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Gemstone collection

Gemstones come in a virtual rainbow of colours, from pale yellow to crimson red. Some present a subtle hint of colour, while others are entirely saturated with a deep rich hue. 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.

Coloured Gemstones are often enhanced in the production process. Coloured Gemstones offered by Costco have been enhanced unless otherwise stated. Commonly used treatments used to improve or alter the colour of a gemstone can include heating or dying. In order to meet Costco's strict quality standards, all of our gemstone jewellery 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”).

Gemstone Grading

The value of a gemstone is determined by the overall evaluation of four key characteristics: colour, 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.


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


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.


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 colour, clarity and brilliance. A well-cut gemstone should be even in colour, have proportioned facets, and a smooth lustrous surface. There are five possible ratings for cut: poor, fair, good, very good, and excellent.


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.

Treatments & Production

Most coloured gemstones on the market today, have had some degree of treatment during the production process. The most common treatment or enhancement is heating, which is done to intensify colour and improve overall appearance. Unless otherwise stated, all coloured Gemstones offered by Costco have been treated during the production process. Lab-created emeralds are the only synthetic gemstone carried by Costco. Natural emeralds are incredibly rare and therefore, extremely expensive. That’s why the majority of emeralds found in the marketplace are lab-created emeralds. Due to the skill and expense involved in production, emeralds are among the most expensive lab-created gemstones available. Unless otherwise stated, all emeralds offered by Costco are lab-created.

Care & Maintenance

Avoid extended exposure to direct sunlight, extreme heat, or sudden temperature changes as this may cause the gemstones to fade or break. Gemstones vary in hardness and are susceptible to becoming scratched. It's important to wear and store your gemstone jewellery with care. Avoid all harsh chemicals such as bleach, ammonia and hair spray as they may damage metal and gemstones.

Most gemstone jewellery can be gently cleaned with warm water, a small amount of mild soap, and a soft-bristle brush or cotton cloth. Rinse the jewellery thoroughly, and ensure that it is completely dry before storing or wearing. Commercial jewellery cleaners are generally safe to use on most gemstone jewellery; however, some solutions do contain chemicals that can cause permanent damage to sensitive gemstones. Use with caution.