Gem Nation -- Glossary of Diamond, Jewelry and Watch Terminology 
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Carat is often confused with size even though it is actually a measure of weight. The cut of a diamond can make it appear much larger or smaller than its actual weight. One carat weighs 200 milligrams. As the relative weight of a diamond increases, so does its per carat cost. See discussion on carat.
Cavities are natural surface indentations or nicks occurring outside the diamond and expanding towards the inside.
Every Gem Nation diamond is accompanied with an original certification report from one of the world's leading certification authorities - the GIA (Gemological Institute of America), the AGS (American Gemological Society) or the EGL (European Gemological Laboratory).
A watch featuring a chronograph provides for the timing and aggregation of events. Most chronographs feature three separate dials that provide for timing aggregation in units of 1/10th of a second (up to 1 second), 1 second (up to a minute) and 1 minute (up to 30 minutes or an hour).
Not to be confused with the term "chronograph", this term refers to a watch that has undergone a series of precision tests by measuring the watch's timekeeping abilities in various horizontal and vertical positions. These tests are performed by the C.O.S.C., a Swiss testing agency, which issues a certificate upon successful completion. The C.O.S.C. certificate will accompany the watch in its packaging.
Clarity is a term used to describe the absence or presence of flaws (blemishes or inclusions) inside or on the surface of a diamond. Inclusions (inside the diamond) may take the form of crystals, cracks, clouds, growth lines, and cavities. Surface blemishes may include scratches, nicks, pits, abraded facet edges, extra facets and naturals. See additional information on Clarity.
  Clarity Enhancement
Clarity enhancement refers to the practice of filling the fissures that may be present in a diamond with a solid substance, such as a glass, that reacts to light in ways similar to diamond. As a result, the fissures become much less visible, which improves the apparent clarity of the diamond. Gem Nation does not sell clarity enhanced diamonds.
Clouds are made up of microscopically small dust-like crystals. When they are small and spread out, they diminish the clarity of the diamond only slighly. When they are large and close together, they influence the transparency and brilliance of the diamond.
The GIA (Gemological Institute of America) has established an industry-accepted color grading system that rates diamonds with alphabetical letters ranging from D (no color), the most expensive through Z (yellow). If you plan to mount the diamond in a platinum or white gold setting, you may wish to choose a color from D through H. Colors below H have a slighly yellowish hue which appear more yellowish in platinum or white gold settings and are therefore best suited to yellow gold settings. See additional information on Color.
Corundum is the crystalline form of aluminium oxide and one of the rock-forming minerals. Corundum is naturally clear, but can have different colors when impurities are added. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire. The word corundum comes from the Hindi kurand.

Corundum (9.0 on the Mohs hardness scale) is second only to diamond (10.0) in hardness.
The portion of a cut stone above the girdle.
Crystal inclusions are minerals that are included in the diamond. Depending on their nature, they may be colorless, redish, brownish, yellowish, greenish or black and may vary in size from a pinpoint to easily discernible crystalline inclusions.
The facet on the bottom of a diamond. It is best to have no culet, followed by a very small, small, or medium culet. A large or very large culet will most likely be visible to the naked eye and may make the stone appear to have a hole in the bottom and .
Cut refers to a diamondís reflective qualities not its shape. A well-cut diamond will reflect most light back to the observerís eye. A poorly cut diamond will reflect only a small proportion of light that enters it. See also discussion on cut.

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