Tourmaline belongs to a group of boron silicates with a complex formula that allows wide chemical variation, producing nearly every color. Copper-bearing Paraíba tourmaline displays vivid blue-green. Strong pleochroism causes noticeable color change with viewing direction.
Crystals often show concentric or longitudinal zoning. Hardness ranges 7–7.5; the gem has no cleavage but can be brittle. Many tourmalines are heat-treated to improve color uniformity. Inclusions and growth features aid identification and origin determination.