Jewelry Buying Guide Gemstones

Jewelry Buying Guide

Diamonds

Gemstones

Gemstones come in a virtual rainbow of colors, from pale yellow to crimson red. Some present a subtle hint of color, while others are entirely saturated with a deep rich hue. Throughout history, gemstones have been used to symbolize numerous things, from social status to important milestones. Many gemstones are identified as birthstones, others are considered a sign of wealth or nobility, while some gemstones are thought to bring happiness or protection. Today, most of us wear gemstones because we simply enjoy their beauty. So, whether you prefer to wrap your wrist in luxurious amethysts or adorn your hand with a sapphire engagement ring, you'll love the way a high-quality gemstone makes you look and feel.

In order to meet Costco's strict quality standards, all of our gemstone jewelry is thoroughly inspected by one of our Gemologists prior to shipping. All Costco Gemologists have graduated from a program with the Gemological Institute of America ("GIA").

Costco Gemstone Collection

Gemstone Grading

The value of a gemstone is determined by the overall evaluation of four key characteristics: color, clarity, cut, and size. There are other factors that may also affect a gemstone's value, including supply and demand, degree of treatments, and the rarity of the stone.

Color

Color is the most important characteristic of any gemstone. For many people, color comes down to personal taste. On a professional level, a gemstone's color is judged on its overall consistency, its richness and depth, and of course, its brilliance. For most gemstones, a color that is medium in tone, not too dark or too faint, is the most desired.

Cut

Each gemstone is unique, and should be cut in a way that best showcases its positive attributes. Many gemstones are cut simply for size, with little concern for other characteristics. But a talented gemcutter will choose a cut that strikes the perfect balance between color, clarity and brilliance. A well-cut gemstone should be even in color, have proportioned facets, and a smooth lustrous surface. There are five possible ratings for cut: poor, fair, good, very good, and excellent.

Clarity

Nearly all gemstones have internal flaws called inclusions, which are tiny pieces of material found within the stone. These inclusions can range from minor to severe, and can affect the look and strength of the stone. They are the key characteristic in determining the clarity of a gemstone. The fewer inclusions, the better the clarity.

Size

Because gemstones vary greatly in density, the standard practice of measuring weight in carats does not always give an accurate description of a gem's true size. More commonly, a gemstone's size is derived by measuring its length and width, or diameter, in millimeters. In some cases, a gemstone's size will be listed in both millimeters and general carat weight.