How inclusions affect cost

Diamonds are graded on four criteria: cut, color, clarity and carat weight. Each of these factors helps determine the worth of the gem. Diamond grading processes asses each feature. When you purchase diamonds, you should also know something about the four Cs. Here's a specific look at clarity:

Inclusions

As gemstones form beneath the surface of the earth, they may develop imperfections known as inclusions. They are created when foreign minerals are lodged in the crystal as it is shaped. For example, diamond is made from carbon. If a mineral other than carbon is present in the crystal the final product will look as though it has a birthmark. Though they are generally the result of additional minerals, inclusions can also occur because of the presence of water, gas or petroleum. Additionally, these imperfections can happen organically from a skewed gem structure, internal factors or inconsistent color.

Types of formation

According to the Canadian Institute of Gemology, there are three basic types of inclusions that can be found in various gems.

Antegenic: In this case, the inclusion is formed before the host crystal has been made. The host then forms around the inclusion.

Syngenetic: With syngenetic inclusions, both the inclusion and the gem form at the same time.

Epigenetic: These are formed after the host.

Gem value

The number or type of inclusions affect a gemstone's value. Diamonds typically lose worth if they have an inclusion. In fact, diamonds without blemishes are incredibly rare, though most imperfections can often only be seen with magnification. Buyers can use this to their advantage by purchasing a blemished diamond more cheaply than a perfect one.

Flawless diamonds are given the highest value, and Included (I1, 2 and 3) are given the least. Other designations - from high to low value - include Internally Flawless (IF), Very, Very Slightly Included (VVS1 and VVS2), Very Slightly Included (VS1 and VS2), and Slightly Included (SI1 and SI2).

Other gems

Most gems lose value if they have inclusions. However, some gems are prized for their interesting features. For example, sapphire and ruby often have an inclusion called "silk." The crystal forms thin, needle-like structures that reflect light in an interesting way. In fact, these gems produce something called the "star effect" where viewers can discern a six-ray star pattern in the sapphire. This can only occur if the gem has silk inclusions. For this reason, the inclusion is often prized. However, it's a rare exception to the rule that inclusions devalue stones.