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Diamonds,
the best known and most popular gemstones, are composed of a single element - carbon. They have a degree of hardness unequaled in the mineral kingdom. Fortunately this extreme hardness varies in different directions of the crystalline structure - it would be otherwise impossible to cut them.
The value of cut diamonds is determined by an international, extremely rigid system of evaluation known for simplicity's sake as "the Four C's": colour, carat, cut and clarity. Most highly valued are the colourless diamonds, especially those with a barely discernible bluish tinge. A subtle colour scale ranges from blue-white through white and yellow to brown diamonds.In addition to these "normal colours", there are "fancy diamonds" of various colours, such as green, red, blue, pink, brown, cognac and yellow. Because of their rarity they are held in very high esteem, especially when the colour displays an intense saturation.
The weight of diamonds is measured in carats, a standard unit of weight which corresponds to .20 gram.
A wide range of cuts are applied to diamonds. The most common, which brings out the natural "fire" most fully, is the so-called brilliant cut. Favourite fancy cuts are the eliptical marquise cut, the rodlike baguette cut, the emerald cut, and the drop form.
By international agreement, inclusions in diamonds are regarded as diminishing their value only when they are pronounced enough to be visible through a lens or loupe with a tenfold magnification. Otherwise diamonds are described as "loupe clear" or internally flawless.
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