A genuine gemstone is an item that is rare, beautiful and durable.
Like blind tasting a good wine, when trying to correctly identify a gemstone, be sure not to jump to conclusions based purely on its visual appearance, or you may come unstuck more often than you think.
In identifying different gemstones we look firstly at their colour, hardness, lustre, dispersion and brilliance. If we are still unsure of a gem type, we can accurately measure its refractive index, specific gravity, cleavage, and fracture. Many gemstones display optical characteristics such as asterism, chatoyancy, pleochroism and double refraction, which can also be used to help distinguish one variety from another.
To be classed as a gemstone, a mineral must be beautiful, rare and durable.
Beauty
Beauty is very subjective, but in general the attributes of gems which excite our sense of beauty include colour, transparency, lustre, brilliance, pattern and optical phenomena and, in some cases, distinctive inclusions.
Rarity
There are two types of rarity involved with gemstones: relative and inherent. Relative rarity is when gems occur in many locales and often in large deposits, however, the vast majority of the material is not of gem-quality, therefore this is relative rarity. The mineral Corundum, for example, from which we get precious Ruby and Sapphire, is widespread and abundant, but the amount of gem-quality specimens found are incredibly rare and usually in extremely small pieces. Inherent rarity is when minerals occur in only a few locations or in very small deposits. Alexandrite, Tanzanite and certain Garnets all fall into this category.
There is no scale for rarity in the gemstone industry and with so many gemstones being discovered only in remote, inhospitable areas, there is no way of measuring exactly what quantity of gems are being mined. What we do know is that Diamonds are less rare than you would imagine and other gems such as Alexandrite, Paraiba Tourmaline and Colour Change Sapphires are incredibly rare. Other gemstones such as Tanzanite, Larimar and the recently discovered Astraeolite have to-date only been discovered in one location on the planet, therefore these single source gemstones enjoy a different type of rarity, a rarity I refer to as a “single astronomical geological event” or SAGE for short.
Durability
A gem must be able to withstand the stresses and forces it undertakes to be cut, polished and set into jewellery. It must also be tough and stable enough to be worn every day.
Durability is not just about the hardness (measured by the Mohs scale) of the gem, but also its toughness and crystal structure. In addition to a gem’s natural durability, it is also important to assess if a gemstone’s enhancements are also permanent and durable.
