Tourmaline Gemstones – Properties, Origins, Treatments and Buying Guide

Tourmaline is one of the most diverse and colourful gemstones, prized for its wide range of hues, excellent clarity, and strong brilliance. Unlike stones with uniform colours, tourmaline is celebrated for its striking colour variety, from deep greens to vivid pinks, blues, and bi-coloured forms.

In this guide we examine tourmaline from a professional gemmological and commercial perspective, covering its physical properties, crystal system, treatments, origins and how to identify fine-quality stones.

Tourmaline is a boron silicate mineral with complex composition, forming elongated prismatic crystals. It occurs in granites, pegmatites, and metamorphic rocks. Tourmaline’s exceptional colour diversity, clarity, and durability make it highly sought after for fine jewellery and collector specimens.

Tourmaline has the general chemical formula:

XY₃Z₆(BO₃)₃Si₆O₁₈(OH)₄

Where:
X = Na, Ca, K
Y = Li, Mg, Fe, Mn, Al
Z = Al, Mg, Fe

This complex composition explains the wide range of colours and optical effects seen in tourmaline crystals.

Tourmaline belongs to the silicate mineral family, specifically the cyclosilicates. Its crystal system is trigonal, forming long prismatic crystals with characteristic striations along the length, contributing to its optical brilliance.

Tourmaline combines excellent transparency, high refractive index, and vibrant colour, making it ideal for fine jewellery and collectors.

Lustre
Vitreous, providing strong brilliance.

Transparency
Transparent to translucent; gem-quality stones are usually fully transparent.

Refractive index
1.614 – 1.666, giving strong brilliance and sparkle.

Specific gravity
3.06 – 3.25, typical of medium-density silicate gemstones.

Tourmaline exhibits a wide colour palette:

Green
Pink
Red (rubellite)
Blue
Yellow
Brown
Bi-coloured and parti-coloured varieties

The most valuable stones are intensely coloured with minimal zoning.

Tourmaline has a Mohs hardness of 7 – 7.5, making it suitable for all types of jewellery including rings, pendants, and earrings. It has good toughness but can be cleaved along crystal planes if struck sharply.

Most tourmaline is untreated. Some stones undergo heat treatment to enhance pink or red colours. No coatings or fracture fillings are standard for fine-quality gemstones.

Avoid harsh chemicals and sudden temperature changes.
Clean with warm water, mild soap, and a soft brush.
Store tourmaline separately from harder stones to prevent scratches.

Major sources of tourmaline include:

Brazil
Afghanistan
Madagascar
Nigeria
Pakistan
Mozambique
United States (California, Maine)
Sri Lanka