Origin of name
The 858-carat "Gachala Emerald" described as one of the most beautiful
emerald gemstones ever known, gets its name from the mining district where
the "Vegas de San Juan" mine that produced the renowned gemstone was
situated. Though lighter in color the Gachala emeralds were cleaner with
less inclusions and more transparent than emeralds produced in other regions
of Colombia, such as Muzo, Cosquez, and Chivor. Besides the "Gachala
Emerald," the Gachala emerald mines have also produced some spectacular
gemstones, such as 7,025-carat "Emilia Emerald" and the massive 16,020-carat
"El Monstro Emerald." The Gachala emerald mining district is situated east
of Bogota, the capital city of Colombia, at the southeastern end of the
NW-SE emerald belt, in the "Cordillera Oriental" region of the Colombian
Andes Mountain. Unlike the Muzo, Chivor and Cosquez mines which have a
recorded history dating back to the 16th century, to the Spanish
colonization of South America, or according to archaeological evidence
perhaps to the 10th century B. C. to the beginnings of one of the earliest
human civilizations of the Muisca people, the Gachala emerald mines are of
contemporary origin discovered only in 1956.
Image above is
under creative
commons license
Characteristics of the gemstone
One of the largest gem-quality emerald
crystals in the world
The "Gachala Emerald" is a hexagonal short prism, conforming to the
normal crystal habit of emeralds and having a
height of 5 cm and a diameter of almost the same length. The hexagonal shape
of the crystal is more evident at upper end of the crystal, but it is not a
regular hexagon, with two opposite sides of the hexagon shorter than the
other four sides. The six sides of the crystal can be identified even on the
sides of the crystal, even though the crystal looks more cubical than
hexagonal from the sides. The color of the crystal is a pure deep green, and
the crystal appears to be opaque. Unless the crystal is polished we may not
be able to say anything about the diaphaneity of the gemstone. But, it is
well known that most of the Gachala emeralds have good transparency and
shine with increased brilliance. The "Gachala Emerald" is one of the largest
gem-quality emerald crystals in the world.
Composition, structure and color of emeralds
Emeralds which are beryls, belong to the sub-class cyclosilicates of the
main class of minerals called silicates, the predominant class of minerals
found on the earth's surface. In cyclosilicates six tetrahedral silicate
ions (SiO4)‾
are linked together, after the elimination of an
oxygen atom, to form a regular hexagonal ring [(SiO3)6]‾
with an overall negative charge of 12, which is balanced by the 12 positive
charges on two Al3+ ions and three Be2+ ions , that hold the rings together
in the crystal structure, giving an overall chemical formula of Be3Al2(SiO3)6
The regular hexagonal shape of the ring is usually reflected in the final
crystal habit of emerald, which is also hexagonal.
Pure beryl is colorless, but if some of the aluminum
atoms in the crystal are replaced by chromium and/or vanadium atoms, a green
color is imparted to the crystals, known as emerald. Chromium atoms alone or
when chromium predominates over vanadium a deep vivid green color is
produced, as in the case of the Gachala emerald. But if significant
quantities of vanadium is also found together with chromium, a bluish green
color is produced as the emeralds of the Chivor mines and the Zimbabwean
emeralds.
Characteristic features of
emeralds
The characteristic features of emeralds include the following :-
1)The presence of inclusions - The presence of
cracks, fissures and other inclusions is a characteristic feature of all
naturally occurring emeralds, signifying their turbulent genesis, in
hydrothermal veins, pegmatites and contact zones of igneous intrusions into
the surrounding aluminous schist, shale or limestone. The presence of three
phase inclusions, solid, liquid and gaseous, is typical of Colombian
emeralds. Some of the solid inclusions found in emeralds are calcite,
parisite, pyrite, albite, tremolite, tourmaline and biotite. The type of
inclusions seem to vary with the source of the emerald.
The presence of flaws and inclusions had necessitated attempts to reduce
their appearance in the crystal, by oil treatment, which is generally
accepted in the trade. The oil used should have a refractive index
comparable to the emerald, to render the cracks and fissures invisible. Such
an oil is cedarwood oil.
2) Fragility of emeralds - In spite of the good hardness of emeralds which
is 7.5 to 8.0 on the Mohs scale, emeralds are somewhat fragile - a character
imparted by the presence of flaws and inclusions - and therefore difficult
to work with. The rectangular or square shaped step-cut with beveled
corners, known as the emerald-cut, specially developed for emeralds, reduces
the mechanical strain on the crystal, while at the same time bringing out
the intrinsic beauty of the stone.
3) Low specific gravity - The specific gravity of emeralds is low and varies
between 2.67 to 2.78. The specific gravity seem to vary with the source of the
emerald.
4) Low refractive index - The refractive index of emerald is also quite low
and varies between 1.565 and 1.599. It also varies with the source of the
emerald.
5) Low dispersion - Emeralds have a low dispersion of 0.014. The low
dispersion, and refractive index of emerald reduces the "fire" of the stone,
but this is compensated to some extent by the vitreous luster, the vivid
green color, transparency, and the special emerald-cut of the gemstones.
6) Distinct dichroism - Emeralds have a distinct dichroism, changing from
blue-green to yellow-green.
7) Lack of fluorescence in u-v light - Natural emeralds do not fluoresce in
ultra-violet light, and sometimes show a very weak orange-red or green
fluorescence.
Special features of Gachala emeralds
Gachala emeralds are generally cleaner, with less flaws and inclusions than
emeralds from other mines in Colombia, such as Muzo, Coscuez and Chivor. The
emeralds are generally "eye clean" with good clarity, transparency and
brightness. However, their color is generally pale green. In emeralds color
is a crucial factor that determines their value, the darker vivid green
colors, in spite of the presence of inclusions, commanding the highest
prices as compared to the pale green but much cleaner stones. Unfortunately
in emeralds the best green colors seem to be the most included.
History of the Gachala Emerald
Source of the emerald
The source of the "Gachala Emerald" was the "Las Vegas de San Juan" mine,
situated in the Gachala mining district, of Cundinimarca Province, of
Colombia. The "Gachala Emerald" was discovered in the year 1967.
The Gachala emerald deposits were discovered in the year 1954, when an
emerald was discovered in the "Las Vegas de San Juan" area. An immediate
rush by illegal prospectors (guaqueros) to the area led to the discovery and
disappearance of large quantities of fine stones, before the intervention of
the government to open up the area for legal mining.
Almost all the known emerald deposits of Colombia lie in a
northwest-southeast (NW-SE) belt running across the Andes mountain range,
also known as the "Cordillera Oriental," on the northern and eastern side of
the capital city of Bogotá. Muzo, Coscuez and Pena Blanca emerald mines lie
at the northwestern end of this belt, and Gachala, Chivor and Guateque lie
at the southeastern end. The Nemecon, Chirvaneque, and Raquira-Tinjaca
emerald mines, lie almost on a line northeast of Bogotá, somewhere in the
middle of the belt. Some geologists refer to the mines situated towards the
northwestern end of the belt as the western emerald belt and the mines
situated at the southeastern end of the belt as the eastern emerald belt.
The western emerald belt is sometimes referred to as the Vasquez-Yacopi
mining district and the eastern emerald belt as the Guavio-Guateque mining
district.
The mines of the Vasquez-Yacopi mining district are :- the Muzo mine at Muzo,
the Cosquez mine at Muzo, La Glorieta mine at Yacopi, Cunas mine at Maripi,
and Polveros mine at Maripi.
The mines of the Guavio-Guateque mining district are :- Chivor mine at
Chivor, the Gachala mine at Gachala, the Matacana mine at Gachala, and the
Macanal mine at Macanal.
In the Guavio-Guateque mining district, where the Chivor and Gachala mines
are situated the rocks are mainly shale and sandstone, and emerald crystals
are found in veins containing pyrite, quartz and albite. Recent geological
and palaeontological studies conducted by the Center for Petrographic and
Geochemical Research, in the Gachala region, have shown that the emerald
deposits are at least 65 million years old arising from a much older (135
million years) Lower Cretaceous fossiliferous sedimentary bed bearing
cavities left by the dissolution of the calcareous shells of fossilized
gastropods. The hot mineralizing fluids from the magma flowed into the
sedimentary rocks filling the fractures, shear zones, faults and
particularly cavities left by the dissolution of the fossilized gastropod
shells, which subsequently precipitated to form emerald crystals.
The Gachala Emerald is purchased by Harry
Winston
The "Gachala Emerald" that was discovered in 1967 in the "Vegas de San Juan"
mine in the Gachala district, was purchased by Harry Winston, the New York
based jeweler and diamond dealer, who later donated the rare crystal to the
National Museum of Natural History of the Smithsonian Institution. Harry
Winston had in November 1958, donated the infamous 45.52-carat, fancy dark
grayish blue "Hope Diamond" to the Smithsonian Institution, after owning it
for nearly 10 years since be purchased it in 1949. The curse of the "Hope
Diamond" that had adversely affected so many previous owners had apparently
not affected Harry Winston, even though he held the diamond for almost a
decade. In fact his business prospered and expanded after he purchased the
"Hope Diamond," and he lived up to the ripe old age of 82 years, and died
only in December 1978 of a natural cause, a heart attack. In the
year 1963, the Smithsonian Institution had acquired the 127.02-carat,
colorless "Portuguese Diamond" from Harry Winston in exchange for 2,400
carats of small diamonds.
Harry Winston, who set up the renowned Harry Winston Diamond Corporation,
which operates seven salons in the United States and ten salons in other
countries, was not only a "King of Jewelers" but also a "Jeweler to Kings"
and royal families around the world. Besides being a skilled jewelry
designer, Harry Winston also designed crowns and tiaras for the royalty
around the world. Harry Winston was responsible for designing Empress Farah
Diba's tiara on the occasion of her marriage to Shah Mohammed Reza Pahlavi
held in 1958, and also the "Farah's Favorite Tiara" made out of emeralds and
diamonds, which she wore on formal occasions, such as during her husband's
official visit to the United States and Canada in 1965.
During his lifetime as a jeweler, around 30 famous diamonds had passed
through his hands, which are now found in collections around the world, both
museum as well as private collections. Some of these diamonds are the Idol's
Eye, the Indore Pears, the Jonker, the Liberator, the Lesotho, the Nassak,
the Niarchos etc.
The Gachala Emerald is exhibited at the
Smithsonian's NMNH
The "Gachala Emerald" is now exhibited as part of the National Gem
Collection, in the Janet, Annenberg Hooker Hall of Geology, Gems and
Minerals, of the Smithsonian's National Museum of Natural History, together
with other famous emeralds such as the Mackay Emerald Necklace, the Hooker
Emerald Brooch, Chalk Emerald Ring, Maximilian Emerald Ring, the Spanish
Inquisition Necklace and other more famous exhibits such as the Hope
Diamond, the Portuguese Diamond etc.
The Gachala Emerald exhibited at the Tucson
Show of February 2003
The "Gachala Emerald" was exhibited at the 49th Tucson Gem & Mineral Society
show held in February 2003. The show that was held between February 13th to
17th, opened with an evening reception and talk by Michael Scott, former
president of Apple Computer Company, who is also a collector and connoisseur
of gemstones and minerals. The theme of the show in 2003, was the "Minerals
of the Andes." Several private collectors and museums took part in the show,
who exhibited a wonderful selection of specimens of Andes origin, as well as
from other sources.
The show was a spectacular success, with the array of exhibits displayed
said to be one of the best ever. About two dozen museums took part in the
show, and brought out their best exhibits. The Star attraction among the
exhibits displayed by the National Museum of Natural History of the Smithsonian
Institution, was the 858-carat "Gachala Emerald," of Andean origin, which
was exhibited together with the famous Marjorie Merriweather Post emerald
necklace, whose 24 baroque polished round emeralds are also of Colombian
origin. Among the other mineral specimens of Andean origin exhibited by the
Smithsonian Institution, included two proustites, a Bolivian phosphophyllite
crystal accompanied by a faceted gem of 26.9 carats, and other rare
specimens like franckeite, andorite, helvite, and canfieldite.
Among the private collectors who displayed notable exhibits that received
much attention were Michael Scott, Gene and Roz Meieran, Bill Larson, Rock
Currier, Steve and Clara Smale and W. R. Danner.
Related :-
1) The Moghul Emerald
2)
The Duke of Devonshire Emerald
3)
Patricia Emerald
Please submit
your contributions ,comments and questions (See below)
-When you submit a question/comment we will build a
page exclusively for you. You can add more contributions, or let visitors
add comments and ratings
-The idea is Ask one or Answer one!
This way, you save yourself and others the trouble of asking the same
questions I'd appreciate a
little help here! Absolutely!!!
References
1.Gem by Gem -Beryls - Website of International Colored
Gemstone Association.
2.The Green Fire of Emeralds,
The Gemstone Forecaster Vol. 14 No. 1 - Part One
3.Gem by
Gem - Emerald - Website of International Colored Gemstone Association.
4.Harry
Winston - Wikipedia, the free encyclopedia.
5.Show highlights of the 49th TGMS Show - Mineralogical Record 2004
6.The
Emerald Deposits of Muzo, Colombia - Joseph E. Pogue, Transactions of the
American Institute of Mining Engineers, Vol LV, 1917.
7.Emerald - A
Cyclosilicate - Edna B. Anthony, the New Mexico Facetor.
8.GEO
347K GEM NOTES, Beryl - Website of the Department of Geological Sciences,
University of Texas, Austin.
