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As with diamonds, the unit of weight and size for natural gemstones is the carat and the relationship of size and weight is different for each family of precious gemstones. Many natural gemstones are heavier and have a higher specific gravity than diamonds, for example. A one carat precious gemstone may be smaller in size than a one carat diamond. As carat weight increases, so does the price of the gem.
Natural Gemstones, like diamonds, come in a variety of shapes. Precious Gemstones are generally cut differently and deeper than diamonds, however, with more weight in the bottom to bring out the intensity of their color. Different types of shapes are suitable to different families of gemstones. Sapphires unlike diamonds, for example, are generally shaped into ovals or cushions to preserve their raw proportions and retain maximum weight.
Precious gemstones measurements are generally listed in millimeter units or carat weight and their specific gravity/density differs from that of diamonds—a stone’s size varies depending on its specific gravity. As a result, a one carat gemstone will not look the same size as a one carat diamond. Unlike diamonds, natural gemstones tend to be unique.
Enhancement is a process used to improve the appearance and durability of most natural gemstones on the market. Quality enhancements are permanent and include heating to enhance color and coating to improve durability.
Pink is the rarest of the sapphire colors and generally the most valuable. Pink sapphires, which have qualities similar to rubies, are very durable and range in color from pale pink to magenta, and may have violet undertones. Color is a crucial factor when pricing pink sapphires—the more vivid and clear the color, the more valuable the stone, and deeper tones tends to have more inclusions.
Yellow sapphires resemble yellow diamonds and are available in many color nuances, from light lemon yellow to canary yellow, to greenish-to-orange yellow. Yellow sapphires tend to have fewer inclusions than blue and pink varieties and their price depends on their size, quality and color—with pure golden yellow being the most valuable.
Blue is the most popular and traditional color choice for sapphires. Blue sapphires come in variety of hues and tones and are evaluated and priced according to the purity of their primary hue, and their carat weight. One advantage of blue sapphires is their durability—they have a hardness of 9 on the Mohs scale of mineral hardness.
Rubies range from pink to blood-red in color and are among the most valued of natural gemstones on the market, with color being the primary determinant of price, and clarity the second factor. Rubies are hard and durable (9.0 on the Mohs scale of mineral hardness). Most rubies contain visible inclusions and symmetrical, round ruby cuts are considered the most flattering and valuable.
Emeralds range from medium or dark green to bluish-green in color. Emeralds as a general rule possess inclusions, although clarity is less a factor in their valuation than color is. Emeralds are physically larger than diamonds and rubies of similar weight and are typically cut to preserve most of their original size, and may therefore be available in unusual shapes.