Dark Green Tourmaline

Dark green tourmaline is a deeply saturated green variety of gem tourmaline, usually iron-bearing elbaite (verdelite). The high iron content produces rich, sometimes bottle-green to nearly black colors that lighten to vivid green under strong illumination.

Very dark stones grade chemically toward schorl, and the deepest material can be opaque. Because dark green tourmaline is abundant and affordable, it is one of the most common gem tourmalines in jewelry.

Strong pleochroism is characteristic: looking down the length of a crystal often appears much darker than across it, which cutters must manage.

Dark green tourmaline forms in granitic pegmatites and related hydrothermal environments, where iron is the dominant coloring element. Higher iron content deepens the green and pushes the composition toward the schorl end of the series.

Major sources include Brazil (Minas Gerais), Afghanistan, Pakistan, Madagascar, Namibia, and the United States. The most strongly colored material comes from iron-rich portions of pegmatite systems.

Heat treatment is sometimes used in the trade to lighten overly dark green stones to a more attractive medium green.

Dark green tourmaline shows deep green to blackish-green color, vitreous luster, hardness 7-7.5, very strong pleochroism (often markedly darker along the c-axis), striated prisms, triangular cross-section, no cleavage, and doubling of back facets from high birefringence.

Viewing the stone in bright light and from different directions reveals the green and the pleochroism, separating it from truly black material. Tube and fracture inclusions are common.

Look-alikes include green sapphire, chrome diopside, peridot, and dark emerald; tourmaline's strong pleochroism, birefringence, and habit are diagnostic.

Dark green tourmaline is widely cut for rings, pendants, and earrings, offering rich green color at modest prices; cutters orient stones to avoid an overly dark face-up appearance, and heat treatment may lighten color.

It is also popular as polished crystals and specimens. Metaphysically, green tourmaline is linked to the heart chakra, vitality, abundance, and grounding, traditional associations that are not scientifically verified.