Clarity: Gemstone Purity
Nature does not create precious stones in an ideal environment; inclusions and imperfections are nothing more than marks of authenticity which document the gemstone’s relationship with the Earth.
Many gemstones are crystalline, and posses a ‘crystalline structure,' meaning they have a regular three-dimensional array of atoms. Most gemstones consist of a single crystal (macrocrystalline), such as Amethyst, Sapphire and Tourmaline.
Amethyst: single crystal (macrocrystalline)
Other precious gems have a crystalline structure so fine that it cannot be discerned, not even under a microscope, as being composed of distinct particles. Such gems, which include Agate, Chalcedony and Jade, are called ‘cryptocrystalline.'
Two opaque cryptocrystalline gemstones: Jade and Agate
Regardless of their crystalline structure, very few gemstones form undisturbed in nature. Their process of creation is often the result of major upheaval, which manifests as small natural ‘inclusions,' sometimes called ‘imperfections.' The latter term is inappropriate, as it implies defects rather than the minor imperfections, like those one might find in a silk coat, or in the knots in a piece of wood. These are, in effect, ‘natural characteristics,' marks of authenticity that document the natural relationship between a gemstone and the Earth.
Typical inclusions in Emerald, called ‘jardin.'
Inclusions are typically microscopic and more easily observed when enlarged, viewed either through a jeweler’s loupe or a microscope. The purity of a stone is determined by the quantity and distribution of its inclusions. For example, the clarity grades for a gemstone according to GIA (Gemological Institute of America) are: eye-clean, slightly included, moderately included, heavily included, and severely included. There are two general rules of thumb regarding clarity:
- The higher the clarity grade, the higher the value of the gem.
- Inclusions that don’t interfere with the brilliance, scintillation (sparkle) and fire of a gem, do not affect its value.
However, please be aware that attractive, characteristic or interesting inclusions can add value to a gemstone, for example asterism in Star Rubies.
Related to clarity, but influenced by a gemstone’s Chemical composition, crystal structure and inclusions, different gems inherently display different levels of opacity:
- Opaque is the quality of not allowing the transmission of light. Opaque gems include Agate, Jade and Onyx.
- Translucent gems allow transmitted light to pass through, but objects cannot be clearly seen through a translucent gemstone. Good examples are Fire Opal and Rose Quartz.
- Transparent gems allow transmitted light to clearly pass through. Objects can be seen through a transparent gemstone and examples include Amethyst, Sapphire and Tanzanite. As it directly affects the communication of color, the degree of transparency and brilliance is crucial in determining the value of transparent gems.
A precious ring with a Fire Opal
As you gain experience, you’ll begin to expect certain degrees of clarity from certain gems. Some gem varieties always have more inclusions than others. This is neither good nor bad; it’s just the way they are found in nature. To make sense of these natural differences, the GIA (Gemological Institute of America) classifies gems into three types based on the prevalence of inclusions:
- Type I These gems grow extremely clean in nature and usually have no eye-visible inclusions, for example Aquamarine.
- Type II These gems typically grow with some minor inclusions in nature that may be eye-visible, for example Ruby.
- Type III These gems typically grow with many inclusions in nature and they are usually eye-visible, for example Emerald.
Not all gemstones fit the GIA classification, only the major stones known at the time this grading system was developed. Translucent, opaque and cabochon stones do not fit. However, it would be incorrect to conclude that a Type III stone is intrinsically inferior to a Type I stone.