Trapiche emerald

The name comes from the Spanish term trapiche, a sugar mill, because of the resemblance of the pattern to the spokes of a grinding wheel.

[1] Emerald is a gem variety of the mineral beryl, and owes it distinctive green color to the presence of chromium and/or vanadium.

With few exceptions, they are found in the western part of the Eastern Cordillera basin, in the Muzo, Coscuez, and Peñas Blancas mines of Colombia, where they are rare.

[1] According to one interpretation the black radial arms are developed from clay minerals in the matrix where the emeralds formed.

[2] In the case of corundum (ruby and sapphire), when light strikes the inclusions or nanovoids, it is both reflected and refracted, producing a multidirectional chatoyance.