A bicolour tourmaline is a variety of tourmaline that displays two distinct colours within a single stone. This characteristic arises from chemical variations during crystal growth. The stone may show sharply defined colour zones or soft, gradual transitions. Every bicolour tourmaline is therefore unique. The most sought-after combinations pair pink with green, blue with green, or pink with orange.

A watermelon tourmaline is a bicolour tourmaline with a pink core and a green border, recalling the flesh and rind of a watermelon. It is the most celebrated variety of bicolour tourmaline. A slice cut perpendicular to the crystal perfectly reveals the characteristic pattern. Exceptional watermelon tourmalines display a sharp, clean contrast between the two colours with no blurred transition. The finest specimens come from Brazil and Madagascar.

The colour of a tourmaline depends on the trace elements present in its crystal structure. As the crystal grows, these elements can shift significantly. The stone then develops zones of differing composition, each producing its own hue. Manganese gives rise to pink, while chromium and vanadium produce green. This variation creates the characteristic bicolour effect.

Bicolour tourmalines come primarily from four origins. Brazil (Minas Gerais) has been the historic benchmark since the 18th century. Madagascar has established itself as the world's second major source since the 1990s. Afghanistan (Nuristan) produces exceptional bicolour tourmalines. Nigeria and Mozambique round out the supply with varied production.

Price varies according to the colour combination, the contrast and the carat weight. Expect to pay €200 to €800 per carat for a good-quality bicolour tourmaline of around one carat. Gem-quality watermelon tourmalines reach €800 to €2,500 per carat. Exceptional stones with perfect contrast can exceed €5,000 per carat. The uniqueness of each stone has a strong bearing on the final price.

Most bicolour tourmalines are sold in their natural state. A proportion, however, undergo low-temperature heating to intensify their colours. This treatment is stable and internationally accepted. Unheated bicolour tourmalines command a higher price. Bonnot Paris favours natural stones. The independent certificate always specifies any treatment that may have been applied.

Yes — it is a bold and singular choice for an engagement ring. Bicolour tourmaline has a hardness of 7–7.5 on the Mohs scale, sufficient for attentive daily wear. Its dual tone evokes union, duality and complementarity — a powerful symbol for a marriage proposal. Since every stone is unique, your ring will be too.

The choice of cut is key to showcasing a bicolour tourmaline. A rectangular emerald cut highlights the chromatic zoning to perfection. Watermelon tourmalines are often cut into slices to reveal the characteristic pattern. An oval cut brings out the depth of the two hues. For the setting, yellow gold and rose gold create a warm chromatic dialogue, while white gold offers a more neutral reading of the colours.