Amethyst

Amethyst is quartz, the commonest crystal on earth, coloured purple by a trace of iron and the natural radiation of the rocks it grew in. The colour runs from pale lilac to a deep royal purple, sometimes with a cool blue or warm raspberry tint.

For centuries the finest came from Russia, then from Brazil. Today many of the richest purples come from Africa: GIA names Zambia's Kariba mine as a major producer of richly coloured stones. And in the desert mountains of the Brandberg area, north of Swakopmund, Namibia has its own amethyst, prized for crystals that grew in bands of purple, smoky and clear.

Where the name comes from

The name comes from the Greek amethystos, "not drunk". Its wine-like colour linked it with Bacchus, the god of wine, and people believed it kept the wearer clear-headed. The story of the nymph Amethyste, turned to stone and stained by wine, is often told as an ancient myth, but it was written by a French poet in 1576.

Beliefs and legends

• A clear head. Because of its link with wine, people believed amethyst kept its wearer clear-headed and quick-witted, in battle and in business.
• As precious as ruby. Fine amethyst was once valued as highly as ruby, emerald and sapphire.
• A stone of the church and the crown. Amethyst is one of the emblems of the twelve apostles, has long been worn in bishops' rings, and is set in the British coronation regalia.

The colours

• Deep purple: the most valued, especially when the colour is even and has a reddish or royal tone.
• Lilac and lavender: lighter, softer stones, often more affordable.
• Raspberry: the vivid reddish purple of many Zambian stones.
• Green and yellow cousins: heating amethyst can turn it green (prasiolite) or yellow (citrine).

Treatments, honestly

Heating is the most common treatment. It lightens stones that are too dark, and the change is permanent; it cannot darken a pale stone. Some pale quartz is dyed purple, and fracture filling is rare. Synthetic amethyst has been grown since the 1970s and can be hard to tell from natural without laboratory tests, so it must always be disclosed. We tell you what we know about each stone before you buy it.

How to judge an amethyst

• Colour is almost everything. Look for a strong purple or reddish purple, even across the stone. Brown or bronze tints and strong colour banding lower the value sharply.
• Not too dark. A stone that looks black in dim light is less desirable than a slightly lighter one.
• Expect it clean. Most faceted amethyst is clean to the eye.
• Size is affordable. The price per carat barely rises with size, so a large amethyst centre stone is within reach.

Caring for your amethyst

Amethyst is 7 on the Mohs scale and suits everyday wear, though it can scratch if stored with harder gems. Clean it in warm soapy water. Avoid steam, heat and sudden changes of temperature, which can crack it. Some amethyst can fade with long exposure to strong light, so do not leave it in a sunny window.

At a glance

Mineral	Quartz (silicon dioxide), purple variety
Hardness	7 Mohs
Colours	Lilac to deep purple; reddish ("raspberry") or bluish tones
From	Zambia (Kariba); Namibia (Brandberg area); also Brazil, Uruguay
Treatments	Often heated to lighten; rarely dyed; synthetics exist. Disclosed per stone
Care	Warm soapy water. No steam, heat or long strong sunlight