The majority of gemstones are minerals - exceptions being pearls and coral which are of animal origin, and jet and amber which are vegetable. These minerals have been crystallized as a result of high temperature and pressure exerted by nature within the earth's crust. Of over 3000 minerals found on earth, only a small percentage qualify as gemstones due to their beauty, rarity, colour and durability.
Several factors should be considered when looking to purchase a gemstone:
Colour: The jewellery industry recognizes the highest quality gemstones by purity of their hue, the depth of tone, and the colour saturation. The best value is in colours that include 'slight' traces of other colours, are not too light or dark, and have a lot of saturated colour.
Clarity: Almost all gemstones contain tiny fractures called inclusions. Flawless gemstones are very rare and valuable, and even most high-end gemstones are at least slightly included. Inclusions are nature's way adding variety and individuality to a gemstone.
Cut: Unlike diamonds, with gemstones there isn't an 'ideal' cut geometrically configured for maximum brilliance. But a high-quality gemstone cut is one that presents the most even colour, exposes the fewest inclusions, and displays the majority of the gemstone weight when set in jewellery.
Size: Measured in carats - 1.00ct of gem weight equates to 0.20 grams
Enhancements: Gemstone treatments or enhancements refer to the way some gems are treated to improve their appearance or durability, or even change their colour. Many gemstones are treated in some way. The effects of some treatments may lessen or change over time and some may require special care. Some enhancements also affect the value of a stone, when measured against a comparable untreated stone.
Some common treatments that you may be told about and their effects include:
- Heating can lighten, darken or change the colour of some gems, or improve a gemstone's clarity.
- Irradiation can add more colour to coloured diamonds, certain other gemstones and pearls.
- Impregnating some gems with colourless oils, wax or resins makes a variety of imperfections less visible and can improve the gemstones' appearance and durability.
- Diffusion treatment adds colour to the surface of colourless gems; the center of the stone remains colourless.
- Dying adds colour and improves colour uniformity in some gemstones and pearls.
- Bleaching lightens and whitens cabachon gems including jade and pearls.