The Gachala Emerald is an 858-carat rough emerald crystal recovered from the Vega de San Juan mine in the Gachala municipality of Cundinamarca, Colombia, in 1967. The crystal is one of the largest and finest emerald crystals ever recovered from any source and is held in the Smithsonian Institution's National Gem Collection in Washington, D.C., where it has been on continuous public display since its donation by Harry Winston in 1969.

Discovery

Gachala lies in the eastern emerald belt of Colombia, approximately 80 miles northeast of Bogota in the Cordillera Oriental. The Gachala mining district has produced emerald commercially since at least the early twentieth century, although the area is associated with pre-Hispanic Muisca emerald sources of considerable antiquity. The Vega de San Juan mine is one of the principal underground operations in the district, working hydrothermal calcite veins in carbonaceous black shale of Cretaceous age. The geology of the Gachala emeralds, like that of the better-known Muzo and Chivor sources, is unusual in that emerald is hosted in sedimentary rather than igneous or pegmatitic rock, and the colouration is from chromium and vanadium derived from the host shales.

The Gachala Emerald was recovered in 1967 from a vein in the mine. Trade accounts of the recovery describe a hexagonal prismatic crystal of remarkable clarity and saturation, weighing 858 carats and measuring approximately 5 centimetres in length. Photographs and gemological examinations of the crystal show the typical Colombian three-phase inclusions (gas, liquid, and solid in the same cavity) characteristic of hydrothermal emerald, distributed unevenly through the crystal but leaving large clean regions.

Acquisition by Winston

Harry Winston, the New York gem dealer and donor whose firm had also handled the Hope Diamond, acquired the Gachala Emerald shortly after its recovery. Winston's strategy with major rough crystals was generally to study the rough for cutting potential before deciding whether to cut, sell rough, or hold for donation. In the case of the Gachala, Winston elected to retain the crystal in rough form on the grounds that the size and quality of the crystal made it more important as a specimen than as cut goods.

Winston donated the crystal to the Smithsonian in 1969. The donation followed the same pattern as the Hope donation a decade earlier: an unconditional gift to the public collection, with the donor identified in the museum label. The gift consolidated the position of the Smithsonian as the principal public destination in the United States for major coloured stones and historical diamonds.

Display and significance

The Gachala Emerald is displayed in the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals at the Smithsonian's National Museum of Natural History. It sits alongside other major Colombian specimens including the Hooker Emerald (a 75.47-carat cut emerald set as a brooch) and various smaller crystals from Muzo and Chivor. The display context emphasises the geological and gemological significance of the rough crystal as a study specimen.

For the trade, the Gachala Emerald is significant for several reasons. It is, with a small number of other comparable specimens, evidence of the upper limit of crystal size and quality that the Colombian emerald deposits produce. It serves as a reference for the typical inclusion pattern and colour of Gachala material as distinct from Muzo or Chivor material. The Gachala output, broadly speaking, runs slightly more bluish-green than Muzo, which tends to a slightly more yellow-green saturation, although these distinctions blur considerably across individual stones and are not reliable origin determinants on their own.

Comparisons

Several other large Colombian rough crystals have appeared in the historical record. The Patricia Emerald, an 632-carat rough crystal from Chivor recovered in 1920, is held by the American Museum of Natural History in New York. The Mogul Emerald, a 217-carat carved Mughal emerald with Persian inscriptions dated 1107 AH (1695 to 1696 CE), passed at Christie's in 2001 for 2.2 million dollars and is in private hands. The Bahia Emerald, a 752-pound emerald-bearing matrix specimen from Brazil rather than Colombia, is the subject of long-running litigation and has not been on public display.

The Gachala remains, on size and quality combined, in the top tier of recorded Colombian rough emerald specimens. The fact that it has been held in a public collection for over fifty years rather than cut or dispersed is itself unusual in the history of major emerald rough, and reflects the donation philosophy that Winston brought to several major specimens at the end of his career.