Lets Talk Gemstones

By Edna B. Anthony, Gemologist

(Contact the author for permission to reproduce this article in any form.)



The discovery of a vanadium-colored beryl exhibiting the distinctive chrome-imparted green of emerald added to the historical intrigue and to the controversy that has surrounded this queen of gems for centuries. Most members of our industry accept and market this material as emerald. However, Dr. Joel Arem in his Color Encyclopedia of Gemstones disputes this claim. His position is that the identity of a gemstone should not be determined by color but by its chemical composition. For the purposes of this article, we will recognize the difference but will make no distinction between the two.

For anyone seriously interested in learning about emeralds, a study of the lyrical essay and pictures presented by Dr. Eduard J. Gubelin in his Internal World of Gemstones (3rd edition, 1983, ABC Edition Zurich) is essential. He explains with classic simplicity the two entirely different geo-chemical processes that form emeralds in nature. These processes determine the myriad inclusions that make up the lovely "gardens" so prevalent in emerald interiors. The nature of these inclusions often provide diagnostic clues to the source of individual emerald gemstones.

Natural emeralds formed in pegmatites and in the surrounding metamorphic rocks contain solid, often eroded, mineral particles of the host rock called protogenetic inclusions. Rising acidic beryllium-bearing magmatic materials invaded the chrome-bearing iron-calcium and magnesium-rich rock outcrops, composed of mica schists and hornblendes of tremolite, actinolite, and related minerals. New minerals, including beryl, formed through pneumatolytic chemical reactions influenced by extreme heat and pressures. The temperatures and pressures involved precluded the participation of substantive amounts of any liquid water that may have been present. Therefore, the inclusions in these crystals seldom exhibit liquid inclusion characteristics common to those developed by hydrothermal processes. Exceptions noted are the crystals of Santa Terezinha de Goias in Brazil and those of the Swat Valley in Pakistan. Hydrothermal processes did influence the contact-metamorphic development of these deposits.

Known deposits of hydrothermally-created natural emerald occurred in connection with tectonic faults only in the Andes in South America, chiefly in Columbia. Hydrothermal solutions bearing albite rose into the hollow spaces in the carbonaceous clay slates of the Chivor region. Crevices in similar formations in the Muzo area filled with solutions containing calcite. These liquid solutions, saturated with mineral nutrients, sodium, chlorine, and fluid carbonic acid under high pressure, produced crystals that housed inclusions of a nature quite different from crystals formed from contact-metamorphic origin. Any solid mineral inclusions usually developed syngenetically with the emerald crystals from the solutions as the emerald crystal grew. Tiny halite (salt) and calcite crystals floating in myriad characteristic liquid cavities are the most common.

Other included minerals may be specific to a particular deposit of emerald. Dr. Gubelin makes the point that as new deposits of emerald are found, each presents its unique inclusion picture or signature. Since such features are "location specific" and other physical and optical properties of emerald vary, it seems logical to present characteristic information and data in arrangements according to the source and the crystal genesis.

There are reports that Babylonians were marketing emeralds as early as 4000 B.C. Pliny's mention that Nero used a cut emerald for a monocle was probably incorrect. Aquamarine or green beryl was more apt to have been the material utilized. It is unlikely that the ancient emerald mines in Egypt produced crystals of sufficient size and clarity needed for such an instrument. The two Egyptian deposits are situated south of Koseir in micaceous shists and gneisses in the mountain range west of the Red Sea. The evidence indicates that these were worked by the Egyptians as early as 1650 B.C.

Greek miners labored there for Alexander the Great. During Cleopatra's reign, some of the gems were engraved with her portrait and presented as gifts to her elite guests. The discovery of emeralds among the Roman ruins of Pompeii and Herculaneum before 1566 B.C. disprove the belief that emeralds were introduced into Europe from South America. In the early nineteenth century, the French scientist-adventurer, Cailliaud, rediscovered the abandoned Egyptian mines. With permission from Mehemet Ali Pasha, these mines were reopened using miners from Albania. As many as four hundred mineworkers toiled among the well-preserved timbers supporting the underground digs before they were again abandoned.

Baskets of materials ready for transport to the surface support evidence of an unexplained hasty departure. Mining now takes place only sporadically. The quality and transparency of the material are poor and no match to that found elsewhere in the world. In Precious Stones, Volume 2, Max Bauer attributes the good color of the Egyptian emeralds to chromic oxide. We have no definite data to provide reliable information about gems from this ancient source. It must be remembered that many green stones were designated as emeralds until science and technology evolved to determine the identification of specific minerals.

Farther south on the African continent, emeralds lie in six locations in Zimbabwe inside granitic pegmatites, serpentines, schists, and micaceous aggregates. Dr. Arem notes that color zoning, negative crystals, and two- and three-phase inclusions occur in addition to the solid mineral crystals prevalent in material of contact-metamorphic origin. The crystals found in the Shamva and Bubera Provinces are not suitable for gems. Gemmy crystals found in Filabusi Province show variations of the refractive indices of 1.587 to 1.594 for the ordinary ray with 1.583 to 1.588 for the extraordinary ray and a birefringence of 0.004. A specific gravity figure for them could not be confirmed.

The density of material from Belingwe Province is also a question mark; but Dr. Arem lists an ordinary ray index of 1.593-1.594 with 1.586-1.588 for the extraordinary ray. Birefringence is shown as 0.005 to 0.007. Characteristic inclusions are slender curving tremolite needles that traverse the interiors like dropped "pick-up-sticks." In Victoria Province, the alexandrite that accompanies this material has a specific gravity of 2.67 to 2.74. The refractive index of the ordinary ray varies from 1.576 to 1.591, the extraordinary ray from 1.572 to 1.585, with a birefringence of 0.004 to 0.007.

A British company, Rio Tinto, manages the modern and profitable operation that extracts the material from Sandawana's underground mines. The majority of its production consists of small, clean, deep green crystals. These are of a greater density (2.74-2.75), and they house inclusions that allow gems from this area to be easily recognized by experienced gemologists. Transparent muscovite flakes, pyrrhotite, hematite, and feldspar crystals are among the protogenetic mineral inclusions displayed. Bold "brushstrokes" enclosed by feathery cracks indicate stress from great pressures. Garnets surrounded by haloes colored yellow by weathered ilminite are sometimes nestled in a tangle of delicate curved tremolite fibres. These signature inclusions are a hallmark of the emerald crystals from this source. Refractivity shows o=1.590-1.596 and e=1.583-1.588, with a birefringence variation of 0.004 - 0.006 as the norm for the Sandawana material.

The emerald deposits in Zambia are of contact-metamorphic origin. After enlisting the aid of outside interests to develop its mines and establish gemcutting operations, the Zambian government nationalized the mines and the cutting operations in a seemingly unsuccessful attempt to control the industry. A great proportion of Zambian production is smuggled into Europe and finds its way to cutting centers in Israel. In his book, Emeralds, Fred Ward, G.G. mentions a government mine, Kagem, in northern Zambia where its production is sent directly to cutters in Israel. Dr. Arem also lists four mine sites in production.

The large and unusually clean, vanadium-bearing crystals from Zambia rival the quality of the chrome-colored material produced in the Columbian mines. Because of a hint of grey, probably caused by vanadium, the very high prices listed for the Zambian material are a bit below those commanded by the best Columbian gems. Distinct color-zoning and unusual blue tones that cause blue-green/yellow-green pleochroism are often found in this material. Some crystals exhibit a resemblance to "watermelon" tourmaline, exhibiting very light cores and a "rind" of dark green. Kafubu produces crystals of relatively high (2.77) density and refractivity.

Readings of 1.602 for the ordinary ray, 1.592 for the extraordinary ray, and a birefringence of 0.010 are not usual for gem emerald. Very small protogenetic crystals of magnetite in cloud-like arrangements frequently stain the surrounding areas in this material. Characteristic randomly distributed slender tubes filled with yellow limonite may have once contained other minerals. A wealth of minerals from the schists of Kitwe provides protogenetic crystal inclusions that inhabit gems from this region. Small clusters of orthorhombic chrysoberyl prisms are the most unusual, but various arrangements of tiny crystals of dark biotite are numerous. Muscovite-mica is common, and intergrown hematite platelets are often found. Apatite, dravite, and quartz crystals also appear in their interiors.

According to Dr. Gubelin and J. I. Koivula in the PhotoAtlas of Inclusions in Gemstones, the presence of rutile prisms pinpoints Kitwe as the source. Dr. Arem lists rutile as an inclusion in the emeralds of Habachtal; perhaps it occurs only in needle-form there. A specific gravity of 2.79 puts the Kitwe material in the upper range. Refractive indices of o=1.586 and e=1.580 and a birefringence of 0.006 vary little.

The deposits of emerald in the amphibolite schists of Miku feature inclusions of the serpentine mineral chrysotile, which are optically indistinguishable from tremolite and from the fine delicate fibres of the asbestos mineral, amianthus. Crystals exhibit a mid-range density of 2.74. The o=1.589-1.590 and e=1.581-1.582 rays of refraction are slightly above the norm. The birefringence can vary from 0.007 to 0.009. Dr. Arem refers to other deposits of emerald at Mufulira. For these, he lists a specific gravity of 2.68 with refractive indices of o=1.588 and e=1.581 and a resulting in birefringence of 0.007. It may be presumed that these crystals are of contact-metamorphic origin, but other data is lacking.

The Republic of Ghana in West Africa produces emerald of poor quality. Dr. Arem notes the density (2.70) and refractive data of o=1.589 and e=1.582, with a birefringence of 0.007. Information concerning the formation and the inclusions were not to be found in other references.

Alexandrite is a companion of the emeralds found in the biotite-mica schists and pegmatites of the Lake Manyara region of Tanzania. The usual biotite and mica inclusions, and crystals of actinolite, quartz and orthoclase may accompany growth tubes and square voids found in the Tanzanian material. Two- and three-phase inclusions also appear in material from this region. The o=1.585 ray of refractivity is stable, but the e=1.578-1.580 ray varies a bit. Birefringence can vary from 0.005 to 0.006. The specific gravity of 2.72 to 2.73 is in the mid-level range.

Across the continent in East Africa, deposits of emerald from Morrua in the Republic of Mozambique contain the expected protogenetic crystals of biotite, along with some in an unexpected helical form. Two-phase primary-growth voids of varying lengths sometimes appear parallel to the crystal axis. The density of material from this source is 2.73, with readings of o=1.593 and e=1.585 on the refractometer. A reading of 0.008 is the birefringence.

South Africa is the home of the Cobra Mine near Gravelotte in Transvaal. Eroded flakes of mica and feathery internal fractures commonly occurs in the crystals created by the metamorphic-pneumatolytic alteration of the schists of this region. Three-phase inclusions sometimes join the internal displays. The Cobra Mine material is unique in that it sports the world's only known occurrence of molybdenite crystals in emerald. Their curvy silvery presence eliminates all other sites as the origin of the gems that house these guests among their internal splendors. An upper range specific gravity of 2.75-2.76 accompanies refractive indices reflecting the norm: o=1.593-1.594 and e=1.583-1.586, with a birefringence variation of 0.006-0.007. According to Jaroslav Bauer and Vladimir Bouska in A Guide in Color to Precious and Semi-Precious Stones, emerald crystals measuring eight centimeters in length have been found in this area. It is here, too, that one crystal purported to weigh 11,000 carats was discovered on October 10, 1956. However, its whereabouts remain a mystery to this day.

On the island of Madagascar (Malagasy Republic), just off the east coast of Africa in the Indian Ocean, we again encounter mica schists as the home of emerald deposits. Dr. Arem notes that "more than fifty specific localities" produce "fine blue gem material". The Ankadilalana mine provides a frequently color-zoned material that encloses two-phase inclusions with a host of other mineral crystals. Apatite, biotite, goethite, hematite, ilminite, quartz, and tourmaline crystals all make an appearance. Both the density (2.73) and the variable refractive readings are in the upper ranges with a stable birefringence of 0.007, where o= 1.589 -1.591 and e= 1.581 -1.585 as the usual limits.

The emerald deposits from Austria in the Habach Valley of the Salzburg Alps are located in biotite schists almost identical to the formations in the Sandawana region in Africa. The variety of inclusions are also similar, but striking differences exist. Garnets are not present in Habachtal crystals. The tremolite fibres inclusions are always straight and can either be acicular, short and broad, or sometimes almost shingle-like. The tremolite, flakes of mica, and actinolite are the most prevalent of the mineral inclusions. They are often accompanied by apatite, biotite, epidote, rutile, tourmaline, and sphene. As in the Sandawana material, evidence indicating great pressure that caused partially-healed cracks is present.

The unusual feature here is that the healing fluid exhibits a deficiency of color-imparting chrome, and the healed fractures are often without color. Dr. Arem lists two sets of density and refractive indices. In the first, o=1.591 and e=1.584, with birefringence of 0.007, and specific gravity of 2.74. A second shows o=1.582 and e= 1.576, with a birefringence of 0.006, and density of 2.73. No explanation for these differences is given.

The reports by ancient historians of emeralds from "Scythian lands" may have referred to crystals from the Urals, but these claims cannot be substantiated. It was much later that emeralds embedded in interfoliated micaceous and chlorite schists and gneisses near Sverdlovsk (formerly Ekaterinburg) were found. These are companions of the alexandrite chrysoberyl and of the phenakite crystals found there. A peasant reputedly discovered this site on the bank of the Takovaya River. He noticed several green stones in the debris at the base of a tree uprooted by the wind during a violent storm. This became the source of emeralds for the Czars and the elite of Russia and Europe for many years. The finest emeralds from this site are the glory of the Russian crown jewels and rival those found in South America, but most are of lesser quality. The origin of a single and large, very fine, transparent crystal that was found in the gold sands of the Shemeika Valley in the Ekaterinburg district remains a mystery.

Inclusions in the material from the Urals include the expected biotite-mica, seldom found tourmaline crystals, and a form of actinolite unique to the region. Cleavage cracks transverse the nearly transparent actinolite rods at intervals and create the appearance of bamboo canes strewn throughout the interior. The refractivity of Ural emeralds varies little with readings of o=1.588 and e=1.581, with a birefringence of 0.006 to 0.007. The specific gravity reading of 2.74 is unremarkable.

Deposits of emeralds formed by metamorphic processes have been found in granite at Eidsvoll, Norway. These have had no great impact on the supply of gemstones. The Norwegian material exhibits a density of o=1.590-1.591 and e=1.583- 1.584, with a birefringence of 0.007. Density varies from 2.68 to 2.70. Interconnected growth tubes among moss-like inclusions cause a cloudiness in these stones.

In the United States, in a few areas on the east coast, and in the states of North Carolina and Connecticut, minuscule amounts of emerald crystals have been recovered. Only small emerald crystals in albite matrix have been found with hiddenite and the other gemstone varieties unearthed at Stony Point, North Carolina. An exception is a lovely 111 carat crystal recovered from privately owned land near Hiddenite. Material from these sources house quartz crystal inclusions. Fluorescence is exhibited in long-wave ultraviolet light. Refractive readings of o=1.588 and e=1.581, with a birefringence of 0.007, and a specific gravity of 2.73 reflect the norms for American emerald.

Two sites in southwestern Australia produce the emeralds of contact-metamorphic origin on that island continent. The schists of Poona yield material with densities of 2.69-2.70 and refractive indices of o=1.578- 1.579 and e=1.572, with 0.005 to 0.007 birefringence. Pegmatitic material at Emmaville has lower indices of o=1.575 and e=1.570, with the birefringence stable at 0.005. A lower specific gravity (2.68) is also present. Dr. Arem notes some three-phase inclusions present, with biotite appearing profuse among tubes and "daggers". It is indefinite that the presence of fluorite crystals is exclusive to the material from this source.

In his book, Emeralds, Fred Ward, G.G. explores the relationship between India's turbulent history and its fabulous treasures, including emeralds amassed by the ruling maharajas and other powerful families. He believes that, although emeralds had been imported from Cleopatra's mine for thousands of years, the exquisite gems of the Indian collections came from the Muzo mine in Columbia, South America. After Spain conquered Peru and then seized the deposits at Muzo, the emeralds were transported from Spain, and later shipped from the Philippines, to this lucrative market in Asia. Contrary to local belief and to the lore of "Old Mines", it seems there is no explicit documentation to explain any existence of emerald deposits in India, Pakistan, Afghanistan, or the Urals. No evidence exists that would prove the origins of these gems, as the deposits at Ajmere-Merwara in India were only discovered in 1940. It is unclear whether hydrothermal conditions influenced those deposits.

In the Internal World of Gemstones, Dr. Gubelin states that Indian emeralds are "rich in liquid inclusions" that accompany the protogenetic minerals. Dr. Arem mentions two-phase inclusions and gas bubbles present in prismatic voids parallel to the crystal axis. Other references are silent on this point. Apatite, chloroapatite, and biotite crystals also appear, and semi-transparent elongated diamond-shaped mica flakes are often common. Fuchsite mica provides one of the diagnostic inclusions for Indian emeralds. The appearance of twinned negative crystals of uneven widths and lengths offers another clue. These usually develop on one side of a mica leaf and resemble a stylized comma. Material from Ajmere-Merwara exhibits mid-range refractive readings of o=1.595 and e=1.585. Birefringence readings can vary from 0.007 to 0.010. A specific gravity of 2.74 also reflects the norm.

Miners of Afghanistan endure incredible hardships to recover the emeralds from the Panjsher Valley deposits, discovered in 1970. Workers are plagued by a high altitude, a harsh climate, and terrible civil unrest. They then face the dangers of transporting the scant production on foot through the Kyber Pass to the market in Peshawar, Pakistan. References make no mention of the quality, formation, chemical composition, inclusions, or physical and optical properties of these hard-won gems. A few years ago, Paul Hlava examined a couple of dark green Afghanistan emerald crystals using the SEM, and he confirmed the presence of both vanadium and chromium in the crystals.

The production of emeralds from deposits in the Himalaya mountains in Pakistan, discovered in 1960, is closely controlled by the government. Again, extremely harsh climate conditions prevent the exploitation of known sources at the higher altitudes. At lower elevations, hydrothermal conditions influenced the depositions in the contact-metamorphic formations of the Swat Valley. Curving arrays of secondary fluid inclusions in basal plane cleavages of the enveloping crystals mark the gems as natives of this region. Only a footpath beside the Kotkai River, winding its way through the narrow rugged valley, leads to the spectacular setting for the Gujar Kili mine. Severe weather conditions restrict operations during winter. The hand-dug output here is very limited.

Near Bucha, ultra-mafic material surrounds the veins of the talc-quartz-carbonate precipitate where the emeralds are extracted. These exhibit high refractive indices, as o=1.60 and e=1.590, with a birefringence of 0.010. In Mingora, characteristic crystallites of dolomite drift among the fluid inclusions in the gems recovered from dolomitic talc schists embedded in the mother-rock. Specific gravities for Swat Valley mine materials range from 2.75 to 2.78. The refractive indices vary from o=1.595-1.600 and e=1.588-1.593, with a birefringence of 0.007.

On the other side of the earth, Brazil, with its untold wealth of gem deposits, contributes more emeralds by volume than any other producer in the world. The outcome of a dispute involving renowned geologists, scientists, and members of the gem industry makes this possible. The controversy involving the question of whether to consider beryl colored by vanadium as emerald began in Brazil with gem discoveries in the 1960s. The question was resolved for most members of the jewelry industry by a report issued in 1963 from the Gemological Institute of America. It examined vanadium-colored gems from the Bahia region's Salininha mine and declared them to be "natural emeralds". The mine has since been flooded to make way for a hydro-electric project, but the impact of the decision regarding the material from its mica-schistic depths has changed the industry.

Almost all of the crystals recovered from Salininha exhibit an unusual small rod-like hexagonal form and show refractive indices of o=1.589 and e=1.583 and a birefringence of 0.006. Density measures 2.71. Three other producing mines are located in the Bahia area. Gems from these deposits harbor liquid films and two-phase inclusions, as well as talc, biotite, and dolomite crystals. The mica schists of Carnaiba may contain the most extensive emerald deposits in the world. Its material carries a specific gravity of 2.72, with refractive index readings of o=1.588 and e=1.583. Birefringence range is 0.006 to 0.007. Its sister mine of Brumado registers low refractive indices of o=1.579 and e=1.573, with a birefringence varying from 0.005 to 0.006. The density at 2.68 is the lowest listed by Dr. Arem for emeralds. On the other hand, crystals from Anage have the highest specific gravity shown with a 2.80 reading. Rays of refractivity measure o=1.584 and e=1.576, showing a high birefringence of 0.008. Pictures of biotite, chromite, and pyrite crystal inclusions in emeralds from Itabira can be found on page 246 of the PhotoAtlas of Inclusions in Gemstones by E.J.Gubelin and J.I. Koivula. Other information concerning this source and material could not be found in available references.

The Minas Gerais region of Brazil is known for its production of a profusion of gemstone varieties, including sources of emerald at various locations. Remarkably, the only data on emeralds from this region is provided by Dr. Arem. He specifies a density of 2.71 to 2.73 and refractive indices of o=1.578-1.581 and e=1.572-1.576, with a variable birefringence of 0.006-0.009. The bluish-green emeralds from Santa Terezinha de Goias, like the emeralds from Pakistan, are located in contact-metamorphic formations influenced by hydrothermal processes. The talc-biotite schists here contribute hematite, pyrite, and calcite crystals to the inclusion scene.

Characteristic to emeralds from this source are dolomite crystals accompanied by numerous chromite grains. Typical, too, are "paving stone" patterns formed by planes of thin liquid films. Specific gravity ranges from 2.70 to 2.76. Refractive indices vary from o=1.588- 1.593 to e=1.580-1.586.

Gemstone Properties
beryllium aluminum silicate
Be 3 Al 2 (Si 6 O 18 )+Cr,V
silicate; cyclosilicate
Crystal System:
hexagonal; per Schumann, trigonal
emerald (contact metamorphic pneumatolytic and hydrothermally influenced contact metamorphic origins)
unusual trapiche patterns; chatoyancy and asterism are rare
transparent, translucent, semi-translucent, and opaque
prismatic columnar
difficult for basal, brittle
conchoidal to uneven
Fracture Lustre:
vitreous to resinous
Specific Gravity
varies from 2.67 to 2.78
7.50 to 8.0
poor, a very delicate gem
Refractive Index
varies from o=1.575 to 1.602; varies from e= 1.570 to 1.592
varies from 0.005 to 0.010
Optic Character
uniaxial negative
varies and is distinct in strong colors
SW usually inert, at times weak yellow or green; LW rare weak red or orange
diagnostic; thin lines in red; weak lines in blue; broad band in violet; iron content in Zambian material causes spectrum characteristics of aquamarine
Color Filter
no information
Aqua Filter
no reaction 
Chelsea Filter
varies; weak to moderate red in Columbian material; (chrome) green in Zambian material; (vanadium)
affected only by hydrofluoric acid
Thermal Traits
avoid thermal shock; very fragile; remove stone during jewelry repairs; avoid ultrasonic cleaners
nearly all material oiled at mine sites; cedarwood oil; palm oil; Opticon; colored oils, waxes, and resins; recently patented Gematrat process
(see preceeding text)