Buying Birthstone or Colored Gemstone
Natural gemstones are found in nature. Laboratory-created stones, as the name implies, are made in a laboratory. These stones, which also are referred to as laboratory-grown, manufacturer-created, or synthetic, have essentially the same chemical, physical and visual properties as natural gemstones. Laboratory-created stones are not as rare as naturally mined stones and are therefore less expensive. By contrast, imitation stones look like natural stones in appearance only, and may be glass, plastic, or less costly stones. Laboratory-created and imitation stones should be clearly identified as such.
Gemstones may be measured by weight, size, or both. The basic unit for weighing gemstones is the carat, which is equal to one-fifth (1/5th) of a gram. Carats are divided into 100 units, called points. For example, a half-carat gemstone would weigh .50 carats or 50 points. When gemstones are measured by dimensions, the size is expressed in millimeters (for example, 7×5 millimeters).
Gemstone treatments or enhancements refer to the way some gems are treated to improve their appearance or durability, or even change their color. Many gemstones are treated in some way. The effects of some treatments may lessen or change over time and some treated stones may require special care. Some enhancements also affect the value of a stone, when measured against a comparable untreated stone.
Natural and cultured pearls are made by oysters and other mollusks when an irritant is introduced into the shells and causes a pearl to grow. Cultured pearls are created when the irritant is introduced by human intervention. Imitation pearls are man-made with glass, plastic, or organic materials. Because natural pearls are very rare, most pearls used in jewelry are either cultured or imitation pearls. Cultured pearls, because they are made by oysters or mollusks, usually are more expensive than imitation pearls. A cultured pearl’s value is largely based on its size, usually stated in millimeters, and the quality of its nacre coating, which gives it luster.