Historically, garnets have played a significant role in the world of gems. They have adorned the necks of high society ranging from Egyptian pharaohs to Victorian-era royalty and beyond.
Pliny the Elder, a famous historian of Ancient Rome, detailed the colour range of garnets in his works from 70 A.D.
Gemmologically, the garnets used as gemstones are a complex family of minerals comprising pyrope, almandine, spessartine, uvarovite, grossular, and andradite.
A single garnet gem is a mix between these different varieties (for example – 50 per cent pyrope, 50 per cent almandine), within limits.
The ability to substitute elements within the structure for other elements of a similar size and nature, in the way garnets do, is known as solid solution.
It is this solid solution characteristic that makes the gemmological constants of garnet more variable than most other gem species.
Garnets occur in all colours and shades except pure blue. The resultant colour of the gem depends on the variable composition (which of the garnet end-members are present).
Pyrope, almandine, and spessartine form a solid solution series together, with varying amounts of each type within one stone. These, particularly almandine and pyrope, are the most commonly occurring. They exhibit a range of brownish, orangish, or purplish red hues and generally comprise the colour range most people associate with garnet.
For garnets of very high spessartine content alongside almandine, colours |can be an eye-catching vivid orange, often referred to in the trade as ‘Fanta orange’.
If the orange colour features a brownish secondary hue, these may be termed ‘mandarin’ in the trade. These gems are rare; found in Bavaria, Italy, Sri Lanka, Madagascar, India, Brazil, and even Broken Hill in NSW.
An intermediate garnet of pyrope and almandine is responsible for the popular Rhodolite variety of garnet, valued for its raspberry, purplish-red hues. Rhodolite garnets are found in Tanzania, East Africa, Sri Lanka, India, and Madagascar.
More recently discovered is another variety of Rhodolite garnet – a deposit in Mozambique produces these garnets with a striking purple hue, much closer to pure in colour (without a strong secondary hue) than the traditional rhodolite garnets.
When spessartine becomes more prominent in the stone along with
pyrope (and varying amounts of almandine and grossular garnet also), the colours produced may parallel that of padparadscha sapphire.
These pale pinkish oranges to deeper orange/pinks, along with hues of a more yellowish orange originate from Tanzania and are known in the trade as Malaia (or Malaya) garnet.
Another variety fresh on the scene is a unique blue-green coloured garnet (a colour never previously seen except in garnets with a strong colour-change), reportedly from the border of Tanzania and Kenya.
In addition to the fantastic warm colours seen in the pyrope-almandine-spessartine garnet series – the addition of chromium and/or vanadium in the gem can also produce a colour-change affect.
Malaia garnets, for example, may produce a slight colour shift to generally more intense colours under incandescent light than in daylight, whilst other, more vanadium-rich pyrope-spessartine garnets can produce a strong colour change from a bluey-green in daylight to a purplish-red under incandescent light.
Overall, gem garnets come in an incredible range of colours and varieties – often unbeknownst to the average jewellery client.
With a hardness ranging from 6.5 to 7.5, they are reasonably scratch resistant, lack cleavage, and are suitable for a range of jewellery designs, provided they are not worn every day.