The verdant beauty of the emerald has entranced mankind throughout the ages. It is particularly appropriate that this lovely green gem has been chosen as the birthstone for the month of May to symbolize the beauty and promise of nature in the spring of each year. It is equally appropriate that it has been chosen to symbolize faith, kindness and goodness. Long ago, emerald was dedicated to the goddess Venus, and lovers were told that it was endowed with the power of revealing the faithfulness of the beloved:
"It is a gem that hath the power to show
If plighted lovers keep their troth or no.
If faithful, it is like the leaves of spring
If unfaithful, like those leaves withering."
Emerald, the most valuable member of the beryl family and one of the most highly prized of all gems, is a chrome-rich aluminum-beryllium silicate. The name beryl (pronounced BARE-ill, not "burl") evolved from the Greek through the Latin "beryllus" the meaning of which is uncertain. Emerald is a derivative of an ancient Persian word, and has come to us through such corruptions of the Latin "smaragdus" as "esmeraude", "emeraude" and" esmeralde". The present spelling did not become a part of the English language until the sixteenth century.
The history of the emerald is embedded in a tangle matrix of legend and superstition information that is as fascinating as it is voluminous. It has often been said that no other gem in all the world possesses the glory of color of emerald. Unlike some precious stones, the value of a richly colored crystal is obvious to even the most ignorant savage stubbing his toe against it in the humid jungle. Ancient and primitive man told marvelous tales of this regal gem, whose beauty was a miracle to him. Pliny the Elder, that learned Roman scholar whose observations on the beauties and wonders of nature are so often quoted today, once gave this reverent appraisal of emerald in these words:
"Indeed, no stone has a color that is more delightful to the eye, for, whereas the sight fixes itself with avidity upon the green grass and the foliage of the trees, we have all the more pleasure in looking upon the emerald, there being no green in existence more intense than this. And then, besides, of all the precious stones, this is the only one that feeds the sight without satiating it. Neither sunshine, shade nor artificial light effects any change in its appearance; it has always a softened and graduated brilliancy."
The Romans also took a seriously medical view of emerald's pleasing qualities on the eye. Pliny further records:
"If the sight has been wearied or dimmed by intensively looking on any other object, it is refreshed and restored by gazing upon this stone. And lapidaries who cut and engrave fine gems know this well, for they have no better method of resting their eyes than by looking at the emerald, its soft, green color comforting and removing their weariness and lassitude."
It is also said that the emperor Nero was accustomed to "refresh and restore his vision" by viewing the heat and violence of the gladiatorial shows through the cool clarity of a fine emerald. Whether the gem was fashioned into a lens or merely used as a mirror (or whether it was actually a piece of green glass) is a moot point.
The first emerald mines of recorded history were those in upper Egypt, the famous "Cleopatra mines". The location of these mines became lost, probably during one of the many times that Egypt became overrun by conquerors from other lands. Their location was not rediscovered until 1818, when the Viceroy of Egypt sent a French scientist, Cailliaud, in search of them. It is believed that the stones that were so revered by the people of the later Roman civilization came from this source.
Although Roman scientific observation was often childlike, it was occasionally startling accurate. They recognized the basic truth about the emerald: that it is a member of the beryl family of gems. To quote Pliny: "Beryls are of the same nature as emeralds, or at least very similar". In contrast, they made the serious error of classifying most green stones as a variety of emerald. In all, they enjoyed twelve "varieties" of this popular gem. Among those miscast into the role of emerald were green sapphire, turquoise, smithsonite, malachite, jasper and even glass.
A surprising variety of virtues have been ascribed to the emerald, in addition to those just mentioned. It was supped by the ancients to give a supernatural ability to foretell future events. It was thought to strengthen the owner's memory and his eloquence and to quicken his intelligence, thus producing a higher degree of honesty. Emerald was believed to make the wearer more economical and therefore more likely to become wealthy. As a preventative against ills, the woman who wore an emerald was believed to be immune from epilepsy and other serious disorders.
Roman legends ascribed to this gem even more august powers than the merely medical. One of these legends, as recorded by Pliny, says:
"On the Island of Cyprus, near the tomb of Hermias, there was in ancient times a marble statue of a lion. In its head were set two fine emeralds as eyes, looking out to sea. They glittered so brightly, piercing deeply into the water, that all the tuna fish of the coast were frightened and fled from the nets and the other paraphernalia of the fishermen. For a time the fishermen were nonplussed, but, finally realize what had happened they put other eyes into the lion's head, removing the emeralds."
Whether the Romans took the story seriously is not known. They did, however, take seriously the theory that gems "ripened". In describing a stone that was half jasper and half emerald, Pliny referred to the jasper as gradually turning into emerald and considered the stone "unripe" or in an incomplete state of metamorphosis. This myth was a natural out growth of the age-old belief that precious stones actually lived, supported by the idea that tropical heat was essential for the full development of their beauty. In the seventeenth century, this belief appeared again in the writings of Thomas Nicols, an English lapidary, who quoted an ancient gemologist as follows:
"Every gem, saith he, hath a matrix formed out of some stone or other, in which matrix, by the distilling of certain nutritive juice, is nourished".
Half a world away, in South America, the same story cropped up. Garcillasso de Vega, a writer of that day, said "Emeralds take their tincture from the nature of the soil from whence they are produced, ripening there with time like fruit in their proper seasons". It was in South America that the world's finest emeralds were to be found. The mines in Colombia South America, have a history somewhat similar to those of Egypt. When the Spaniards conquered the Incas, they found many fine emeralds that had been produced in Colombia. At the point of the sword, the Incas surrendered the stones they were unable to hide. But this was not enough for the treasure hungry Spaniards. Rich already beyond their highest expectations, they were not rich enough they wanted to know the source of the emeralds. On this point, the Incas remained stubbornly silent, even under torture. So the plunderers set out to discover for themselves the source of the valuable stones. But the Indians had eliminated with such care all trace of the tunnel-like openings into the underground pockets of emeralds, and so quickly did the jungle growth conceal the paths that led to them, that the Spaniards did not succeed in finding a single mine. It was not until years later, in 1955, that one of the mines of Muzo, in Colombia, was discovered quite by accident. In the beginning, the Spanish Crown extracted a tribute of one-fifth of all mineral wealth obtained, including emeralds. Occasionally, however, special emerald mining concessions were granted to persons who found favor with the government.
The source of old Indian emeralds mine is not known but can be traced either in the mines near Udaipur or Kanta Banji in Orissa. The old Indian Emeralds were of the first quality.
One of the most interesting anecdotes regarding the early development of these mines described the operations of a titled Spaniard who had received as reward for services rendered an exclusive mining concession for one of the famous deposits. He expended practically his entire fortune without results, although outcrops on the property had indicated most attractive possibilities for the finding of rich pockets of emeralds. When his rights were about to terminate, and as a forlorn hope, he followed the suggestion of one of his laborers and dug into what had been supposed to be a worthless formation that had shown no surface indication of emerald producing veins. To his amazement, he uncovered a spectacular deposit, and within a few days extracted emeralds of a value exceeding his entire investment. He selected a large parcel of stones from the lot and sailed to England, where he expected to sell them to the lapidaries of London, Brussels and Amsterdam. He furnished and decorated a room in a London tavern and invited all of his prospective customers to a magnificent banquet, after which he exhibited his collection of emeralds on a large table, amid the most appropriate setting, confidently expecting to obtain immediate offers.
The gem dealers were astonished at the quantity and quality of the assortment. They asked, cautiously, whether any more emeralds were to be found at his mine. In an attempt to brag of his achievement, he accounced that all of the stones had been recovered with a few days of labor and that more remained unmined. The effect on the audience was immediate they visualized a large production of emeralds about to be thrown market and refused to make a bid. The seller attempted, in vain, to correct his falsifications. It is said that his emeralds remained unsold for nearly two years, during which time the purchasers had satisfied themselves that the gems offered were likely to be the only product from that particular locality.
Unlike many famous diamonds, emeralds have rarely been given individual names, despite the fact that a number have had fascinating historical backgrounds. The only name that is generally familiar is the Devonshire Emerald, a 1383.95 carat uncut Colombian crystal of fine green color. It was given to the sixth Duke of Devonshire by Dom Pedro the First, Emperor of Brazil, when he, came to Europe after his abdication in 1831. It is on permanent loan to the British, Museum of Natural History. The American Museum of Natural History, in New York City displays a 1200-carat crystal of fine color known as the Practical Emerald.
A number of unusual carved emeralds are in existence. One of these is a 2680 carat unguent jar that was cut in 1642 for the Hapsburg family. Another example is a large drinking cup, now in the American Museum of Natural History, that once belonged to the Emperor Jehangir. A 900 carat carving referred to as an "emerald mountain" was sold in New York City in the 1950's.
Probably the most famous single piece of emerald-set jewelry in the world is the Crown of the Andes, which includes the Atahullpa Emerald, a 45-carat stone named after the last Inca of Peru. Created in 1953 from a solid block of pure gold, it was made for the statue of the Madonna in the Cathedral of Popayan. During its long history, the crown was captured by the English in 1640, who held it for only three days; and again, in 1812, it became a prize of war during the revolution in which Simon Bolivar freed the South American colonies from Spanish domination. The Crown of the Andes contains 453 stones, weighing a total of 1521 carats. It is presently owned by a syndicate headed by a New York jewel dealer.
The blue to green aquamarine and other colors of beryl apparently were not as highly esteemed as emerald by the ancients, although beryl is mentioned in the Bible and early writers described gems that evidently belonged to the species. A notable biblical mention is that found in the Song of Solomon, where it is said:
"O daughters of Jerusalem, this is my beloved and this is my friend; his hands are as gold rings set with the beryl."
Alternating with bloodstone as the birthstone for March, aquamarine has long been considered the symbol of happiness and ever lasting youth. In the Middle Ages, it was supposed to give the wearer insight and foresight. It also was thought to induce sleep. If a person held an aquamarine in his mouth, it was said that he could call a devil from hell and receive answers to any questions he might ask. It had further powers over evil, since, when consecrated and worn, the wearer was conqueror over all wickedness. Water in which an aquamarine had been soaked was believed to cure eye troubles, stoppage of breath and hiccups. The name of the variety is derived from the Latin word meaning "sea water" an apt description of the color of many stones seen on the market.
Many aquamarines of huge size have been found. In 1910, for example a crystal was found in Brazil that weighed 243 pounds and was nineteen inches long and sixteen inches wide. It was a six-sided hexagonal prism with a flat top and base. The outside of the crystal was greenish and the inside was blue, and it was so transparent that objects could be seen through the long dimension. It was sold for $25,000 and cut into many high quality gems. The American Museum of Natural History owns a 13 pound uncut piece of the green outside portion of this tremendous crystal. Since 1946, the Manufacturers Trust Co. of New York City, has held a 56 pound aquamarine crystal pending settlement of litigation regarding its legal ownership.
The British Museum of National History boasts a flawless, sea-green, step-out aquamarine that weighs 879.5 carats. The American Museum of Natural History has a number of notable cut specimens, including a 271 carat Russian stone, a 355 carat Ceylon stone, a Brazilian emerald-cut stone weighing 144.51 carats, and a top quality stone of 400 carats. What has often been said to be the most beautiful aquamarine ever discovered came from Brazil and was once owned by the emperor of that country, Dom Pedro. Another notable specimen from Brazil was presented by that government to Mrs. Franklin D. Roosevelt in 1935; it weighs 1847 carats and is presently in the Hyde Park Museum, New York.
Morganite, the light purple-red to purplish-red beryl, was named after J. Pierpont Morgan, the famous financier, in recognition of his contribution to mineralogy and gemology in presenting his unrivaled gem collection to the American Museum of Natural History. This collection includes some of the finest morganites known. One is a 58.79 carat, heart shaped stone from Madagascar; another is a six inch Chinese carving, which according to Museum authorities, is undoubtedly the finest carved morganite in existence.
Among the varieties of the mineral beryl are included some of the most important gemstones. Emerald and aquamarine are both prominent in the world of gems and golden beryl and morganite provide exceptionally attractive stones that are potentially important. Emerald is certainly one of the most valuable gems one that has always been included in lists of the few "precious stones".
Medium light to medium dark tones of green beryl are called emerald. Stones that are light or very light green are properly called green beryl rather than emerald. Since it has been used for many years, the usual trade classification based on geographical location is given below for information, but with the recommendation that the grading system on the price chart later in the assignment replaces the locality terminology.
The finest emeralds have always come from this South American republic. Relatively clear pure green, slightly yellowish or slightly bluish-green stones are called Colombian emeralds. Actually, the average output from the Muzo, Chivor, Cosquez arid Gachala mines differs and each, produces a range of qualities. A fine emerald may be referred to as Colombian, regardless of source, or it may be called a Muzo, Chivor etc. Muzo produces the finest colors, but the stones are usually more heavily flawed than those from Chivor.
Russian, or Siberian Emeralds
The emeralds produced by the mines of the Ural Mountain area are characteristically more yellowish green, more heavily flawed, and slightly lighter in color than Colombian stones.
Most of the green material produced in Brazil is more properly classified as green beryl, but some stones are sufficiently deep in tone to be called emerald. This pegmatite material is usually almost free from flaws. Heavily flawed crystals are found in micaschist in Brazil, but they are not ordinarily designated Brazilian emeralds in the trade.
These emeralds found in a schist bordering a pegmatite in the Belingwe Native Reserve country of Rhodesia are marketed under the name Sandawana emeralds. The color of this best quality material is a fine deep emerald green, but owing to the flawed nature of the crystals, cut stones over a quarter of a carat in weight are rare.
The term aquamarine is applied accurately to blue to greenish blue to bluish-green beryl; most commonly. the color is greenish blue. The tone varies from very light to medium dark.
Stones from Madagascar are frequently a medium dark blue, compared to the usual color, and any aquamarine that has this color is referred to as a "Madagascar."
Bluish-green stones are usually referred to as Brazilian aquamarines. (Note: This is also a misleading name that has been used for similarly colored topazs)
Beryl with a brownish-yellow color, sometimes referred to as "ginger brown" is called golden beryl. Stones in the yellow to brown color range are sometimes referred to as heliodor (HE-Iee-oh-door) by mineralogists, a name that is derived from two Greek words meaning "sun" and "gift".
Light purple-red to light purplish-red beryl is called morganite. Sometimes, light orange-red stones are also included under this term.
Other Transparent Varieties
Beryl also occurs in other colors, such as greenish yellow, orange and colorless. The colorless variety, which is rarely used for gem purposes, because it is too low in R.I. and dispersion to have much "life" is sometimes called goshenite (GO-shen-ite). The name is derived from Goshen, massachusetts, where it has been found. The greenish-yellow material is often called chrysolite aquamarine, because it resembles the variety of peridot with that color. The rich, medium tone of orange has never been given a separate name. Although it is rarely encountered, it is a very interesting stone in appearance no other gemstone has a color that resembles an orange beryl. Red beryl of medium tone was discovered in Utah in 1970, but too little transparent material was found to make mining pay.
Chatoyancy sometimes occurs in semitransparent beryl of various colors. Although some of this material is cut into cabochons to bring out the cat's-eye effect. It is usually too weak to be of any major importance as a competitor to chrysoberyl cat's-eye. It is particularly likely to occur in aquamarine and morganite, although a 7 carat cat's eye emerald in the Smithsonian Institution has merit. The Smith sonian also has a handsome orange beryl cat's-eye.
On occasion, dark yellow-brown to black beryl with a rather poor star is seen. It is sometimes confused with black star sapphire, but it is not very commonly used for gem purposes.
Interestingly enough, emerald and various other varieties of beryl seldom occur in the same kinds of deposits, although their manner of formation is similar. With the exception of emerald, all of the varieties tend to be associated with pegmatite dikes as the most important single source for these various colors. Emerald, on the other hand is found either in schistose rocks or as one of a number of minerals filling veins in other rocks; however, the mineralizing solutions or gases were magmatic in origin and therefore like pegmatites.
Emeralds in the important Colombian mines at Muzo occur in calcite veins that traverse both a sooty shale and a rather thin bedded carboniferous black lime stone. Despite their presence in a bedded sedimentary rock, the origin of the solutions that deposited the emerald crystals and calcite in the veins was pegmatitic in origin.
Below the formation in which the emeralds are found is a rock composed largely of albite feldspar. The rock which became albitized by the introduction of solutions from some deeply buried magma, is formed by a type of metamorphism that takes place at rather greater distances from the molten rock than would justify the usual term "contact metamorphism". Investigators of the area have remarked on the nature of the albite and its somewhat transparent nature and drusy concentration at places in the rock. It appears that the albite replaced the calcite in the formation. An adjoining rock contains large calcite rhombs. Undoubtedly, the solutions dissolved calcite from the rocks and re-deposited it in the veins. Also present are such evidences of the nature of the mineralizing solutions as fluorite and apatite.
In Russia, at Habachtal in the Austrian Alps, is South Africa, in Rhodesia, and in one Brazilian area the emeralds are found as a constituent of mica-schists. Emerald is one of the few gems that is not found in quantity in alluvial deposits; it is almost the only important gemstone that is mined exclusively from primary sources, the rock in which it occurs. The green beryl found in Brazil is a constituent in a dolomitic marble of the contact-metamorphic type. Although most gem occurrences of beryls other than emerald are in pegmatite dikes, they also occur in other kinds of deposits.
On occasion, aquamarine is found in mica-and talc schists and quartz veins. In Russia, it has been found associated with topaz and amethyst in a topaz-quartz rock cutting across granite. Most of the gem material, however, is found in pegmatite dikes and in most of the gem bearing pegmatites of the world. Beryl is much like topaz and tourmaline, in that it forms either as a vein mineral or in pegmatite dikes rather late in the cooling of a molten mass when the volatile constituents have become concentrated by the crystallization of the other ingredients. They may then be concentrated in dikes or pass out through fractures in the rocks, forming veins.
Since in its pure form beryl is colorless, the different varieties are colored by the presence of minute amounts of metallic oxides, other than those that are essential constituents of the mineral. When chromium oxide is present, the usual result is emerald, whereas aquamarine is thought to have been colored by ferrous iron, morganite by lithium and golden beryl by ferric iron.
Despite the fact that emeralds, are exceedingly rare in gem quality, crystals have been found in a number of localities throughout the world. The historical Egyptian mines, referred to earlier, have been worked only sporadically since their rediscovery, for the output consists primarily of pale-green stones containing many fractures and inclusions. By today's standards, the stones are suitable primarily for carving or for inexpensive cabochon-cut stones. In the early days, the mining was done by very primitive methods; however, from the condition of the mines when they were relocated, it was clear that they had been worked extensively, because the workings extend to a depth of more than eight hundred feet. The mines are located in northern Egypt, about fifteen miles to the north of Aswan. There are two localities, about ten miles apart, in a range of mountains that extends for some distance parallel to the west coast of the Red Sea.
By far the most important emerald localities today are those in the South American Republic of Colombia. Here, four groups of mines produce sporadically the bulk of today's solitaire size gem emeralds. The Muzo mines, discussed previously, produce the fines material, as they have throughout their history. Mining operations are carried out intermittently by the Colombian Government by open pit methods. Water stored in reservoirs is washed over the workings periodically to clean away debris and re-expose the veins of white calcite in the dark shale and limestone. It is in the calcite veins that the emerald crystals are found. The output is held at the Bank of Colombia and released to the market only as demand requires. When the supply is exhausted, operations are resumed. Between times "poachers" work the property on a clandestine basis, and a certain number of stones reach the market in this manner. The Muzo mines are near the village of the same name, about seventy-five miles to the north of Bogota, the capital of Colombia.
The Chivor mine, which was re-discovered in 1896, has been worked by private organizations. Ownership has changed a number of times in recent years, but the property has been worked fairly steadily. At the present time, the most recent company is in bankruptcy and the mine is being worked under a permanent receiver. It lies near the village of northeast of Bogota. The government owned Coseuez mine, situated approximately ten miles northeast of Muzo, has not been worked for a number of years.
The Colombian emerald mines are restricted to just a few areas of the Cordillera of the Andes Mountains in the Department of Boyaca and Cundinamarca, and are situated on the western side of this great range. The Muzo region is in the basin of the Minero River, and the Chivor district is in the Tenza Valley. According to the geological studies that have been made of the area, the emerald, bearing strata are confined to the Villeta formation of Lower Cretaceous age.
It is interesting to note that the emerald deposition may have occurred at approximately the same time as the emplacement of of the diamond pipe in Africa, since the rocks that the emerald veins traverse are not very many million years older than the diamond pipes, and the mountain building activity of the Andes must have been underway near the end of the Cretaceous Period, when the diamond pipes were formed. The emerald bearing veins are in a formation that lies on steeply uptilted rocks similar to the veins themselves. They are separated by a fault that was the probable path of the solutions and gasses from which the crystallization took place.
There is some mineralization in the rocks below the fault. It seems likely that the solutions followed the fault and that the gaseous portions thereof affected only the rocks above the fault, whereas the non economically mineralized liquid portions permeated the rocks below the fault. Just above the fault is a zone of strong, change to albite, and above this, in the old carbonaceous shale and limestone, are the calcite - and emerald bearing veins.
In contrast to the open-pit mining at Muzo, where the very steep hillsides are terraced, the Chivor mine is now worked by cutting drifts into the hillside. Ore of the reasons for this is that they are considerably easier to lock and guard at night. When a pocket is opened late in the day at Muzo, it is sealed with clay and the foreman and mine manager put their signatures in the wet clay to make sure that the miners do not tamper with the cavity. "High grading" is a serious problem in the mines. At Chivor, this is avoided by preventing access to the mine tunnel. Pyrite is found in most of the veins and in Chivor emeralds, but it is absent in Muzo and Cosquez stones. Crystals found in a pocket are usually covered with iron stains and anything other than well-shaped crystals must be scraped to be recognized. The presence of a pocket or a series of pockets is usually heralded by the discovery of what the miners refer to as "morally", the word they use for very low-quality massive beryl. Well-formed crystals are called "canutillos".
The Gachala mine, which was discovered about 1956, is located in the Department of Cundinamarca, about five miles from Chivor. Purportedly, it was discovered by a local farmer who was leading his mule down a steep mountain trail when the animal tripped over a boulder and exposed a rough emerald. It is reached only after a number of hours on horseback from the town of Gachala. Stones are taken from boulders that were evidently displaced from higher on the mountainside. Apparently, the new discovery is too recent to have been worked out or to have led the miners to search out the original formation. The rock would seem to be the same as that at Chivor. It is the same geological formation as that in which the emerald bearing veins occur.
The government has taken over the mine, so presumably it will be worked on a comparable basis to the Muzo mine. Early reports indicate that the emeralds are of fine quality, but perhaps lightly too bluish. They are said to be nearly the equal of the Muzo output and of better color than the usual Chivor production.
Another historic source of emeralds was on the eastern side of the Ural Mountains, about fifty miles east of Sverdlovsk. In this region, a mica-schist contained topaz and tourmaline, as well as chrysoberyl and other beryllium minerals. Sverdlovsk was formerly called Ekaterinburg, which was to pre Soviet Russia what Idar-Oberstein is to Germany today. The principal industries of the area were mining and cutting gemstones. In general, the Russian material was much more heavily flawed than that from South America. Also, the color of large crystals was inferior to that of the South American stones, although the smaller stones were more strongly colored and therefore satisfactory for calibre. Today, Sverdlovsk is a metropolis with a population in excess of 500,000 and is still a major mining center, probably for lithium, beryllium, columbium, tantalum and other pegmatite metal sources. It is possible that emeralds and other gemstones are being produced even now; if so, however, they are not affecting the market. Many of the Russian emeralds known to be reaching the trade are those from estate pieces, but recently it has been reported that it is possible to purchase freshly mined stones in Moscow.
Emeralds have been produced in Brazil, as well as quantities of pale-green beryl too light in color to be ethically called emerald. In 1913 emeralds were discovered in Bahia in an altered clolomitic marble associated with quartz and calcite; the locality name was Bam Jesus dos Meires. The pale color of these stones was such that the mine has never been exploited on any large scale.
Several new discoveries were made between 1960 and 1970. One, the Salininha district in Brazil, produced medium quality green stones colored by vanadium rather than chromium. For this reason, European gemologists refused to call them emeralds, even though they were deeper green and of better quality than some beryl colored by chromium. A second recent source, Carnaiba, produces probably the best emeralds in Brazil, but very few of them approach Colombian quality.
The most recent emerald discovery of importance occurred in Southern Rhodesia, Africa, in the Sandawana Valley. The discovery was made by two veteran prospectors, Lawrence Contat and Cornelius Osthuizen, who had been prospecting in Rhodesia since 1954 for beryl, tantalum and lithium ores, and other pegmatite minerals. Their efforts had centered in the Sabi Valley, in a remote part of Southern Rhodesia. They had discovered some deposits and had been mining on a small scale in that area, but their principal interest was in prospecting. Accordingly, they continued their search for further mineral deposits, concentrating on finding pegmatite dikes. Their interest in pegmatite led them to prospect an area four hundred miles to the south of their mining properties in a very remote and mountainous district. This was an area of very ancient (pre-Cambrian) schistose rocks, traversed in some areas by large pegmatite dikes. Within two days of their entry into the new region, Osthuizen discovered beryl in large quantities and a good sized deposit of spodumene, which is much in demand as a lithium ore. The two men started to examine a large pegmatite dike and soon discovered the first emeralds.
The stones were of low quality but they decided that they were worth investigating, so they searched the surrounding area. In October, 1955, within ten days after their arrival, they had discovered these first emeralds, but it was seven months later before they finally found a second deposit, this one important. Because their first camp had been at Sandawana, this name was applied to the emeralds, despite the fact that the discovery was made in an adjoining valley.
It is wild country, infested by crocodiles and rich in other wildlife. In the dry season, the scarcity of water and the distance from the nearest road and railroad pose serious problems. Pits dug below the outcrop show that the soil has been enriched by numerous emeralds left from the erosion and departure of the softer, less durable portions of the host rock through the ages. Most of the stones are very small, usually cutting to less than one quarter of a carat in size, although larger stones are sometimes obtained. In this small size, the color is magnificent; it is so intense that the stones are ideally suited for guard rings and other jewelry utilizing emerald calibre. For a number of years, there has been a dearth of emeralds with the necessary intensity of color to be useful for the production of calibre. Thus, the discovery in Rhodesia will provide a very important addition to gem sources.
There are a number of other sources of emerald. India produces stones from two localities, both discovered in the 1940's. The first came as an accidental discovery in the World War II search for beryl and mica in the Arawalli Mountains in Rajasthan; this was at Kaliguman in Udaipur. Initial mining efforts from the mica-schist by a Jaipur emerald dealer and his partner in 1945 were successful. Later, prospecting turned up deposits elsewhere in Udaipur and Ajmere-Merwara. The Rajgarh mine, fifteen miles south of Ajmere, started operations in a talc-biotite mica-schist in 1947.
Stones from this mine and elsewhere in the district are of a better average quality than those from Kaliguman. India has become more important as a source of emeralds since the later discoveries in Ajmere-Merwara. The Rajgarh mine is operated from a shaft from which drifts extend on a number of levels. The shaft operation has proved to be rather expensive, since excessive timbering is required to support the somewhat friable rock.
Some years ago, emeralds were discovered in the Transvaal, in the Union of South Africa where they occur in conjunction with a series of pegmatite dikes traversing ancient schists.
The mine is not too far from the Sandawana deposit. The Sandawana deposit is on the north side of the Murchison Range and the Transvaal deposit on the south. It is a small-scale, open-pit operation that is worked only spasmodically. The output is made up of a wide range of qualities, from almost colorless beryl to fine green material with few inclusions. Although the finer stones are of good quality, they do not compare with the more expensive grades of the South American production. The Rransvaal deposit which was discovered in 1927, has not had any great impact on the emerald market, because the general quality did not lead to a significant demand.
Other emerald sources include the Habachtal Valley, in the Austrian Alps; Western Australia and New South Wales; and Alexander Mitchell, Creve lend and Macon Counties, North Carolina. All of these sources are commercially unimportant.
Recently, however, in Hiddenite, North Carolina, a rough emerald crystal weighing approximately sixty carats was found, and subsequently fashioned into a richly colored 13.14 carat stone.
Aquamarine and Other Beryls
Aquamarine and the other beryls of gem quality are found almost exclusively in pegmatite dikes. The principal source today is the State of Minas Geraes, Brazil. Although varied in size and quality. Brazilian production usually tends toward rather light colors.
Another important producer for many years was the same general area of Russia from which Chrysoberyl was mined: in the vicinity of Sverdlovsk, on the east side of the Ural Mountains. This area produced a volume of beryls in all colors, including emerald. Production was sufficient to make Sverdlovsk a major cutting center.
Madagascar is also a source of significance. This island has been called "the country of beryls" for it produces fine gem material of unusually beauty. Its aquamarine has a color more akin to that of Ceylon sapphires than to other aquamarine, and its morganite is a rich purple-red color.
The step cut is so commonly used for emerald that this style is usually referred to as the emerald cut; this is particularly true if the stone is rectangular in shape with eight sides and three tiers of facets on top and three tiers on the bottom. A square stone of the same description is referred to as a square emerald cut. Heavily flawed stones are usually cut in cabochon or carved. Small stones are frequently cut into baguettes or calibre. The round brilliant cut is rarely used, since it does not show the color of an emerald to best advantage.
Aquamarine and the other beryls are not particularly sensitive to the heat generated by any phase of the fashioning process; emeralds, however, particularly heavily flawed stones, must be treated with care, since the flaws and fractures may develop further or the stone may break.
Cabochon material may be ground in the usual manner, using carborundum wheels and regular sanders for the preliminary operations. polishing is accomplished either on leather laps with Linde A polishing powder or on felt laps with cerium oxide. If the hollow tubes in cat's-eye material tend to pick up the abrasive or polishing agent, they may be sealed off by first dipping the stone in liquid shellac and then removing it with alcohol after the stone is finished.
Transparent material is ground on diamond impregnated laps. Polishing is accomplished on tin laps with Linde A powder. An alternative method is to use a Lucite lap with either cerium oxide or tin oxide as the polishing agent. Since emeralds are usually cut to exhibit the most attractive color, carful attention must be given to orientation of the attractive color. Suggested angles are 42° for the crown and 43° for the pavilion.
|Chemical Composition||A beryllium-aluminum silicate, expressed by the formula Be2Al2(SiO3)6|
|Crystallographic Character||Hexagonal system. Habit: usually, the simple prismatic form, more perfectly formed than most gem crystals. Crystals are sometimes modified and terminated by basal pinacoids.|
|Hardness||7 1/2 to 8|
|Toughness||Poor. Because it is usually flawed, often heavily, emerald should be given great care in handling, setting and cutting. The toughness of aquamarine and the other beryls is classed as good.|
|Cleavage||Very difficult; parallel to the basal plane of the crystal.|
|Specific Gravity||Emerald: 2.67 to 2.75; normal 2.71. Other beryls: 2.67 to 2.84. Morganite is usually 2.82|
|Characteristic Inclusions||Colombian emerald are characterized by three-phase inclusions; i.e. cavities containing a solid, a liquid and a gas. Calcite or pyrite are other minerals frequently found in emerald. The following illustrations show the expected types of inclusions found in beryl materials.|
|Degree of Transparency||Transparent to translucent.|
|Luster||Polished surface are vitreous; fracture surfaces are vitreous to resinous.|
|Refractive Index||Usually 1.577-1.583. May vary from a low of 1.565-1.570 to a high of 1.590-1.599.|
|Birefringence||0.005 to 0.009|
|Optic Character||Uniaxial negative.|
|Pleochroism||Emerald: strong green and blue-green. Aquamarine (blue): weak to distinct blue and light blue. Aquamarine (greenish blue): weak to distinct blue and blue-green. Golden: weak greenish yellow and yellow. Brown: weak brownish yellow and greenish yellow. Morganite: distinct light red and light violet .|
|Phenomena||Rarely, poor-quality star stones and cat's-eyes.|
|X-Ray Fluorescence||Emerald: very weak, dull red. Aquamarine: none. Colorless: none to pale yellowish or pinkish. Golden: none. Morganite: an intense crimson glow.|
|Transparency to X-Rays||Transparent|
|Ultraviolet Fluorescence||Emerald: none to weak orangey red to violetish red under long wavelength. Aquamarine: none. Colorless: none to pale yellowish or pinkish under both wavelengths. Golden: none. Morganite: weak, light red under both wavelengths.|
|Color-Filter Reaction||Emerald: red. Indian and Transval emeralds are exceptions, however, since they appear green through the filter. Aquamarine and other beryls: none.|
|Absorption Spectra||Emerald: distinct lines in the red at 6830 and 6805 A.U. Less distinct lines at 6620 and 6460 A.U. Partial absorption of the orange-yellow between 6300 and 5800 A.U. and almost completion absorption of the violet. Aquamarine: An indistinct line in the green and blue at 5370 and 4560A.U., respectively, as well as a strong line in the violet at 4270 A.U., depending on depth of color of the stone.|
Effects Caused by:
|Heat||Emerald: Fuses with difficulty before the blowpipe or jewelers torch. May cause additional fracturing or complete breakage of the stone. Heat must be avoided in cleaning, repairing, mounting and cutting. Aquamarine: Whitens and fuses with difficulty before the blowpipe or jewelers torch. The color of aquamarine may be improved by heating. Some green beryl becomes permanently blue.|
|Acids||Emerald and the other beryls are resistant to all acids except hydrofluoric.|
|Irradiation||When treated with the Van de Graaf generator, beryl acquires permanent coloration. The change is not entirely consistent and most stones are not economically promising, despite the persistence of color. Pale emeralds become somewhat grayish green and unattractive. One light-colored Brazilian specimen, when subjected to prolonged bombardment, became strongly dichroic (and shattered) in bluish violet
and gray-green. Most treated emeralds tend to revert to their original color after
exposure to a few minutes of sunlight, and then do not color so darkly with a second treatment. Some stones retain a little darkening but it is not an improvement, since the green color is no more attractive than before treatment.
A dark aquamarine became quite green when subjected to X-rays, but it was not an emerald green. It retained this color for several years, until it was heated rather drastically, whereupon it reverted to the original aquamarine blue. Before electrons the same thing happens: pale aquamarines and colorless beryls turn to pale golden beryls, but the depth of color, which experience has shown to vary from stone to stone, is never intense, and prolonged bombardment does nothing to change it after the first hour or so.
Stones exposed directly to the electron beam tend to crack badly. Prolonged exposure of the golden stones to sunlight does not seem to fade them; the color that persists after the first few minutes of exposure to light (and it may even fade somewhat in the dark within minutes of the treatment) resists anything but actual heating to remove it. Research has shown that pale beryls can be made golden in an atomic pile, but they retain the radioactivity.
Unquestionably, the materials that are most likely to be confused with emerald today are the synthetic emeralds of Chatham, and Linde, both of the United States, and the Gilson synthetic emerald produced in France. More than one test is usually required to effect a positive separation, but these tests generally are not particularly difficult to apply nor to interpret. Lower refractive indices, birefringence, and specific gravity in most synthetics, plus wispy inclusions, and fluorescence are the key tools of separation. Recent additional tests that prove helpful are the absorption spectra and transparency to X-rays.
The refractive index range of natural emerald may be as low as 1.565-1.570 (rare), to a high of 1.590-1.599 for the Sandawana material; however the usual R.I will be in the area of 1.577-1.583. Note that the birefringence can be as low as 0.005 to a high of 0.009, with the most common figure being 0.006. The indices of synthetic emerald vary, and special attention should be given to these readings. The Chatham synthetic emeralds give readings in the range of 1.561-1.565, whereas the Gilson may be as low, but often in the 1.564-1.569 area: both have a birefringence of 0.003 to 0.005. Some Gilson emeralds however, give readings as high as 1.571-1.579 with a birefringence of 0.008. The Linde Hydro thermals give readings as low as 1.566-1.571, and as high as 1.572-1.578, with a birefringence of 0.005 to 0.006. Most today are near the higher end in indices and birefringence.
The specific gravity of natural emerald ranges from a low of 2.67 to a high of 2.75, with a normal of 2.71. A specific gravity liquid set at 2.67 is often helpful in separating most natural emeralds from the Chatham synthetics and a few others. The specific gravity of the Chatham synthetic emerald is usually constant at 2.66. Most Gilson synthetic emeralds have a specific gravity in the range of 2.65-2.66, but some may have a density as high as 2.68-2.69. The Linde Hydrothermal has a density of 2.67-2.69.
Prior to recent discoveries, a helpful test in the separation of natural and synthetic emeralds was fluorescence under long-wave ultraviolet light. Natural emeralds are most often inert, or may exhibit a weak orangey-red to violetish-red. However, there is now a group of Gilson synthetics that are also inert, and as all the other types of synthetic emeralds are known to exhibit characteristic fluorescence, care must be used in application of this test. Under long-wave ultraviolet light, the Chatham's fluoresce brick red, certain groups of Gilson's vary from a strong orangey-red to red, and the Linde Hydrothermals a strong red.
Another test that is no longer reliable for separating natural from synthetic emeralds is the transparency to short-wave ultraviolet, since in both, opaque and transparent reactions are encountered. Also, when testing for transparency to X-rays, both naturals and most synthetics are transparent with the exception of the group of non fluorescent Gilson's. When tested with X-ray, these stones are opaque. The opaqueness of this group of Gilson's is apparently due to the addition of Iron which also accounts for its lack of fluorescence, and its increased refractive index and specific gravity. The presence of iron also gives this stone a characteristic absorption spectrum with a line at 4270 A.U., and makes testing with the spectroscope very important in its identification.
The inclusions in flux melt synthetic emerald are sometimes confusing natural appearing at first glance. These inclusions are made up of solid flux, usually distributed in a veil-like or wisplike pattern. Phenakite crystals and platinum crystals are often present. Zoning is quite common and these zonal lines may be straight or angular in conformity to the hexagonal prism. The hydrothermal material may also contain clear crystals of the beryllium mineral phenakite, often with long, thin, cone shaped spaces extending from them. The Chatham synthetic often contains crystals of platinum, with a white, cubic appearance. The source of the platinum is thought to be the makers vessel. In contrast, natural emeralds often show three-phase inclusions irregular spaces or cavities containing a liquid, a gas bubble, and a tiny, flat platelike crystal. (In Colombian emeralds the crystal in the three-phase inclusion appears square or rectangular in shape, but must be resolved under at least twenty magnification.) Natural stones may also contain calcite, actinolite, or mica plates or slender tremolite crystals. Nothing closely resembling these inclusions are found in the synthetic. Metallic inclusions of pyrite with a brass-yellow to golden-yellow cubic appearance are also another possibility in the natural stone.
In 1961, an additional synthetic appeared in America that had been known as the Lechleitner product. For a short time before the development of the Linde synthetic emerald, this was handled by the Linde Company. It is a perfected beryl with an overgrowth of synthetic emerald. The resulting stone bears a resemblance to a pale natural emerald. The synthetic layer has properties more nearly similar to those of the natural than the Chatham synthetic, but it is detected readily by the presence of long, thin, roughly parallel cracks that extend from the surface through the overgrowth layer. When immersed in liquid, the outer layer of synthetic emerald is usually clearly visible. Under long-wave ultraviolet, the synthetic emerald coating will fluoresce a weak orange to red, the intensity depending upon the thickness of the coating. The most intense fluorescence is usually seen in the girdle area.
Of interest to the manufacturing jeweler and of academic interest to the gem-tester, is the report by Chatham that the synthetic emerald is supposed to withstand heating to a red heat without damage, whereas the natural usually shatters under this treatment. Tests made by the GIA, however, proved differently. A natural and a synthetic crystal of equal size were placed on a charcoal block and heated to the same temperature. Both cracked internally after cooling from a red heat but neither shattered, although the natural stone became quite cloudy, and the synthetic resumed its original green color.
Synthetic emerald is so expensive, compared with other synthetics (and, as a matter of fact, with many natural stones), that there is still a demand for other kinds of substitutes that are seldom, if ever, made today as substitutes for other gemstones . For example, triplets (the so-called Soude emeralds) consisting of two pieces of beryl, quartz or synthetic corundum or spinel. Excellent imitations of emerald were also made at one time with garnet-and-glass doublets. A triplet is rather easily detected merely by immersing it in water and examining it parallel to the girdle. In this manner, the colorless or nearly colorless crown and pavilion and the green cement become obvious. (Caution: Immersion in bromoform or methylene iodide may destroy the green color of the cement) Usually, the nature of the substitute is also visible under magnification. If a beryl top and bottom are used of course, the stone will have the same R.I. as a natural emerald; therefore, immersion would be necessary to detect it. The true nature of the piece is particularly likely to be overlooked if it is mounted. Most assembled imitations of emerald have been found to be quartz and quartz triplets. Fused beryl-and-glass doublets have also been offered for sale recently.
Light-colored beryls are frequently set in gypsy-type mountings, either in rings or other forms of jewelry. Such stones may be made to appear much better by the presence of a green foil or a green cement on the pavilion. It is usually possible to detect this added color in a mounted stone in one of two ways. If examination is made in a manner in which enough light is directed at one side of the stone, so that it is possible to use the dichroscope to analyze the light emerging from the stone, the characteristically strong dichroism of emerald will be missing. Weak dichroism mayor may not be evident, however, if the stone has a light color and the color that is seen is the result of the foil backing. By illuminating the stone in the same manner and examining the emerging light with a spectroscope, the absorption bands that one would expect in emerald because of the chromic-oxide coloring agent (especially those bands in the red) would identify the stone as an emerald and the color as genuine, rather than induced by foil.
Unfortunately, emeralds are often "oiled" on the excuse given by some dealers that it is necessary to "restore the natural oils lost in cutting" This is possible only when cracks extend to the surface. Usually, the stone paper or the cloth liner in the paper in which unmounted stones are carried is stained by the oil. An examination of the cracks under magnification usually reveals the coloring agent. It may be bolted out usually, but liquid plastic may be used for this purpose to prevent the boiling from removing the color. A more reliable test of oiled stones involves the use of long-wave ultraviolet light on the suspected stone. If oiled, the treated cracks will fluoresce a pale yellowish.
One of the tests frequently applied to emerald is the use of the emerald filter. This filter is designed so that light is largely absorbed, except in a portion of the red and yellow-green part of the spectrum. Since the emerald absorbs that portion of the yellow-green, the light that passes through an emerald will appear to be red through the filter, in contrast to most emerald imitations. There is, however, no significant difference, in the synthetic and most natural emeralds. Most other green stones, on the other hand, will appear green through the filter. Natural Indian and Transvaal emeralds will appear green also. On occasion, emeralds are encountered that give a satisfactory red reaction but that on close inspection under magnification are seen to be coated. The coating is a colored plastic that gives the same color-filter reaction as that of emerald. Not only are bubbles usually evident in this surface layer, but its softness permits it to be scratched or removed easily. Sometimes, however, a dealer will be deceived by one of these beautifully colored stones and buy them at a price consistent with the depth of color. It is only later that the coating becomes evident and the dealer realizes that he has been cheated. A number of quartz triplets have been encountered in which the green cement layer shows red under the color filter, thus further minimizing the effectiveness of this instrument with emerald.
Other natural stones that resemble emerald in appearance can be separated readily from it by physical properties. These include tourmaline, peridot, demantoid and green zircon. Each of these stones sinks in a specific-gravity liquid of 2.89 (bromoform), whereas emerald floats; furthermore, each has an R.I. range considerably above that of emerald, with zircon and demantoid being above the scale of the refractometer. Tourmaline's R.I. is approximately .04 to .06 higher than most emerald, and peridot is about .05 to .11 higher; in addition, both have much greater birefringence. None of these stones has a really convincing emerald color.
Excellent glass imitations of emerald are made, some of which contain inclusions that resemble those of the natural. Glass with numerous bubbles is occasionally treated in a manner just before hardening that tends to elongate the bubbles and give them a needle like appearance to the casual observer. Sometimes, a material is added that does not melt the same temperature as glass and simulates the appearance of the inclusions in emerald. The R.I. and S.G. of emerald may be duplicated in glass. In this event, it is necessary to resort to the dichroscope or polariscope, for glass is singly refractive and emerald is doubly refractive.
Of the other beryls, a number may be confused with other natural stones of similar appearance and/or properties. Although the physical properties of blue topaz are considerably different, its close resemblance to aquamarine often causes confusion in identification. The R.I. of topaz is usually about two points above 1.69, whereas that of aquamarine is .02 below. A careless reading may therefore lead to an error in identification. This kind of testing mistake is not made frequently; nevertheless, carelessness is an ever-present specter to the tester. Synthetic spinel and tourmaline may resemble either morganite or aquamarine, and zircon looks similar to aquamarine. All of these stones can be separated readily by a refractive-index reading or examination under magnification. The birefringence of tourmaline and zircon is much too strong to be confused with beryl. Synthetic spinel not only often contains bubbles, but it is obviously singly refractive; moreover, blue synthetic spinel turns red under the color filter.
One of the common difficulties encountered by novice testers is distinguishing between yellow beryl and yellow quartz; this can result from a carelessly taken R.I. reading. Since the optic sign of quartz is positive, it gives the usual reading of 1.544; beryl, being negative in sign, gives the usual reading of a high index, or, for yellow beryl, usually about 1.57 or 1.575. Thus, there is a distinct difference in index between the two when the reading is taken in white light under ordinary conditions. Moreover, although the S.G. of the two is similar, beryl will sink in the emerald liquid and quartz will float.
Two unusual gemstones with which beryl may be confused are yellow, transparent labradorite and pink or other colors of scapolite, Labradorite has indices of approximately 1.555 to 1.565 and an S.G. of about 2.70. Careful testing will show that it is biaxial, whereas beryl is uniaxial. Labradorite possesses two directions of easy cleavage, which may be apparent under magnification. Also, it is slightly lower in index and both indices vary, in contrast to the constant high index and variable low index of beryl. Scapolite, which is especially likely to be confused with morganite, has indices of 1.55 to approximately 1.57. The fact that one of the readings is in the 1.57 region could lead one taking a reading in only one position to believe that the stone is beryl. However, the low (.006) birefringence of beryl contrasts with the figure for scapolite, which is near .020. Thus, doubling of back facet junctions in scapolite is fairly strong.
In order to merit the top-quality designation, an emerald must be an intense, medium-dark tone of slightly yellowish or bluish green and have a velvety ("soft") body appearance and a minimum of flaws. Stones of this superfine quality are exceedingly rare; in fact, much less than one percent of the material found can be classed in this grade. In Size of two and three carats and larger, they may exceed the price of diamonds of the same weight and quality. Since emeralds have no fire and less brilliancy than most gems, beauty of color and its distribution are prime factors in determining value. Stones in which lighter and darker portions are arranged irregularly or in layers are much less desirable than those that are evenly colored.
Also, too heavily flawed or "mossy" gems are not desirable. Usually (and ironically), the better the color the less perfect the stone. Light to medium-light tones are much less valuable, even when slightly flawed or nearly flawless; these qualities in size up to five carats are not difficult to obtain. The fact that the finest vivid green and velvety body appearance of emerald occurs in no other transparent stone contributes greatly to its value. Among the important natural gems, jade alone approaches this color, and glass and synthetic emerald are the only manmade materials that imitate it closely.
Unlike emerald, clear aquamarine crystals of great size are often found; therefore, large, flaw less stones are comparatively easy to obtain. Fine greenish-blue gems are the most characteristic of top-quality aquamarines, although the so-called Madagascar blue is considered by many dealers as the most valuable. The price of fine medium and medium-dark stones has increased materially in recent years. These desired tones in flaw less quality are quite rare. The lighter tones, however, can be obtained easily and in almost any size range.
The darker specimens of morganite and golden beryl are scarce and sell quickly to collectors. Colorless beryls are plentiful but have little value.