Emeralds: Part One by Paul Hlava
Notes by Nancy L. Attaway
Paul Hlava spoke to the Guild on “Emeralds: Part One” and covered the mineralogy,
the geology, and the geography related to emeralds. Paul defined emeralds
as a variety of beryl noted for having a bright, intense, saturated green
color, caused by the presence of chromium (and/or vanadium) in the crystal
structure. Paul began his talk with a quick demonstration of how man-made
emerald crystals (Chatham) fluoresce red when hit with an ultraviolet light
in a darkened room, showing the presence of the chromium absorption spectrum.
Emerald is the birthstone for May.
First, Paul explained some of the physical properties of emeralds. Emeralds
have a hardness of 7.5 to 8 and are brittle due to the coloring agent. (More
on that later.) Emeralds show a vitreous lustre and have a density of 2.67
to 2.75. Emeralds have two cleavages: one, a basal pinacoid (poor), and the
other, a hexagonal prism (rarely seen). Emeralds fracture in a conchoidal
to an irregular manner and show a green/white color streak. Emeralds have
a refractive index of 1.566 to 1.591 and have a dispersion of 0.005 to 0.009.
Emeralds are uniaxial negative and pleochroic (yellow to green and blue to
green). The emerald spectrum is very diagnostic. The spectral wavelength shows
fine lines in the red, weak ones in the blue, and broad absorption in the
violet. Emeralds show a red color in the Chelsea filter.
Paul then explained the chemistry of emeralds. Emeralds contain Cr3+ and
V3+ (chromium and vanadium). Pure beryl is colorless; Be3Al2Si6O18. Beryl
may also contain water and alkalis (Li, Na, K, Rb, and Cs), and the alkalis
alone can exceed 8 weight percent. Beryl may contain: Mg, Ca, Sc, Cr, V, Mn,
Fe, Zr, Nb, Sn, and W. The color of emeralds is a result of impurities within
the beryl crystal. Modification of the color by the presence of other impurities
can cause the green color to vary from bluish green to yellowish green. Depth
of color is related to the amount of coloring metals present. Paul said that
to be an emerald, beryl must contain chromium levels greater than 0.002 weight
percent to greater than 2.00 weight percent.
Paul said that the chromium atoms go into the aluminum site of the atomic
structure of beryl. Chromium adds stress in the crystal structure, forming
“jardin”, because the chromium atoms are bigger than the spaces in the atomic
structure of beryl. The fact that emeralds contain both beryllium and chromium
is very interesting, in that beryllium and chromium are geochemically incompatible.
They do not like to occur together. Chromium came from the magma in the silica
“milk” first, and beryllium emerged from the magma last. Hence, chromium and
beryllium are concentrated at opposite ends of the crystallization sequence.
Emeralds are found where these two ends are mixed, a rare occurrence. Therefore,
emeralds are rare.
Paul stated that emeralds are always green. He said that the most intense
color of emerald is produced when they are cut with the table parallel to
the C axis. The rectangular “emerald cut” is the best faceting shape to maintain
carat retention, as it follows the crystal’s original shape. The largest gem
quality emerald found weighed 1,759 carats.
Paul showed a diagram of the emerald structure. Looking down the C axis,
emerald consists of hexagonal rings of silicon atoms, six-fold rings, each
surrounded by four oxygen atoms in tetrahedral arrangement. The rings are
stacked one over the other and connected by bonds between alternating aluminum
and beryllium atoms. Each aluminum atom is surrounded and bonded to six oxygen
atoms, and each beryllium atom is surrounded and bonded by four oxygen atoms.
A striking feature of this atomic arrangement is that the SiO rings are aligned
exactly over each other so that their openings form continuous channels parallel
to the C axis. Emeralds, as beryls, belong to the most complete class of symmetry
of the hexagonal system: holosymmetric, dihexagonal-bipyramidal.
In explaining the geology of emeralds, Paul stated that emeralds are found
in a fairly restricted set of metamorphic rocks, such as biotite-phlogopite
schists, carbonate schists, talc-chlorite schists, etc., that have been intruded
by beryl-bearing pegmatites. The Colombian deposits are in carbonaceous shales
and limestones that had been invaded by hydrothermal solutions. Most other
beryls are usually found in pegmatites. Emeralds have been found in all of
the continents, with the exception of Antarctica. However, they have been
found in only a few places on each continent. Most of the finest emeralds
come from alluvial deposits. Colombian emeralds are of consistently high quality
and serve as the benchmark of comparison for other emeralds.
Paul said that the most notable occurrences of emeralds were in South America,
primarily in Colombia and Brazil. In Colombia, near Boyaca, lies the famous
Muzo district, home of the Muzo mine and the Coscuez mine, as well as others.
Muzo is the world’s most famous and valuable emerald mine, setting the standard
for quality and color. Also in Colombia, near Chivor, lies the famed Chivor
mine and the Gachala mine, among others. In Brazil, near Bahia, lies the Salininha
mine, where the emeralds contain vanadium (V3+). The Brazilian government
flooded the Salininha mine for hydroelectric power. The Carnaiba mine, one
of the world’s largest emerald deposits, is nearby. Near Ceara in Brazil
are several mines, including the Goias mine and the Santa Teresinha de Goias
mine, where hundreds of unsupported tunnels run in the hillsides more than
three hundred feet deep. Brazil is the world’s largest volume emerald producer.
In Brazil’s famous Minas Gerais is the Nova Era district and the Capoeirana
mine. The Itabira district of Brazil contains the Belmont mine.
Other notable occurrences of emeralds are in Asia and in Africa. Emeralds
are found in Afghanistan’s Panjshir Valley district and in West Pakistan’s
Swat Valley district, the Gujar Kili mine; in the Mohmand district, the Mingora
and Bucha mines. The Afghans miners labor under the worst conditions anywhere
for mining emeralds. The emerald miners in Pakistan also work under very harsh
conditions. Emerald mining in both Afghanistan and Pakistan involves mining
in areas reached only by footpaths, where workers dig by hand in steep terrain
accessible for just a few months a year, due to the high altitude long winters.
In the Commonwealth of Independent States, emeralds are found in the Ural
Mountains and in the Sverdlovsk district. In India, the
Orissa district and Ajmer yield emeralds. In Africa, emeralds are found
in Zambia’s Kitwe district, the Miku mine, at Mufulira, and in the Kafubu
district, the Kamakanga mine. Emeralds are found in Zimbabwe’s Bikita district
at Sandawana (an underground mine), also Mberengwa and Victoria. The Rio
Tinto mine in Zimbabwe uses modern mining technology and security methods.
Zambia and Zimbabwe produce most of the emeralds in Africa. Emeralds are
also found in Egypt; in Madagascar’s Ankadilalana mine; in Mozambique at
Morrua; in Nigeria; in South Africa’s Cobra mine and in the Transvaal; in
Tanzania in Arusha and at Lake Manyara; and in Ghana.
Other occurrences include Australia, Western Australia’s Poona district;
and Austria at Habachtal. Eidsvoll in Norway has emeralds in granite. Poor
quality emeralds were found in New Mexico’s Black Range in the 1890’s. Emeralds
were found in North Carolina near Spruce Pine.
Recently, some very fine quality emeralds have been unearthed near Hiddenite,
North Carolina that rival the best quality emeralds from Colombia. An 88-carat
rough emerald crystal from this new mine was cut into two very fine gems,
an 18.88-carat pearshape named the Carolina Queen and a 7.85-carat oval named
the Carolina Prince. Another giant emerald crystal, the 858-carat Empress
Caroline, is one of the largest emeralds mined in North Carolina. Two other
significant emeralds from North Carolina are a 3.40-carat heartshape named
the Heart of Carolina and a 3.37-carat emerald cut gem named the Princess
Paul discussed the primitive mining methods used at most mine sites for
extracting emeralds. Emeralds are mostly unearthed from open pits, but several
underground mines exist. A few emerald mine sites have been described as
resembling coal mines. Barefoot miners use picks and shovels and wear no
safety equipment for head, eyes, ears, hands, feet, and lungs. Hundreds of
small (three meter square) claims exist on steep, muddy hillside slopes with
stick scaffolding, tarp covers, and little or no shoring. Consequently, many
cave-ins occur. Some of the more modern mines, such as the Muzo mine and
the Rio Tinto mine, use tractors and bulldozers, drilling equipment, and
some explosives. No paperwork is required for the majority of the small claims.
Miners simply rope off their area downstream from company claims, dig, and
sift. Paul said that disputes often erupt over claims, and many end in violence.
Nowhere is the search for emeralds more violent than in Colombia, and Muzo
is considered the most dangerous. Bandits lie in ambush for buyers, who come
into Muzo with cash and leave Muzo with emeralds. Armed patrols guarding emerald
buyers have even been attacked by well-armed bandits. The independent miners,
who work downhill from guarded company claims, also risk life and limb to
work their claims that lie in dangerous terrain. The danger lies from bandits,
from other miners who may contest their claim, and from the working environment
itself. Hence, murders are not uncommon. In Colombia and in many other parts
of the world, emerald miners endure some of the most dangerous and difficult
conditions imaginable to extract emeralds because the gems are so highly
Paul included many slides of marvelous emerald crystals and magnificent
emerald jewelry, along with slides of emerald mine locales in his very animated
talk. Paul also showed several pictures that illustrated the atomic structure
of emerald. Paul will continue in November with “Emeralds, Part 2”, which
will cover the history and lore, cutting, gem treatments, synthesis, and
noted inclusions. Don’t miss this talk.