A bi-colour tourmaline crystal shows two distinct colour zones along its length or across its cross section, most often a green and pink combination, though other pairings occur.
The effect comes from the same process behind watermelon tourmaline's banding. As the crystal grows, the chemistry of the fluid it forms from shifts, and the trace elements being incorporated change with it. A crystal that starts growing in manganese rich conditions and finishes in iron rich conditions will show pink transitioning to green, or the reverse, depending on which end grew first.
Afghanistan's pegmatite fields are one of the world's most productive sources of bi-colour tourmaline, and material from mining areas such as Paprok and Pech is well known among collectors for its clarity and saturated colour.
Bi-colour crystals are collected both as natural, untouched specimens and cut into gemstones, where a skilled lapidary can orient the cut to show both colours in the finished stone.
See the full range in our Bi-Colour Tourmaline collection.