Trapiche emeralds are a rare variety of emerald that exhibit a six-sided, zoned morphology. Inclusions of their black shale matrix separate the growth sectors of the crystal. (See accompanying photo.) A cross-section through the trapiche crystals, cut perpendicular to the c-axis of their central core, resembles a wheel with six spokes.

Trapiche emeralds are occasionally found in a few mines on the west flank of the Eastern Cordillera Basin of Colombia. They are thought to form when fluid overpressuring, followed by sudden decompression, causes rapid crystallization of emerald. During this rapid crystal growth, particles of the black shale matrix are trapped between the six growth sectors of the emerald crystals. This is the origin of the six black spokes of the wheel.