gemstones which are internally completely "clean." Gemologists use the term inclusion to refer to foreign matter or irregularities of the crystal lattice in a gemstone. Note that gemology uses the term inclusion rather than "defect" or "flaw" to refer to these phenomena. For often they are not flaws at all. Sometimes they actually contribute to the beauty or value of the gem. They also provide important clues to the origin or formation of the stone.

One of the most famous and valuable gemstone inclusions is the organic matter trapped in amber. Amber is the fossilized, hardened resin of the pine tree, formed about 50 million years ago. Specimens with included insects or plant materials are especially valuable.

Rutilated quartz is another gem variety that draws its value from its characteristic inclusions. Rutile is the mineral name for natural crystals of titanium dioxide. While most varieties of transparent quartz are valued most when they show no inclusions, rutilated quartz is valued specifically for the lovely patterns formed by the delicate golden needles of rutile.

Demantoid Garnet Horsetail Inclusion
 Demantoid Garnet
Horsetail Inclusion

Inclusions of rutile add value to another group of gemstones: those that exhibit asterism (the star effect) or chatoyancy (the cat's eye effect). When aligned needles intersect at the right angle, a star sapphire or ruby will display six white rays of light that meet at one point and dance over the gem's surface when viewed from different directions.

Even in the transparent gems there are inclusions which are especially valuable. Fine rutile silk in corundum from locations such as Kashmir and Burma lend especially fine sapphire and ruby a velvety color that is highly prized. A unique horsetail inclusion in rare Russian demantoid garnet is regarded by collectors as the most reliable indication of Russian origin, since the more common Namibian demantoid lacks this unusual inclusion.The Russian demantoid typically has inclusions of byssolite or chrysotile in the form of feathery golden threads that tend to curve and resemble the tail of a horse. These inclusions are highly prized by collectors.


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