Gems - Beryl - Emerald, Aquamarine, Morganite
( Originally Published 1919 )
THE species to be considered in this chapter includes the varieties emerald and aquamarine, as well as what jewellers understand by beryl. It has many incontestable claims on the attention of all lovers of the beautiful in precious stones. The peerless emerald (Plate I, Fig. 5), which in its verdant beauty recalls the exquisite lawns that grace the courts and quadrangles of our older seats of learning, ranks today as the most costly of jewels. Its sister stone, the lovely aquamarine (Plate I, Fig. 4), which seems to have come direct from some mermaid's treasure-house in the depths of a summer sea, has charms not to be denied. Pliny, speaking of this species, truly says, " There is not a colour more pleasing to the eye " ; yet he knew only the comparatively inferior stones from Egypt, and possibly from the Ural Mountains. Emeralds are favourite ring-stones, and would, no doubt, be equally coveted for larger articles of jewellery did not the excessive cost forbid, and nothing could be more attractive for a central stone than a choice aqua-marine of deep blue-green hue. Emeralds are usually step-cut, though Indian lapidaries often favour the en cabochon form ; aquamarines, on the other hand, are brilliant-cut in front and step-cut at the back.
Beryl, to use the name by which the species is known to science, is essentially a silicate of aluminium and beryllium corresponding to the formula, Be3Al2 (S103)6. The beryllia is often partially replaced by small amounts of the alkaline earths, caesia, potash, soda, and lithia, varying from about 1 1/2 per cent. in beryl from Mesa Grande to nearly 5 in that from Pala and Madagascar, and over 6, of which 3.6 is caesia, in beryl from Hebron, Maine ; also, as usual, chromic and ferric oxides take the place of a little alumina ; from 1 to 2 per cent, of water has been found in emerald. The element beryllium was, as its name suggests, first discovered in a specimen of this species, the discovery being made in 1798 by the chemist Vauquelin ; it is also known as glucinum in allusion to the sweet taste of its salts.
When pure, beryl is colourless, but it is rarely, if ever, free from a tinge of blue or green. The colour is usually some shade of green—grass-green, of that characteristic tint which is in consequence known as emerald-green, or blue-green, yellowish green (Plate I, Fig. 6), and sometimes yellow, pink, and rose-red. The peculiar colour of emerald is supposed to be caused by chromic oxide, small quantities of which have been detected in it by chemical analysis ; moreover, experiment shows that glass containing the same percentage amount of chromic oxide assumes the same splendid hue. Emerald, on being heated, loses water, but retains its colour unimpaired, which cannot therefore be due, as has been suggested, to organic matter. The term aquamarine is applied to the deep sea-green and blue-green stones, and jewellers restrict the term beryl to paler shades and generally other colours, such as yellow, golden, and pink, but Kunz has recently proposed the name morganite to distinguish the beautiful rose beryl such as is found in Madagascar. The varying shades of aquamarine are due to the influence of the alkaline earths modified by the presence of ferric oxide or chromic oxide ; the beautiful blushing hue of morganite is no doubt caused by lithia.
The name of the species is derived from the Greek Bnpunnos, an ancient word, the meaning of which has been lost in the mists of time. The Greek word denoted the same species in part as that now under-stood by the name. Emerald is derived from a Persian word which appeared in Greek as ouapaydos, and in Latin as smaragdus ; it originally denoted chrysocolla, or similar green stone, but was transferred upon the introduction of the deep-green beryl from Upper Egypt. The name aquamarine was suggested by Pliny's exceedingly happy description of the stones " which imitate the greenness of the clear sea," although it was not actually used by him. That emerald and beryl were one species was suspected by Pliny, but the identity was not definitely established till about a century ago. Morganite is named after John Pierpont Morgan.
The natural crystals have the form of a six-sided prism, and in the case of emerald (Fig. 70, and Plate I, Fig. 8) invariably, if whole, end in a single face at right angles to the length of the prism ; aquamarines have in addition a number of small inclined faces, and stones from both Russia and Brazil often taper owing to the effects of corrosion. The sixfold character of the crystalline symmetry necessarily entails that the double refraction, which is small in amount, 0.006, is uniaxial in character, and, since the ordinary is greater than the extraordinary refractive index, it is negative in sign. The values of the indices range between 1.567 and V590, and V572 and V598 respectively, in the two cases, the pink beryl possessing the highest values. The dichroism is distinct in the South American emerald, the twin colours being yellowish and bluish green, but otherwise is rather faint. The specific gravity varies between 2.69 and 2.79, and is therefore a little higher than that of quartz. If, therefore, a beryl and a quartz be floating together in a tube containing a suitable heavy liquid, the former will always be at a sensibly lower level (cf. Fig. 32). The hardness varies from 7 1/2 to 8, emerald being a little softer than the other varieties. There is no cleavage, but like most gem-stones beryl is very brittle, and can easily be fractured. Stones rendered cloudy by fissures are termed ` mossy.' When heated before the blowpipe beryl is fusible with difficulty ; it resists the attack of hydrofluoric acid as well as of ordinary acids.
In all probability the whole of the emeralds known in ancient times came from the so-called Cleopatra emerald mines in Upper Egypt. For some reason they were abandoned, and their position was so completely lost that in the Middle Ages it was maintained that emeralds had never been found in Egypt at all, but had come from America by way of the East. All doubts were set at rest by the re-discovery of the mines early last century by Cailliaud, who had been sent by the Viceroy of Egypt to search for them. They were, however, not much worked, and after a few years were closed again, and were re-opened only about ten years ago. The principal mines are at Jebel Zabara and at Jebel Sikait in northern Etbai, about 10 miles (16 km.) apart and distant about 15 miles (24 km.) from the Red Sea, lying in the range of mountains that run for a long distance parallel to the west coast of the Red Sea and rise to over 1800 feet (550 m.) above sea-level. There are numerous signs of considerable, but primitive, workings at distinct periods. Both emeralds and beryls are found in micaceous and talcose schists. The emeralds are not of very good quality, being cloudy and rather light in colour. Finer emeralds have been found in a dark mica-schist, together with other beryllium minerals, chrysoberyl and phenakite, and also topaz and tourmaline on the Asiatic side of the Ural Mountains, near the Takowaja River, which flows into the Bolshoi Reft River, one of the larger tributaries of the Pyschma River, about fifty miles (80 km.) east of Ekaterinburg, a town which is chiefly concerned with the mining and cutting of gem-stones. The mine was accidentally discovered by a peasant, who noticed a few green stones at the foot of an uprooted tree in 1830. Two years later the mine was regularly worked, and remained open for twenty years, when it was closed. It has recently been re-opened owing to the high rates obtaining for emeralds. Very large crystals have been produced here, but in colour they are much inferior to the South American stones ; small Siberian emeralds, on the other hand, are of better colour than small South American emeralds, the latter being not so deep in tint. Emeralds have been found in a similar kind of schist at Habachtal, in the Salzburg Alps. About thirty years ago well-formed green stones were discovered with hiddenite at Stony Point, Alexander County, in, North Carolina, but not much gem material has come to light
The products of none of the mines that have just been mentioned can on the whole compare with the beautiful stones which have come from South America. At the time when the Spaniards grimly conquered Peru and ruthlessly despoiled the country of the treasures which could be carried away, immense numbers of emeralds—some of almost incredible size—were literally poured into Spain, and eventually found their way to other parts of Europe. These stones were known as Spanish or Peruvian emeralds, but in all probability none of them were actually mined in Peru. Perhaps the most extraordinary were the five choice stones which Cortez presented to his bride, the niece of the Duke de Bejar, thereby mortally offending the Queen, who had desired them for herself, and which were lost in I 529 when Cortez was shipwrecked on his disastrous voyage to assist Charles v at the siege of Algiers. All five stones had been worked to divers fantastic shapes. One was cut like a bell with a fine pearl for a tongue, and bore on the rim, in Spanish,
Blessed is he who created thee." A second was shaped like a rose, and a third like a horn. A fourth was fashioned like a fish, with eyes of gold. The fifth, which was the most valuable and the most remarkable of all, was hollowed out into the form of a cup, and had a foot of gold ; its rim, which was formed of the same precious metal, was engraved with the words, " Inter natos mulierum non surrexit major." As soon as the Spaniards had seized nearly all the emeralds that the natives had amassed in their temples or for personal adornment, they de-voted their attention to searching for the source of these marvels of nature, and eventually in 1558 they lighted by accident upon the mines in what is now the United States of Colombia, which have been worked almost continuously since that time. Since the natives, who naturally resented the gross injustice with which they had been treated, and penetrated the greed that prompted the actions of the Spaniards, hid all traces of the mines, and refused to give any information as to their position, it is possible that other emerald mines may yet be found. The present mines are situated near the village of Muzo, about 75 miles (120 km.) north-northwest of Bogota, the capital of Colombia. The emeralds occur in calcite veins in a bituminous limestone of Cretaceous age. The Spaniards formerly worked the mines by driving adits through the barren rock on the hillsides to the gem-bearing veins, but at the present day the open cut method of working is employed. A plentiful supply of water is available, which is accumulated in reservoirs and allowed at the proper time to sweep the debris of barren rock away into the Rio Minero, leaving the rock containing the emeralds exposed. Stones, of good quality, which are suited for cutting, are locally known as canutillos, inferior stones, coarse or ill-shaped, being called morallons.
Emerald, unlike some green stones, retains its purity of colour in artificial light ; in fact, to quote the words of Pliny, " For neither sun nor shade, nor yet the light of candle, causeth to change and lose their lustre." Many are the superstitions that have been attached to it. Thus it was supposed to be good for the eyes, and as Pliny says, "Besides, there is not a gem or precious stone that so fully possesseth the eye, and yet never contenteth it with satiety. Nay, if the sight hath been wearied and dimmed by intentive poring upon anything else, the beholding of this stone doth refresh and restore it again." The idea that it was fatal to the eyesight of serpents appears in Moore's lines:
"Blinded like serpents when they gaze Upon the emerald's virgin blaze."
The crystals occur attached to the limestone, and are therefore never found doubly terminated. The crystal form is very simple, merely a hexagonal prism with a flat face at the one end at right angles to it. They are invariably flawed, so much so that a flawless emerald has passed into proverb as unattainable perfection. The largest single crystal which is known to exist at the present day is in the possession of the Duke of Devonshire (Fig. 71). In section it is nearly a regular hexagon, about 2 inches (51 mm.) in diameter from side to side, and the length is about the same ; its weight is 27&79 grams (9 3/4 oz. Av., or 1347 carats). It is of good colour, but badly flawed. It was given to the Duke of Devonshire by Dom Pedro of Brazil, and was exhibited at the Great Exhibition of 1851. A fine, though much smaller crystal, but of even better colour, which weighs 32'2 grams (156 carats), and measures t inch (28 mm.) in its widest cross-diameter, and about the same in length, was acquired with the Allan-Greg collection by the British Museum, and is exhibited in the Mineral Gallery of the British Museum (Natural History). The finest cut emerald is said to be one weighing 30 carats, which belongs to the Czar of Russia. A small, but perfect and flawless, faceted emerald, which is set in a gold hoop, is also in the British Museum (Natural History). It is shown, without the setting, about actual size.
The ever great demand and the essentially restricted supply have forced the cost of emeralds of good quality to a height that puts large stones beyond the reach of all but a privileged few who have purses deep enough. The rate per carat may be anything from L15 upwards, depending upon the purity of the colour and the freedom from flaws, but it increases very rapidly with the size, since flawless stones of more than 4 carats or so in weight are among the rarest of jewels ; a perfect emerald of 4 carats may easily fetch L1600 to £2000. It seems anomalous to say that it has never been easier to procure fine stones than during recent years, but the reason is that the high prices prevailing have tempted owners of old jewellery to realize their emeralds. O. the other hand, pale emeralds are worth only a nominal sum.
The other varieties of beryl are much less rare, and, since they usually attain to more considerable, and sometimes even colossal, size, far larger stones are obtainable. An aquamarine, particularly of good deep blue-green colour, is a stone of great beauty, and it possesses the merit of preserving its purity of tint in artificial light. It is a favourite stone for pendants, brooches, and bracelets, and all purposes for which a large blue or green stone is desired. The varying tints are said to be due to the presence of iron in different percentages, and possibly in different states of oxidation. Unlike emerald, the other varieties are by no means so easily recognized by their colour. Blue aquamarines may easily be mistaken for topaz, or vice versa, and the yellow beryl closely resembles other yellow stones, such as quartz, topaz, or tourmaline. Stones which are colourless or only slightly tinted command little more than the price of cutting, but the price of blue-green stones rapidly advances with increasing depth of tint up to £2 a carat: The enormous cut aquamarine which is exhibited in the Mineral Gallery of the British Museum (Natural History), affords some idea of the great size such stones reach ; a beautiful sea-green in colour, it weighs 179.5 grams (875 carats), and is table-cut with an oval contour.
The splendid six-sided columns which have been discovered in various parts of Siberia are among the most striking specimens in any large mineral collection. The neighbourhood of Ekaterinburg in the Urals is prolific in varieties of aquamarine ; especially at Mursinka have fine stones been found, in association with topaz, amethyst, and schorl, the black tourmaline. Good stones also occur in conjunction with topaz at Miask in the Government of Orenburg. It is found in the gold-washings of the Sanarka River, in the Southern Urals, but the stones are not fitted for service as gems. Magnificent blue-green and yellow aquamarines are associated with topaz and smoky quartz in the granite of the Adun-Tschilon Mountains, near Nertschinsk, Transbaikal. Stones have also been found at the Urulga River in Siberia. Most of the bluish-green aquamarines which come into the market at the present time have originated in Brazil, particularly in Minas Novas, Minas Geraes, where clear, transparent stones, of pleasing colour, in various shades, are found in the utmost profusion ; beautiful yellow stones also occur at the Bahia mines. Aquamarine was obtained in very early times in Coimbatore District, Madras, India, and yellow beryl comes from Ceylon. Fine blue crystals occur in the granite of the Mourne Mountains, Ireland, but they are not clear enough for cutting purposes ; similar stones are found also at Limoges, Haute Vienne, France. Aquamarines of various hues abound in several places in the United States, among the principal localities being Stoneham in Maine, Haddam in Connecticut, and Pala and Mesa Grande in San Diego County, California. The last-named state is remarkable for the numerous stones of varying depth of salmon-pink that have been found there. It is, however, surpassed by Madagascar, which has recently produced splendid stones of perfect rose-red tint and of the finest gem quality, some of them being nearly 100 carats in weight. These stones, which have been assigned a special name, morganite (cf. supra), are associated with tourmaline and kunzite. Pink and yellow beryls and deep blue-green aqua-marines occur in the island in quantity. The pink beryls from California are generally pale or have a pronounced salmon tint, and seldom approach the real rose-red colour of morganite; one magnificent rose-red crystal, weighing nearly 9 lb. (4.05 kg.), has, however, been recently discovered in San Diego County, California, and is now in the British Museum (Natural History). Blue-green beryl, varying in tint from almost colourless to an emerald-green, occurs with tin-stone and topaz about 9 miles (14 km.) northeast of Emmaville in New South Wales, Australia.
Probably the largest and finest aquamarine crystal ever seen was one found by a miner on March 28, 1910, at a depth of 15 ft. (5 m.) in a pegmatite vein at Marambaya, near Arassuahy, on the Jequitinhonha River, Minas Geraes, Brazil. It was greenish blue in colour, and a slightly irregular hexagonal prism, with a flat face at each end, in form; it measured 19 in. (48.5 cm.) in length and 16 in. (41 cm.) in diameter, and weighed 243 lb. (1105 kg.); and its transparency was so perfect that it could be seen through from end to end (Plate XXVI). The crystal was transported to Bahia, and sold for $25,000 (£5133).