Blue tourmaline is a variety of tourmaline whose colour ranges from soft blue to deep, rich blue. It is also known as indicolite. Its colour comes from traces of iron in its crystal structure. With a hardness of 7–7.5 on the Mohs scale, it offers good durability. It is one of the rarest varieties of tourmaline in the world.

Indicolite is the official gemological name for blue tourmaline. The term derives from the word "indigo" and covers the full range of blue tourmaline shades. Indicolite spans from bright, luminous light blue to intense deep blue. Some indicolites display green undertones, tending towards blue-green. It is one of the most sought-after tourmaline varieties among collectors.

Both stones can display similar blues, but their chemical composition differs. Sapphire is a corundum (aluminium oxide) with a hardness of 9. Tourmaline is a complex silicate with a hardness of 7–7.5. Sapphire offers greater resistance for intensive daily wear. Blue tourmaline presents a softer, more velvety brilliance. In terms of price, a blue tourmaline typically costs five to ten times less than an equivalent blue sapphire.

The price of a blue tourmaline varies according to colour saturation and carat weight. For a good-quality blue tourmaline of around 1 carat, expect to pay €300 to €800 per carat. For 2–3 carats of equivalent quality, prices range from €800 to €2,000 per carat. Exceptional indicolites with deep, pure blue colour and no inclusions can reach €3,000 to €5,000 per carat. Paraíba tourmalines far exceed these ranges, from €5,000 to €50,000 per carat.

Blue tourmalines come primarily from four historic sources. Brazil (Minas Gerais) has been the benchmark since the eighteenth century. Madagascar has established itself as the world's second major source since the 1990s. Afghanistan (Nuristan) produces exceptional indicolites. Pakistan rounds out the offering with deep, rich blues.

Blue tourmaline is sometimes subject to low-temperature heating to intensify its colour. This treatment is internationally accepted and stable over time. Unheated indicolites command a premium over treated stones of equivalent quality. Bonnot Paris favours natural blue tourmalines. The independent certificate systematically specifies any treatment the stone may have undergone.

Yes, blue tourmaline is suitable for an engagement ring, with a few considerations. Its hardness of 7–7.5 makes it less resistant than blue sapphire (9). A protective setting is recommended for intensive daily wear. It offers an original and more accessible alternative to the classic blue sapphire. Its unique colour makes it a bold and refined choice.

Paraíba tourmaline is a variety of blue tourmaline coloured by copper. Its neon blue-green colour — often described as "electric blue" — sets it radically apart from classic indicolites. Discovered in Brazil in the 1980s, it ranks among the most expensive gemstones in the world. Its price regularly exceeds €20,000 per carat for the finest qualities. Indicolite (classic blue tourmaline) offers softer, more understated blues at a far more accessible price.