BERYL
(_Emerald_, _Aquamarine_, _Morganite_)
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 to-day
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 aquamarine 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, Be_{3}Al_{2}(SiO_{3})_{6}. The beryllia is often partially
replaced by small amounts of the alkaline earths, caesia, potash, soda,
and lithia, varying from about 1½ 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.
[Illustration: FIG. 70.—Emerald Crystal.]
The name of the species is derived from the Greek βήρυλλος, 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 understood
by the name. Emerald is derived from a Persian word which appeared
in Greek as σμάραγδος, 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 1·590,
and 1·572 and 1·598 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 7½ 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 1529 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 devoted 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-north-west 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 276·79 grams (9¾ 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 (156½ carats), and
measures 1⅛ 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, on Plate I, Fig. 5.
[Illustration: FIG. 71.—Duke of Devonshire’s Emerald.
(Natural 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 £15 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 £1600 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. On 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
aquamarines 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 (14½ km.) north-east 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. (110·5 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).
[Illustration: _PLATE XXVI_
LARGE AQUAMARINE CRYSTAL (_one-sixth natural size_), FOUND AT
MARAMBAYA, MINAS GERAES, BRAZIL]
PART II—SECTION B
SEMI-PRECIOUS STONES