Trapiche emerald
Trapiche emerald is a rare kind of emerald with a distinctive six-arm black pattern that looks like spokes on a wheel, dividing green areas. The pattern can lighten as the stone weathers. It belongs to a family of minerals called trapiche minerals, which also includes trapiche ruby, sapphire, tourmaline, quartz, and chiastolite. The name comes from the Spanish word trapiche, meaning a sugar mill, because the design resembles the spokes of a grinding wheel.
Emerald is a green variety of the mineral beryl, and its color comes from chromium and/or vanadium.
Trapiche emeralds were first described in 1879 by Émile Bertrand. They are extremely rare and are mainly found in Colombia, in the western part of the Eastern Cordillera, particularly at the Muzo, Coscuez, and Peñas Blancas mines. Chivor has been mentioned in older reports, but today it is not considered a likely source. Very rare examples have been found in Brazil and Madagascar.
The radial pattern inside a trapiche emerald can vary. Some cross-sections show a hexagonal core. Scientists don’t all agree on how the pattern forms, and several ideas exist. One theory is that the black arms come from clay minerals in the rock where the emerald grew, which later turned into shale. In a Type A trapiche emerald, these clay minerals form radial dendrites that the emerald layers grow on; a Type B pattern would show the reverse growth.
Trapiche is a fixed-star pattern, meaning it stays in place. It is different from asterism, a moving-star effect seen in some gems due to tiny inclusions or tubes aligned with crystal directions. In rubies and sapphires (corundum), light interacting with such inclusions can create a multi-directional star effect.
This page was last edited on 2 February 2026, at 14:56 (CET).