Trapiche emerald is a rare variety of the gemstone

emerald Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) ''Gemology'', John Wiley & Sons, New York, p ...

, characterized by a six-pointed radial pattern of ray-like spokes of dark impurities. It is one of several types of trapiche or trapiche-like minerals, which also include trapiche

ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sa ...

sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

chiastolite Chiastolite ( ) is a variety of the mineral andalusite with the chemical composition Al2SiO5. It is noted for distinctive cross-shaped black inclusions of graphite. The presence of the cross caused this mineral be used as a gem. Chiastolite spe ...

and

tourmaline Tourmaline ( ) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is a gemstone and can be found in a wide variety of colors. The ...

. The name comes from the Spanish term ''

trapiche A trapiche is a mill made of wooden rollers used to extract juice from fruit, originally olives, and since the Middle Ages, sugar cane as well. By extension the word is also sometimes applied to the location of the mill, whether the workshop or t ...

'', a sugar mill, because of the resemblance of the pattern to the spokes of a grinding wheel. Trapiche emeralds were first described by

Émile Bertrand Émile Bertrand (1844–1909) was a French mineralogist, in honour of whom bertrandite was named by Alexis Damour. He also gave his name to the ''Bertrand lens'' or phase telescope. He studied at the Ecole des Mines in Paris and was a co-founder ...

in 1879. They are generally only (and rarely) found in the western part of the Eastern Cordillera basin, in the

Muzo Muzo () is a town and municipality in the Western Boyacá Province, part of the department of Boyacá, Colombia. It is widely known as the world capital of emeralds for the mines containing the world's highest quality gems of this type. Muzo ...

, Coscuez and Peñas Blancas mines of Colombia (but likely not in

Chivor Chivor is a town and municipality in the Eastern Boyacá Province, part of the Colombian department of Boyacá. The mean temperature of the village in the Tenza Valley is and Chivor is located at from the department capital Tunja. Economic ac ...

as reported in older literature). Singular finds in Brazil and Madagascar have also been reported. The radial pattern exhibits considerable variance, and often includes a hexagonal structure at the core. There is not yet consensus about the mechanism by which the pattern forms, or the conditions required for it. Various models have been proposed. According to one interpretation the black impurities are remains of the

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

matrix in which the emeralds formed, trapped between the radial

dendrites Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...

of the growing emerald. The trapiche pattern is not an asterism, an optically similar pattern that forms in a different process.

References

{{reflist Beryl group

See also

References