The most valuable diamond is the white variety.
There are two gemstone categories used in the commercial gemstone trade: precious gemstones, which are diamonds, rubies, emeralds and sapphires, and semi-precious gemstones, which are all the rest. The latter include such gems as amethyst, beryl, garnet, lapis lazuli, topaz, tourmaline, turquoise, zircon and many others. Although each variety of gemstone has a color for which it is best known, almost all gems can occur in a number of different colors.
Diamonds and Their Colors
Diamonds are found in only one type of rock, kimberlite, which has formed over billions of years from a volcanic pipe. They may also be found in the gravel of stream beds, where they have been washed downstream from an eroded kimberlite pipe. Diamond is the hardest naturally occurring substance, and is a form of pure crystallized carbon. The purest and most valuable diamonds are colorless or white diamonds. Trace elements within the diamond lattice crystal structure can give the gem a number of different colors. For example boron can give a blue color, nitrogen a yellow color. Colors can also be caused by irradiation (green diamonds) or by plastic deformation of the lattice structure, which can give brown, pink and red hues.
Emeralds, Rubies and Sapphires
Emeralds are a strain of the mineral beryl, or beryllium aluminum silicate. Their green color is derived from the trace elements chromium or vanadium. The color can range from a yellow-green to a blue-green. Only gems that are medium to dark in tone are considered emeralds. All others are classified as semi-precious golden beryl when a golden yellow color, morganite when pink or aquamarine when blue or bluish-green.
Rubies and sapphires are varieties of the mineral corundum, or aluminum oxide. When corundum is deep red in color it is called ruby, and when it is any other color it is called sapphire. Sapphires can range in color from pale pink to violet, the color being dependent on trace elements of chromium, titanium or iron.
Semi-Precious Gemstones
In the same way as precious stones, all semi-precious gemstones have a most common color with which they are generally associated. Amethysts are usually a natural violet color, but can lose their color almost completely in bright sunlight. Garnets are usually a deep red color, but can be orange or even green, but never blue. Topaz, a fluorine aluminum silicate, is usually yellow-brown, but can be green, blue, pale blue, pink and even red. In all cases the color of the different "species" of each gemstone depends on trace elements that have combined with the crystals. The colors of many gemstones can be enhanced or even changed when they are either heated or irradiated.
Value
The value of a diamond depends upon the four Cs -- cut, color, clarity and carats. The closer a diamond is to being completely colorless, the more rare and expensive it will be. Clarity goes hand in hand with color. A badly cut diamond will not be as valuable as one that is well cut, and that the more carats, the more expensive.
Like diamonds, other gemstones are valued according to the four Cs. Precious stones -- emeralds, rubies and sapphires -- are in a different class from semi-precious gemstones, but still rely on the four Cs. A gemstone's color can be altered by irradiation, and some unscrupulous dealers have been known to alter a stone's color in order for it to appear to be more attractive and hence more valuable.
Tags: aluminum silicate, color called, deep color, different colors, elements chromium, gemstone color