Packing a punch at the top of the purple gemstone list is amethyst from the quartz family; it’s popular, plentiful and affordable.
The finest amethyst colour is strongly saturated bluish-purple with red flashes that is typical of top-quality Brazilian and Zambian material, although tones from lavender to near colourless are also available.
Fluorite, a much softer gemstone, may also occur in these hues. Synthetic amethyst is abundant and sometimes requires laboratory analysis to be identified.
Amethyst is often confused with a trio of other gemstones – sapphire, tanzanite and iolite. Sapphire is durable, valuable, comes from the corundum family and ranges from purple to lavender to violet.
Medium-violet to bluish-violet tanzanite is softer than sapphire; however, its abundance and price make it an attractive alternative.
Iolite, from the cordierite family, may be confused with tanzanite due to a shared property called trichroism – where three different colours are observed from different directions. The trichroic colours, however, are different for each gemstone, which allows for separation.
The purple posse continues with tourmaline and zircon. Tourmaline has a glass-like lustre and doubling of the back facets, whereas zircon has a diamond-like lustre.
Next up is purple diamond. Pure purple hues are extremely rare, and thus stones are more commonly seen with a secondary modifier such as blue, grey or brown.
A less expensive alternative is irradiated diamond or coated, white diamond.
Less exotic but more accessible is purple or ‘grape’ garnet, a high-quality purple-red to cranberry rhodolite garnet from India that is a mixture of pyrope and almandine varieties.
Two uncommon natural gemstones that could be mistaken for amethyst are scapolite and spinel. Scapolite varies from lavender to violet but it is much softer and strongly pleochroic. Spinel is available in a stunning array of violet, lavender and purple hues varying in intensity.
Kunzite – from the spodumene family – and spinel may occur in a similar light-toned lavender; however, the former is separated by its strong pleochroism. Kunzite may be irradiated to intensify the purple colour.
Taaffeite, a rare collectors’ gemstone, was initially misidentified as spinel due to its pale mauve colour and overlapping properties.
For a different twist on a purple gemstone, there are ‘composites’ composed of two or three different components that are intended as imitations. For example, a sapphire doublet has a natural corundum crown and a purple glass or synthetic sapphire pavilion, while a garnet-topped-doublet has a garnet crown fused to a purple glass pavilion.
Common imitators and synthetics of purple gemstones include glass, synthetic cubic zirconia, gadolinium gallium garnet (GGG), yttrium aluminium garnet (YAG), synthetic sapphire and synthetic alexandrite. Less common are apatite, alexandrite, imperial topaz and benitoite.
This list is just the beginning; there are many more amazing and beautiful purple gemstones for you to discover. Trust your local gemmologist or registered NCJV valuer to separate and identify them for you.