Amethyst Quality Factors
The finest amethyst colour is a strong reddish purple or purple with no visible colour zoning. Dealers prefer strongly saturated reddish purple to dark purple, as long as the stone is not so dark that it reduces brightness. If the colour is too dark, an amethyst might look black under dim lighting conditions.
Any brownish or bronze-coloured tints in an amethyst’s purple colour, or any noticeable colour zoning, lower its value dramatically. Buyers of loose amethysts view colour zoning by placing the gems table-down against a white background.
Many amethysts display a weak, light colour or have strong zones of lighter and darker purple colour. These factors lower the value of these stones.
Heat treatment can lighten the colour of very dark amethyst. Lower-quality light-coloured amethyst and even light-coloured quartz have been dyed to impart a purple colour.
Much of the faceted amethyst in the market is eye-clean, meaning it lacks eye-visible inclusions. African material, especially from Zambia, can be a highly saturated raspberry colour. It tends to have more inclusions than Brazilian material. However, due to its remarkable colour, this is considered acceptable in a faceted stone. Eye-clean material of the same colour is more valuable.
Amethysts with eye-visible inclusions but attractive colour are usually cut as cabochons or fashioned into beads. Cabochons and beads that display fine colour and high clarity sell at a substantial premium.
Rarely, amethyst undergoes fracture-filling treatment of its surface-reaching fractures to improve apparent clarity.
Amethyst is cut into a variety of standard shapes and cutting styles. These include rounds, ovals, pears, emerald cuts, triangles, marquises, cushions and others. Facet patterns include the classic triangular and kite-shaped facet arrangements called brilliant cuts, rows of concentric parallel facets called step cuts, and mixed cuts that combine both facet arrangements.
Amethyst is also a very popular gem for cutting into a variety of free-form shapes. This is done by hand or by automated cutting. These so-called fantasy or designer cuts can be mass produced or created as one-of-a-kind pieces. They sometimes display concave faceting, where normally flat facets have a concave shape. Other types of cuts and carvings are also found, including carvings of animals and other objects.
Amethyst is available in all size ranges for setting into a variety of jewellery styles. It’s popular as a large centre stone since the price per carat does not rise dramatically with larger size. Amethyst is also commonly found in calibrated cuts, which means they’re cut precisely to standard industry sizes, in all qualities.