Tourmaline

Hold a tourmaline up to the window and turn it slowly. The colour shifts as you turn it, deepening down the length of the crystal and softening across it. Some stones carry two or three colours at once. No other gem comes in as wide a range: greens from mint to forest, pinks from blush to raspberry, blues from sea-glass to deep ink.

Tourmaline is also a Namibian stone. The tourmaline we set comes from the Erongo region, about 150 kilometres inland from our shop in Swakopmund, where the granite hills rise out of the desert. When you take one home, you take a small piece of that landscape with you.

Where the name comes from

For centuries, traders mixed tourmaline up with other gems. Green stones were sold as emeralds and red ones as rubies. The name comes from the Sinhalese word toramalli, "mixed gems", which Dutch merchants used for the mixed-colour gem pebbles they brought from Sri Lanka. It suits a gem that has always been hard to pin down.

Beliefs and legends

For two thousand years, writers repeated a strange tale about a stone that pulled straw and small pieces of wood towards it. The Greek philosopher Theophrastus said it formed from the urine of the lynx, and Pliny the Elder copied the story three centuries later. The stone was almost certainly tourmaline.

When Dutch traders brought tourmaline from Ceylon, now Sri Lanka, around 1703, they found it drew the ashes out of warm coals. The secret is real, and nothing to do with lynxes: warm a tourmaline crystal and it becomes electrically charged, with opposite charges at its two ends.

Where it forms

Tourmaline grows in pegmatites: pockets of slow-cooling granite where rare elements such as boron gather and have time to build large crystals. The crystals are long and ridged, with a rounded, triangular cross-section, and many change colour along their length as the chemistry of the pocket changed while they grew.

The colours, and their names

• Green (sometimes called verdelite): the most familiar tourmaline. Fine greens hold their colour in daylight and under shop lights.
• Pink to red (rubellite, for the strongest reds): prized when the colour stays the same in every light.
• Blue (indicolite): rarer, and highly valued when it is not too dark.
• Watermelon: a slice across a crystal with a pink centre and a green rim, sometimes with a white band between. Each slice is unique, which makes it a favourite for one-of-a-kind pieces.
• Bi-colour and tri-colour: one stone cut to show two or three colours side by side.

Treatments, honestly

Many tourmalines are sold exactly as they come from the ground. Some green and blue stones are gently heated to brighten or lighten their colour, and some pink stones are irradiated to deepen theirs. Both changes are permanent and widely accepted in the trade. Namibian tourmaline is often untreated, but "often" is not a promise: we tell you what we know about each stone before you buy it.

How to judge a tourmaline

• Colour comes first. Look for colour that is lively and even, not too dark and not washed out. Turn the stone: a good cutter orients the crystal so the best colour shows through the top.
• Expect some inclusions in pinks and reds. Green and blue tourmalines are usually clean to the eye. Pink and red stones naturally grow with more inclusions, and a few are part of their character.
• Watch the dark angle. Tourmaline looks darker along the length of the crystal than across it. In a well-cut stone you should not see a black "window" when you look straight down.
• Size and rarity set the price. Clean, bright reds and blues are the rarest colours. Large stones in those colours are expensive anywhere in the world.

Caring for your tourmaline

Tourmaline is hard enough for everyday rings and pendants (7 to 7.5 on the Mohs scale). Clean it in warm water with a little mild soap and a soft brush, especially behind the stone where dirt collects. Avoid home ultrasonic cleaners, which can crack included stones, and keep it away from sudden heat. One curiosity: when tourmaline is warmed it becomes slightly electrically charged, a property scientists have studied for centuries.

At a glance

Mineral group	Tourmaline (boron silicate)
Hardness	7 – 7.5 Mohs
Colours	Green, pink, red, blue, watermelon, bi-colour
From	The Erongo region, Namibia
Treatments	Often none; some green/blue heated, some pink irradiated. Disclosed per stone
Care	Warm soapy water, soft brush. No ultrasonic, no sudden heat