Indicolite

Indicolite is the blue variety of tourmaline, colored primarily by iron (Fe²⁺) in the crystal structure. The blue is produced when iron occupies specific crystallographic sites within the complex tourmaline structure, allowing it to absorb red and yellow light.

Like other elbaite tourmalines, indicolite forms in lithium-rich granitic pegmatites. The combination of lithium, boron, aluminum, iron, and other elements must be present in the right proportions and at the right temperature for blue tourmaline to crystallize. This specificity makes true blue tourmaline less common than green or pink varieties.

Pure blue indicolite (without green overtones) is particularly rare and valuable. Most blue tourmaline has at least some teal or greenish component. Heat treatment can sometimes reduce the green component, shifting blue-green tourmaline toward a purer blue.

Indicolite is identified by its blue to teal-blue color within the tourmaline crystal habit: elongated striated prisms with rounded triangular cross-section. Strong pleochroism shows different intensities of blue from different angles.

Distinguish from blue sapphire (higher RI, different crystal system), blue topaz (orthorhombic, different properties), aquamarine (hexagonal, lighter blue), and blue apatite (softer). The triangular cross-section and strong dichroism are key tourmaline identifiers.