Types of Gemstones

There are three primary types of gemstone products:

• Natural gemstones occur in nature and can be rare and expensive.
• Laboratory-created stones — which also are referred to as synthetic, laboratory-grown, or manufacturer-created — have the same chemical, physical, and visual properties as natural gemstones, but they aren’t as rare and often are less expensive than natural gemstones with similar characteristics.
• Imitation stones look like natural stones, but may be made of glass, plastic, or other less costly material.

Laboratory-created and imitation stones should be clearly identified as such.

Size

Gemstones may be measured by weight, size, or both. The basic unit for weighing gemstones is the carat, which is equal to one-fifth 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 often is expressed in millimeters (for example, 7x5 millimeters).

Treatments and Enhancements

Gemstone treatments or enhancements refer to the way some stones are treated to improve their appearance or durability, or even change their color. The effects of some treatments may lessen or change over time, and some treated stones may require special care. Some enhancements affect the value of a stone when measured against a comparable untreated stone.

Here are some common treatments and their effects:

• Heating can lighten, darken, or change the color of some gemstones, or improve a stone’s clarity.
• Irradiation can add color to colored diamonds, certain other gemstones, and pearls.
• Impregnating some gemstones with colorless oils, wax, or resins hides a variety of imperfections to improve the stones’ clarity and appearance.
• Fracture filling hides cracks in gemstones through an injection of colorless plastic or glass to improve the stones’ appearance and durability.
• Diffusion treatment adds color to the surface of colorless gemstones; the center of the stone remains colorless.
• Dyeing adds color and improves color uniformity in some gemstones and pearls.
• Bleaching lightens and whitens some gemstones, including jade and pearls.