Emerald is the name given to beryl of a pure and intense green colour; the particular shade of colour seen in this variety of beryl is often alluded to in ordinary language as emerald-green, but emeralds may be also grass-green, green tinged with yellow, or celadon-green tinged with grey. Beryls of a bluish-green colour are not included in this variety. Many specimens of emerald are very pale in colour, varying in intensity down to greenish-white; these are, however, not cut as gems; only those of a beautiful and deep emerald-green to grass-green are highly prized. The particular shade of green characteristic of the emerald is almost unrivalled in depth and brilliancy, and is often compared to the fresh green of a meadow in spring. The finest stones possess a peculiar velvety lustre, like that shown by some dark blue sapphires.
According to F. Wöhler, the colour of emerald from Muzo in Colombia probably depends upon the presence of chromic oxide, 0.186 per cent. of this substance having been found in the specimen examined by Wöhler. That the deep green of the emerald can be produced by so small an amount of chromic oxide has been proved by fusing white glass with the same percentage of this metallic oxide, a glass having the intense green of the finest emeralds being produced. More recently it has been shown that the colouring-matter of Uralian and Egyptian emeralds also is due to chromic oxide.
Emeralds of good, full colour are distinctly dichroïc; the images shown by the dichroscope are respectively emerald or yellowish-green and bluish-green. The colour of the emerald is not always distributed uniformly through its substance. The differently coloured portions may occur irregularly or in layers; in the latter case the layers are, as a rule, parallel to the basal plane of the crystal, that is to say, perpendicular to the prism faces.
The transparency of the emerald is perfect only in rare cases. The majority of crystals are rendered cloudy and dull, not only by fissures and cracks, but also by the presence of microscopic enclosures, which in places are accumulated in large numbers. These enclosures may be fluid or solid, scales of mica being especially common. Cloudy and opaque crystals of emerald are usually dull in colour, approaching the characters of common beryl and being useless for cutting as gems. Perfectly clear and transparent stones are naturally the most valuable, but fissured and cloudy specimens, provided they possess the fine emerald-green colour, have a certain value.
Compared with other precious stones, the rarity of perfect specimens of emerald is unique. The most common faults are those, which have been just mentioned, fissures being almost invariably present. Stones, which are clouded by fissures, are described as "mossy". Irregularities in the distribution of colour, and dull and cloudy patches, are also frequently to be seen.
The disparity between the value of a perfect and of an imperfect emerald is enormous. A faultless emerald is worth as much, or nearly as much, as a ruby, and certainly more than a diamond. A one-carat stone, perfect in colour and transparency, is worth at least $2,200 and large stones, on account of their rarity, have a value out of all proportion to their size. As a matter of fact, a perfect emerald weighing but a few carats is so rare that almost any price will he given for it by collectors. Fissured stones, which are cloudy but of good colour, are much cheaper; when the colour is pale they are worth no more than $550 or even $275 per carat. The value of such stones is more or less proportional to their size, large stones of this description being by no means uncommon.
Flawless emeralds of large size are extremely rare, so that only small stones are available for cutting as gems. Emeralds of considerable size have been known, but their quality leaves much to be desired; moreover, in the case of large stones found and described in early times, it must be remembered that the name emerald was applied to other stones of a green colour. The ancient Peruvians are said to have numbered among their deities an emerald the size of an ostrich's egg. Again, there was reported to be in the treasury at Vienna an emerald which weighs 2,205 carats, while Schrauf states that in the same place is preserved an ink-well cut out of a single stone, besides other large emeralds cut as table-stones. One of the largest and finest emeralds known belonged to the Duke of Devonshire. It is a natural crystal of the form characteristic of emerald, namely, a hexagonal prism with a basal plane. This stone measures 2 inches across the basal plane, and weighs 8 9/10 ounces or 1,350 carats; it is of the finest colour, clear and transparent, and almost faultless. This stone came from the emerald mines at Muzo in Colombia, where crystals of the length and thickness of a finger are by no means rare. Crystals of equal size are found in the Urals and are not specially rare; one measuring 8 inches in length and 5 inches in diameter is presented in the collection of the Imperial Institute of Mines in St. Petersburg, and still larger crystals have been reported. Probably the largest was in the possession of the Czar of Russia; it is said to measure 25 centimetres (nearly 10 inches) in length and l2 centimetres in diameter. One or two very large stones, formerly thought to be emeralds, have on closer examination proved to be green glass; such, for example, is one weighing 28 3/4 pounds in the Reichenau monastery above Chur, in the Rhine Valley, Switzerland.
The form in which an emerald is cut depends upon the character of the rough stone. Perfectly faultless, transparent fragments, when not too dark, are cut as brilliants or as rosettes. Most frequently, however, the step-cut with brilliant facets on the upper portion is adopted. The emerald, though not infrequently cut as a simple table-stone, is probably never, at least in Europe, cut en cabochon. Cut gems, perfect in colour and transparency, are mounted à jour; paler stones are provided with a green foil placed beneath them, while fissured or otherwise faulty stones are mounted in a closed setting blackened inside.
Natural crystals of emerald are, as a rule, too large and too much flawed to be cut as single gems; they are, therefore, sawn into portions of suitable size and purity, great care being taken to avoid unnecessary loss of material. In many crystals, clear and transparent portions suitable for gems have to be cut out of the main mass of the crystal, and in this operation special care is required. Each portion so cut out of a crystal is faceted in the form best suited to its particular shape.
Compared with the precious stones hitherto considered, the emerald, in its mode of occurrence, is unique, for it is found exclusively in its primary situation, that is to say, in the rock in which it was formed. It is one of the minerals characteristics of crystalline schists, and in many places is found embedded in mica-schists and similar rocks. The famous occurrence at Muzo in Colombia is the only exception to this rule, the emerald being here embedded in calcite veins in limestone. This occurrence has called forth the perfectly groundless supposition that the emeralds here were originally formed in crystalline schists and were afterwards deposited in the calcite veins. The emerald practically never occurs in gem-gravels, in the way in which diamonds, rubies, etc., occur.
The earliest known emerald locality is doubtless that in Upper Egypt, not far from the coast of the Red Sea and south of Kosseir. Though the ancients knew the occurrence of emerald in Ethiopia, the locality, in course of time, became completely forgotten, and ancient accounts of the occurrence were regarded as erroneous. It has been supposed that true emeralds were first introduced into Europe at the end of the sixteenth century from South America; they had been found previously, however, both with Egyptian mummies and also among the ruins of the two Roman cities, Herculaneum and Pompeii. These latter, which were discovered long before the end of the sixteenth century (1566), could not have been brought from South America, the most important locality at the present day, but probably came from Egypt or, as also mentioned in ancient writings, from Scythian lands, and thus perhaps from the Urals, where they are still found.
The ancient Egyptian mines were re-discovered in the second decade of the nineteenth century by Cailliaud, a member of the expedition organized by Mehemet Ali Pasha; they have been frequently visited since by European travellers. The workings were partly surface and partly underground, the timbering of the latter being frequently found in a well-preserved state. The deposit was worked to a considerable extent, some of the mines being large enough to admit of 400 men working together at the same time. The facts, which led these ancient miners to suspect the existence of emeralds in these deposits, and the date at which the workings were commenced, are alike unknown. The appliances and tools, which have been found in the mines, date back to the time of Sesostris (1,650 B.C.). It is recorded in ancient inscriptions that, in the time of Alexander the Great, Greek miners were employed in these mines; and it is evident that they were worked during the reign of Cleopatra, for emeralds bearing an engraving of herself were used for presentation by this queen. There is no subsequent record of the mines until their re-discovery by Cailliaud, who, with the permission of Mehemet Ali, re-opened them in 1819, the actual work being performed by Albanian miners. Perhaps on account of the poorness of quality of the stones the work was soon abandoned, and apparently with great suddenness, for a number of baskets filled with material ready to be drawn up to the surface have been discovered in the mine just as they were left by the Albanian miners.
These ancient mines are situated in a depression of the long range of mountains which borders the west coast of the Red Sea; in the same range are to be found gold and topaz mines. The emerald mines are in two groups, one being known as the Jebel (= Mount) Sikait (also called Sakketto), and the other, about ten miles to the north, as the Jebel Sabara (Zabara, Zubara, etc.), both being It little south of latitude 25° N. The most important and extensive of the two groups of mines is that of the Jebel Sikait; it is connected with the Red Sea fifteen miles to the east by the Wadi Chamal and judging from the ruins of houses, temples, and other buildings which are still to be found there, must have been the site of a town of no inconsiderable size. Hundreds of shafts of various depths have been driven into the hill, which is 600 to 700 feet in height. Mr. D. A. MacAlister has in 1899 again visited these so-called Cleopatra's emerald mines with the view of re-working the old mines. The ancient workings on the Jebel Sabara are similar, but less extensive.
Diamond Diamond Geology and Mining Diamond Trade
Rafal Swiecki, geological engineer email contact
This document is in the public domain.