Amethyst

What it actually is

Quartz, silicon dioxide, coloured violet by iron that has been altered by natural radiation in the ground over long periods. Trigonal, hardness 7, no cleavage.

The colour is a defect rather than an ingredient, which explains its two weaknesses. Heat a few hundred degrees and the colour centres break down, turning the stone yellow-orange: that is how most commercial citrine is made. Ultraviolet light does the same slowly and irreversibly, which is why amethyst fades on a sunny windowsill.

Amethyst usually shows colour zoning, with the violet concentrated in bands or at the crystal tips and a paler or white base. Ametrine, which is amethyst and citrine in one crystal, forms where part of a crystal was heated in the ground and part was not.

The best material, sometimes called Siberian grade regardless of origin, shows deep purple with red and blue flashes.

Where it comes from

Amethyst forms in gas bubbles in basalt, which is why the great geodes of Brazil and Uruguay are volcanic. Some of those geodes are large enough to stand inside.

Brazil and Uruguay dominate world supply. Zambia produces fine deep material, Madagascar supplies both specimen and tumbled material, and the Russian Urals were the historic European source that gave rise to the Siberian grade name.

Egypt mined amethyst at Wadi el-Hudi in the Eastern Desert from the Middle Kingdom, working it into scarabs and beads. Minoan and Mycenaean jewellery contains it, and Rome cut it for intaglios in quantity.

The eighteenth and nineteenth-century South American discoveries changed everything. Before them amethyst ranked with diamond, ruby, emerald and sapphire; afterwards it became an affordable ornamental stone, without anything about the material changing at all.

What the traditions claimed

The Greek name amethystos means not drunken, and the belief was practical rather than poetic: amethyst goblets and amulets were used on the theory that one could drink without losing self-command. Pliny records the association and adds protection against poison.

The myth usually told, in which Dionysus is thwarted by a maiden turned to quartz and stains her with wine, is not Greek. It was written by the French poet Remy Belleau in the sixteenth century, which makes it a good example of a modern story circulating as an ancient one.

Christian use is the most durable strand. The amethyst set in a bishop's ring ties the stone to episcopal office in the Western church, and the medieval lapidaries following Marbode give it sobriety, vigilance in prayer and protection against intoxication.

Modern practice attached amethyst to the crown centre of the imported chakra model and made it the standard recommendation for sleep and for calm. That reading is twentieth-century.

How it is worked with

The most common modern use is the bedside stone, and it is a reasonable one for practical reasons as much as symbolic ones: amethyst is cheap, abundant, needs no maintenance, and is pleasant to look at. If a consistent bedtime object helps you keep a routine, that is a real benefit with an ordinary explanation.

For sobriety work specifically, the stone has the longest continuous tradition of any object in the catalogue, running from Greek drinking cups to the bishop's ring. Carrying one as a reminder of a commitment is using it exactly as it has been used for two and a half thousand years.

Amethyst clusters are the common shelf form and geode segments the decorative one. A tumbled pebble is the practical carrying form.

The one rule: keep it out of direct sunlight. A windowsill is the single worst place for it.

Buying it honestly

Amethyst is cheap enough that outright faking is uncommon, but three things are worth knowing.

Synthetic amethyst has been grown hydrothermally since the 1970s and is chemically identical to natural, difficult to identify without instruments. Very even colour with no zoning is a hint towards synthetic, since natural material usually concentrates colour in bands or at the tips.

Dyed purple agate and glass appear at the very cheap end, and the glass test is temperature: quartz stays cool in the hand.

Heat-treated amethyst sold as citrine is the family's main honesty problem, and it runs in the other direction. If you are buying citrine rather than amethyst, look for pale even lemon rather than orange-brown tips over a bleached base.

Prasiolite, the green quartz, is also nearly always heat-treated amethyst.