Indicolite

Indicolite is the blue variety of tourmaline, a complex borosilicate mineral in the tourmaline group. The blue color is typically caused by trace amounts of copper within the crystal lattice, usually in the elbaite species. The hue ranges from pale blue to vivid electric blue and blue-green, and color zoning or zoning can occur within a single crystal.

Indicolite crystals form in granitic and pegmatitic rocks and are found worldwide, with recognized deposits in Brazil, Afghanistan, Madagascar, Nigeria, Mozambique, and Tanzania, among others. In gemology, indicolite is valued for its vibrant color and is cut for jewelry as faceted stones, cabochons, or composite pieces. It is commonly treated only rarely; natural blue tourmaline is relatively stable, though heat and irradiation can alter color in some stones.

Chemically and structurally, tourmaline has the general formula XY3Z6O18(BO3)3Si6O18(OH)4, and indicolite refers to blueish hues within the elbaite subgroup. The stones typically have hardness around 7 to 7.5 on the Mohs scale, no true cleavage, and a specific gravity around 3.0–3.2. They exhibit strong pleochroism, appearing blue on one crystallographic axis and greenish-blue or colorless on the other, and show a range of transparency from transparent to translucent.

The name indicolite is used in the trade to denote blue tourmaline varieties, especially those colored by copper, distinguishing them from other tourmaline colors and from neon blue types such as paraiba tourmaline.