Boasting the famed colour of royalty, amethyst sets the colour standard for all other purple gemstones. A variety of QUARTZ, amethyst has long been prized and has been included in royal collections from ancient Egypt to the British crown jewels.
Amethyst, like other quartz varieties, is created in many different ways and occurs in many igneous and metamorphic rocks, particularly in granite and gneiss. It is abundant in clastic sediments. It is also a common gauge mineral in mineral veins, and most good crystals are found in this type of occurrence. Some of the best amethyst is found in cavities (geodes) from granite porphyries and pegmatites. Because it resists weathering, amethyst is also found in alluvial sands and gravels.
Amethyst is interesting in that it varies greatly from one location to another, and experts can identify the source mine of a specimen based purely on a visual inspection. For example, while amethyst from Veracruz, eastern Mexico, tends to be very pale and the crystals are usually ‘phantomed’ with clear quartz on the interior and purple on the outside), specimens from Guerrero, southwest-central Mexico, are ‘phantomed’ the other way around and are some of the most valuable amethyst crystals.
The colour of amethyst is unstable and can diminish with protracted exposure to sunlight. Amethyst can also be heat-treated to produce the yellow of the rarer quartz variety, CITRINE. Pale stones may be set in a closed setting with a backing of foil to enhance the colour.
The name amethyst derives from the ancient Greek word amethustos meaning ‘sober’, and it was said that amethyst could prevent the bearer from becoming drunk, which was why wine goblets were sometimes made of the gem. In Greek myth, amethyst was rock crystal dyed purple by the tears of Dionysus, the god of wine and revelry. In fact, it owes its purple colour to impurities of iron.
Today, amethyst is very popular for jewellery. It is found in both long prismatic crystals, which are suitable for cutting, or as druses. Because colour can be patchy, it is often cut as round brilliants to maximize colour. Deep colours are the most valuable.
Amethyst is graded, with the best-quality, darkest specimens judged ‘Siberian’, no matter what their actual source; mid-quality stone are called ‘Uruguayan’ and lesser quality specimens are ‘Bahain’. Pale amethyst is sometimes called ‘Rose de France’. Poor quality stones are often tumbled to make beads or are cut as cabochons.
Sometimes amethyst is part of a mixed crystal: when it alternates with colourless quartz, it is known as amethyst quartz; when it bands with citrine, it is called ametrine.
Today, the best examples of amethyst come from Jalgaon, Maharashtra, western India; Rio Grande do Sol, southern Brazil; and Ratnapura, southwest Sri Lanka. Other sources are variable. In general, South American crystals are larger than African, but the African amethyst has more saturated colour. ‘Uruguayan amethyst’ is famed for flashes of red.
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