The name garnet comes from the Latin word granatus or granum meaning “seed”, as red garnet in its rough state is similar in colour and shape to the seed of the pomegranate.
Garnet has a long history of use as a decorative as well as a practical item. Its hardness of 6.5 to 7.5 on the Mohs scale, durability and vibrant colour palette make it ideal for use in jewellery as well as a range of ceremonial regalia such as crowns, chalices and sceptres.
Hardness and durability, key properties valued by jewellers and artisans for millennia, also make garnet an ideal modern industrial resource. Originating in volcanic and metamorphic environments and thus subjected to extreme heat and pressure, garnet can withstand similar extremes in an industrial setting.
Today, industrial grade garnet is widely used as an abrasive, in high-pressure water jet cutting tools, as a component of wear resistant road paints and in rechargeable batteries. Australia is a leading supplier of industrial grade garnet, with mines in Western Australia and the Northern Territory.
Gem quality garnet is typically viewed as a red gemstone, with colour variations of brownish red to reddish pink. However, this is only one part of the gem’s colour story.
Many customers are surprised to learn that this affordable gemstone comes in a rainbow of hues, including colourless, blue, black, orange and yellow, purple and a range of greens. There is also a colour change garnet, which shows blue-green in daylight, shifting to purple-red under incandescent light.
Why does garnet have so many colours? The answer relates to chemical processes as the garnet crystal is forming. Simply put – because the chemistry of the garnet family is complex – in some garnets, oxides of metals such as iron, chromium and magnesium are inherent to the crystal, thus creating specific colours.
In other garnets, trace elements are included as the gem form, thus creating a different range of colours.
The garnet family is an extensive one, with 20 members. In the jewellery world, five members are of importance, namely: pyrope, almandine, spessartine, grossular and andradite. Each of these will be considered next month in Part II of the Garnet – Gem Of Many Colours series.
Colour aside, garnet can also display the rare optical effects of chatoyancy (cat’s-eye effect) and asterism (star effect). Such garnets are highly sought after. Some garnets may also contain iron, giving these gems magnetic properties. In addition to its colour range, garnet has a bright vitreous lustre.
One garnet type, the vibrant green demantoid, has a dispersion value greater than diamond, adding to this garnet’s gemmological and jewellery value.
Gem quality garnets are found across the world, including in Brazil, Australia, Myanmar, Madagascar, India, Sri Lanka and Namibia.