PRECIOUS STONES

AQUAMARINE "AQUAMARINE-CHRYSOLITE" GOLDEN BERYL

Whenever possible, I provide, in parentheses, today's equivalent prices in US dollars. These prices take account of inflation and are based on available historical exchange rates. The inflation rate is calculated on the assumption that 1 oz. of gold has always the same value; only due to a loss, with time, of currency value it takes more money to buy the same 1 oz. of gold.

There are several colour-varieties of transparent, precious beryl. The most typical colours are the light blue, greenish-blue, or bluish-green of aquamarine, the yellowish-green of "aquamarine-chrysolite", and the yellow of yellow beryl, or golden beryl as the finest specimens are called. Rose-red and colourless beryl is less common, and is not, as a rule faceted. These varieties differ from the emerald in colour; they are also, as a rule, richer in faces, as shown in Fig. b to e, seldom showing forms other than the simple combination of a hexagonal prism and basal plane (Fig. a). In the following pages aquamarine will be fully dealt with and other varieties somewhat briefly, since they do not differ essentially from aquamarine in character or mode and place of occurrence.

Aquamarine is characterized by a pure sky-blue, bluish-green, or greenish-blue colour, very similar to the tint of sea-water; hence its name, and the old saying that this stone when placed in the sea becomes invisible. Aquamarine of a deep shade of colour is very rare; it is found, in small amount and of a fine deep, sapphire-blue, at Royalston in Massachusetts, U.S.A. A distinction is sometimes made between sky-blue beryl and beryl of a greenish-blue or bluish-green colour, the former being considered as aquamarine proper and the latter referred to as Siberian aquamarine. All pale bluish and greenish beryls are, as a rule, however, included in the term aquamarine.

The colours shown by precious beryl, and especially by aquamarine, are fine and brilliant, and their beauty is still more noticeable in artificial light. The colour in every case is supposed to be due not to chromium, as in the emerald, but to iron, which is always present to the extent of 1 to 2 per cent. Experiments have been made to test the stability of the colour of common greenish and yellow beryl from granite in the neighbourhood of Dublin. After an hour's exposure to a temperature of 357°C the crystals were observed to be still translucent, but to have lost the entire colour. When the crystals were fused a colourless, cloudy mass was obtained.

The dichroïsm of aquamarine of a sufficiently deep colour is appreciable; of the two images seen in the dichroscope, one is a pure but pale blue and the other very pale yellowish-green, almost colourless. The dichroïsm of specimens of a still deeper colour can be observed with the naked eye.

Aquamarine, and indeed precious beryl, is, as a rule, very uniformly coloured, irregularities in the distribution or character of the colouring being rare. Flawless and perfectly transparent stones are also very much less rare than are emeralds of the same description; fissures and turbid or cloudy patches are sometimes to be seen, however.

These latter are caused by the enclosure of numerous microscopically small cavities closely aggregated and either empty or containing a liquid. When these cloudy patches are present it is impossible to produce a good polish, although beryl, free from such faults, is susceptible of a very brilliant polish. In some crystals transparent and cloudy portions alternate, in which case the latter must be removed by cutting before the former can be utilised.

Precious beryl, including aquamarine, is, as a rule, cut in the brilliant form or in some modification of the step-cut. On account of the paleness of its colour the cut stone must have a certain depth or it will show too faint a colour. The lustre and colour of beryls is often improved by the use of foils; thus aquamarine is placed upon a silver foil or is mounted in a closed setting with a black lining. Very beautiful stones with not too pale a colour are mounted in all open setting. A magnificent faceted aquamarine, weighing 179 1/2 grams (875 1/2 carats), is to be seen in the mineral collection of the British Museum. Crystals of beryl often have the form of long and relatively thin prisms, and in correlation with this the girdle of the faceted stone has often an elongated outline. Large prisms of beryl are often cut in the East into dagger-handles and other articles of considerable size. In gems of such an elongated form the direction of greatest length coincides with the direction of the principal axis of the crystal, and the stone is set in such a position that its dichroïsm is most apparent. Aquamarine has been, and is, much used as a vehicle for the expression of the engraver's art; its comparative softness renders the work less arduous than is the case with many other precious stones. It is said that in ancient times beryl was the material of which the lenses for spectacles were constructed, and that from this originated the German word "Brille" (spectacles).

Transparent, finely coloured and flawless crystals of precious beryl, especially of aquamarine of considerable size, are by no means uncommon. Prisms of beryl of gem quality, and of the length and thickness of a man's thumb are frequently met with, and the discovery of still larger specimens is not unusual. In his work on precious stones, Barbot, the late Parisian jeweller, mentions a rough aquamarine of rare beauty of which the weight was about 10 kilograms (22 pounds), and for which 15,000 francs ($65,200) was asked. Again, a beautiful grass-green beryl, weighing 15 pounds, was found, in 1811, in Minas Novas, Brazil, and similar finds are often reported. It is not surprising, then, to find aquamarine and the precious beryls generally among the lowest priced gems, a carat stone of medium quality being obtainable for a few shillings. Only those stones, which are exceptionally beautiful in colour and perfect in every other respect, command higher prices, and even these fall far short of the value of a fair emerald. In this connection it may be mentioned that the value of beryl, unlike that of emerald, is proportional to the size of the stone.

Precious beryl, and especially aquamarine, is a mineral of somewhat wide distribution, occurring in gem-quality at many localities. Like the emerald it is met with, for the most part, in its primary situation in druses in coarse-grained granite and similar rocks. Its occurrence in secondary deposits, such as gem-gravels, is less usual, but not so rare as is the case with emerald.

Brazil is a country in which fine beryl is abundant. The stones are often cut before they are exported, but as the form they are given leaves much to be desired they are usually re-cut when they reach Europe. The mineral is found in great abundance, associated with chrysoberyl, white and blue topaz, etc., as pebbles in the sands of the Minas Novas district in the northeast corner of the State of Minas Geraes; also, though sparingly, associated with diamond in the diamond-sands of the same State. Among the pebbles of aquamarine are sometimes of considerable size; one weighing 15 pounds, which was found in the year 1811 near the source of the Rio São Matheus, in Minas Novas, has been already mentioned. Another fine pebble weighing 4 pounds was found soon after at the same place; but, as a rule, the pebbles are much smaller, their greatest diameter being no more than from 2 to 5 lines. The character of the rock in which the pebbles were originally formed is not certainly known; it is probably, however, a coarse-grained granite, since aquamarine is often found in a similar situation, and other precious stones found in Minas Novas are known to have been formed in a rock of this description.

In the neighbourhood of Rio de Janeiro aquamarine occurs in coarse-grained granite veins penetrating gneiss. At Vallongo in the year 1825 a fine crystal, weighing 4 pounds and valued at £600, was found. Previous to this had been found at the same place a transparent, faultless stone, which measured 7 inches in length and 9 lines in thickness. Beryl is abundant also in the Ural Mountains and elsewhere in Siberia. At many places crystals of gem-quality, associated, as in Brazil, with topaz, are to be found, so that the importance of Siberia as a locality for beryl is comparable to that of Brazil.

In the Urals it is found at various places in the neighbourhood of Ekaterinburg in the Government of Penn, also on the Ilmen Lake near the Ilmen Mountains, as well as in gold-washings on the Sanarka River in the Southern Urals, the two latter localities being in the Government of Orenburg.

In the Ekaterinburg district it is found principally in the neighbourhood of the villages of Mursinka (Mursinsk) and Shaitanka (Shaitansk), occurring in drusy cavities in coarse-grained granite, which is penetrated by veins of fine-grained granite.

The finest beryl to be found in the Urals occurs in the neighbourhood of Mursinka. It is usually in transparent, well-developed hexagonal prisms, which may be wine-yellow, greenish-yellow, yellowish-green, bluish-green, or pale blue in colour, and which range in length from a few millimetres to three decimetres (1 foot). The crystals are, as a rule, single, but intergrowths are occasionally met with in which the crystals are arranged irregularly or in parallel position. A group of fine yellowish-green or asparagus-green crystals, perfectly transparent and grown together in parallel position, was found in 1828. The group, which measures 27 centimetres in length and 31.2 centimetres in circumference, was in the collection of the Imperial

Institute of Mines at St. Petersburg, and has been valued at 43,000 roubles ($739,800). The cavities in the rock, to the walls of which the crystals are attached, are usually filled with brown clay, and the presence of this substance is considered to indicate that beryl is to be found not far away. Associated with the beryl are quartz, felspar, mica, and black tourmaline, also topaz and amethyst.

There are numerous pits or mines from which these variously coloured stones are won. For the most part the stones were worked in the gem-cutting establishments of Ekaterinburg. Formerly all the mines clustered round the village of Mursinka, but later other mines were opened in the neighbourhood of the villages of Alabashka, Sisikova, Yushakova, Sarapulskaya, and others, the population of which consists almost exclusively of gem-seekers. The beryls of Shaitanka were known as far back as the year 1815; they are colourless or of a pale rose shade, and therefore less importance as gem-stones.

Aquamarine deposits in Ural Mts.

FIG. Occurrence of beryl near Mursinka, Urals.

Magnificent specimens from this and other localities are to be seen and admired in all mineral collections. The position of the mines in the neighbourhood of Mursinka is shown in the accompanying map. The pale apple-green beryls, which accompany the emerald at Takovaya are of less value. Those found on the Ilmen Lake also are only in part of gem-quality. They occur on the eastern shores of this lake, four miles northeast of the smelting works of Miask in the Ilmen Mountains, and to the south of Ekaterinburg, in the Zlatoust Mining district, latitude about 55° N. Crystals of beryl from this locality sometimes reach a length of 25 centimetres; they are bluish-green inclining to leek-green in colour, much fissured, and, as a rule, only translucent. They occur, together with topaz crystals, also fissured, and green felspar (amazon-stone), in pegmatite veins penetrating the rock known as miascite.

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Diamond Diamond Geology and Mining Diamond Trade

Rafal Swiecki, geological engineer email contact
February, 2006

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