Colour
Like colourless diamonds, the quality of a coloured gemstone is determined by a combination of the 4Cs: colour, clarity, cut and carat weight. For coloured gems, however, colour is by far the most important factor. In some cases, such as whether a gem is called pink sapphire or ruby, or green beryl or emerald, the distinction may be made based on colour alone. Clarity is important, but for most coloured gems there is no universal grading system or set of standards to evaluate clarity. And cut may vary greatly from stone to stone. The goal is typically to maximize size and colour – or, as in the case of fantasy cuts, to create a custom-made engagement ring that is a work of art.
Durability
Durability is a major consideration when searching for a quality engagement ring gemstone. The gem you choose must withstand the bumps and bangs of daily wear, plus the effects of heat, light, household chemicals and low or high humidity. Different gemstones have different properties and, as a result, different tolerances to these stressors.