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Precious Gemstones
Some gemstones are considered to be more valuable than others and as such, they are categorized as precious gemstones. The issue of whether a gemstone is precious or semi-precious is determined by certain factors such as rarity of the gemstone, extraordinary color and the established market value. The four gemstones that are considered to be precious are diamond, ruby, sapphire and emerald. Amethyst was once considered to be a precious stone, until large deposits were discovered in Brazil and Uruguay in the first half of the 19th century. It was then relegated to the position of a semi-precious stone. However, it is interesting to note that equally large deposits of diamonds were discovered in South Africa in 1870. Still, diamonds continue to be classified as "precious" due to the creation of the powerful De Beers cartel, which controls how many diamonds are released into the market, thereby keeping the price of diamonds high by propagating the myth of rarity.
Semi-Precious Gemstones
Semi-precious is a term reserved for all other colored gemstones, excluding the four precious gemstones. Most of these semi-precious gemstones have quality gemstone characteristics comparable to precious gemstones. Some of the desirable qualities include brilliance, intensity of color, clarity and hardness. Some of these semi-precious stones include tanzanite, amethyst, spinel, tourmaline, rose quartz, peridot and rhodolite.
Organic Gemstones
Some gemstones are made of organic materials rather than minerals. This means they were formed from vegetable or animal matter. Examples of this category of gemstones include pearl, amber, jet, coral and ivory. Amber is the result of fossilized resin formed from ancient pine trees dating back to more than 50 million years. An interesting fact is that the more precious amber samples are those that have pieces of prehistoric plants, insects or pyrites trapped inside.
Synthetic Gemstones
Synthetic gemstones are imitations of gemstones that are created through artificial processes. The main difference between synthetics and real gemstones is the fact that natural gemstones are formed naturally while synthetics are not. However, good synthetics can resemble the original gemstones in every way that counts, such as chemical composition, crystalline structure, color saturation and specific gravity. Some gemstones that have synthetic versions include diamond, amethyst, sapphire, ruby, opal and pearls. A familiar example of an imitation gemstone is cubic zirconia, which is an imitation diamond.