Clarity
Clarity is one of the four "C's" that determine the value of a diamond and refers to a stone's purity. Clarity is evaluated by viewing the stone under ten-power (10x) magnification. Virtually all diamonds contain tiny, natural birthmarks that are present in varying degrees when they are formed. These marks serve as the identifying "fingerprint" that makes every diamond unique.
"Naturals" are those marks found on the exterior of the stone, while "inclusions" refer to anything that is trapped within the diamond crystal. Nearly all diamonds, even those of the highest quality, have some impurities which fall into these categories:
Mineral Inclusions A dark spot from a trapped bit of mineral.
Naturals Open cavities, part of the original diamond crystal, that interrupt the diamond's exterior surface.
Feathers Internal cracks or fractures caused by either internal or external stress during the diamond's formation.
How Clarity is Graded
While there are several grading systems used in the industry, the most recognized and commonly-used system is the one developed by the Gemological Institute of America (GIA).
FL-Flawless shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader. Extremely rare.
IF-Internally Flawless has no inclusions when examined by an experienced grader using 10X magnification. Very rare.
VVS1, VVS2-Very, Very Slightly Included contains minute inclusions that are difficult, even for experienced graders, to see under 10X magnification.
VS1, VS2-Very Slightly Included contains minute inclusions when observed with effort under 10X magnification.
SI1, SI2-Slightly Included contains inclusions that are noticeable to an experienced grader under 10X magnification.
I1-Imperfect has obvious inclusions that are visible without magnification, but not at a quick glance.
I2,I3-Imperfect has obvious inclusions that are visible without magnification.
As a rule, the less visible the location of the inclusion, the less impact on the stone's value.
Carat Weight
Diamonds are sold by the carat (ct), a unit of weight, not size. The size of a diamond is defined by its weight, expressed in carats. One carat weighs one-fifth of a gram and is divided into 100 points. The larger the diamond, the more rare and costly it is. However, depending on their color, clarity and cut, two diamonds of the same carat weight can vary widely in their value.
The word carat is derived from the Arab word for carob; carob seeds were used in early trading days to determine the weight of diamonds. While this method may seem unscientific, the carob seeds were so uniform in size and weight that they produced highly reliable measurements. Today, we use very sensitive, accurate scales to measure the weight of a diamond.
One carat weighs 200 milligrams, or one-fifth (.2) of a gram. This standard has been in use worldwide since 1914, when it was proposed by the International Committee on Weights and Measures. Note that the term "carat", which is a measurement for precious gems, differs from the term "karat," which refers to gold quality in the United States.
When discussing stones of less than one carat, jewelers often refer to the weight in terms of points. A carat is divided into 100 points, with one point corresponding to .01 carat. Think in terms of pennies to a dollar. There are one hundred pennies in a dollar, and there are one hundred points in a carat. Therfore, a 1/2 carat stone equates to 50 points, a 1/4 carat diamond is 25 points. Very small stones, such as those used in pavé or channel settings, are sometimes called melee. Melees range from .01 to .16 carat in weight.
Although the analogy of pennies to the dollar suggests that one carat is always 100 points, or that one-half carat is always 50 points, that's not always the case. Diamonds can't all be uniformly cut to such exact weights, so there are approximate weight ranges for diamonds of a given size.
Since diamonds become rarer as they increase in weight, the larger the diamond, the more valuable and expensive it usually is. However, the price of a diamond does not increase at the same rate as its weight. The larger the stone, the more disproportionate the increase in cost per carat. For example, a 2-carat diamond is always more expensive than two 1-carat diamonds of the same quality.
When evaluating diamonds, weight and size are not the same thing. Yet, carat weight has come to represent particular sizes when based on a well-cut diamond. Since ancient times, diamond cutters have sought to produce a diamond of maximum possible weight and quality from the rough crystal.
Also, see our article, "How to Buy a Diamond-Cut and Color"
http://www.bellaonline.com/articles/art48379.asp
Reference: Barbara W. Smigel, PhD.,GG - Certified Gemologist http://www.bwsmigel.info
