Tourmaline

Overview

Tourmaline is not one mineral but a group of closely related borosilicates, and it occurs in a wider range of colours than any other gem. A single crystal can change colour along its length or from core to rim, which gives the striking bicolour and "watermelon" (pink core, green rim) stones.

Colour and varieties

• Rubellite: pink to red tourmaline that keeps its colour in both daylight and warm light.
• Indicolite: blue tourmaline, from greenish blue to deep blue.
• Chrome tourmaline: an intense green coloured by chromium and vanadium.
• Paraíba and Paraíba-type: copper-bearing tourmaline in neon blues and greens, first found in Brazil's Paraíba state and later in Nigeria and Mozambique.
• Bicolour and watermelon: several colours in one stone.

Tourmaline is strongly pleochroic: many stones look darker when viewed down the length of the crystal, so cutters orient them carefully.

Key properties

Where tourmaline comes from

Brazil is the classic source. Nigeria, Mozambique, Madagascar, Afghanistan, Namibia, Tanzania, Sri Lanka and the United States (California and Maine) are also important.

Treatments

Heating lightens overly dark green and blue stones; irradiation can intensify pink and red. Some rubellites, which are often included, are clarity enhanced. Copper-bearing tourmaline is commonly heated to improve its blue. Ask for treatments to be disclosed, especially on higher-value stones.

Buying tips

• Judge colour in several lights. Some greens turn olive under warm light; good rubellite stays red-pink.
• Clarity expectations vary by colour. Green and blue stones are usually clean; reds and pinks are naturally more included.
• For Paraíba-type stones, insist on a laboratory report confirming copper and, if claimed, origin.

Care and cleaning

Clean tourmaline with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners and sudden temperature changes. Tourmaline is pyroelectric: it becomes electrically charged when warmed, so it can attract dust in a shop window or a warm room.