This mineral species includes a number of varieties which are highly
valued as gems. These are, besides Beryl itself, the gems emerald,
aquamarine and golden beryl. Chrysoberyl, it may be noted, is not a
variety of Beryl, but a distinct species.
While these gems all differ in color, they are the same mineral and are
practically identical in composition, hardness and other properties. In
composition they are a silicate of aluminum and glucinum, the percentage
being, for normal beryl, 67 per cent of silica, 19 per cent of alumina
and 14 per cent of glucina.
The beautiful green color of the emerald is probably due to a small
quantity of chromium which it usually contains, though some authorities
believe organic matter to be the coloring ingredient. To what substance
the other varieties of the species owe their color is not known.
In hardness the varieties of Beryl differ little from quartz, the
hardness being 7.5 to 8 in the scale of which quartz is 7. They are
somewhat inferior therefore to such gems as topaz, sapphire and ruby in
wearing qualities, although hard enough for ordinary purposes.
The specific gravity of Beryl is also about like that of quartz, ranging
from 2.63 to 2.80; the specific gravity of quartz being 2.65. The
varieties of Beryl are therefore relatively light as compared with other
gems.
Beryl crystallizes in the hexagonal system. It usually occurs as
six-sided prisms, commonly terminated by a single flat plane, but
sometimes by numerous small planes giving a rounded effect and
occasionally by pyramidal planes which cause the prism to taper to a
sharp point.
The crystals sometimes grow to enormous size, exceeding those of any
other known mineral. Thus, one found in Grafton, New Hampshire, was four
and one-quarter feet in length and weighed two thousand nine hundred
pounds. Another in the same locality is estimated to weigh two and
one-half tons. In the museum of the Boston Society of Natural History
and in the United States National Museum are exhibited single crystals
also of great size. That in Boston is three and one-half feet long by
three feet wide and weighs several tons. That in the National Museum
weighs over six hundred pounds.
None of these crystals are of a high degree of purity or transparency,
but the crystal planes at least of the prisms are well developed.
Beryl crystals have no marked cleavage except a slight one parallel with
the base. Where broken, the surface shows what is called conchoidal
fracture, i. e. it exhibits little rounded concavities and convexities
resembling a shell in shape.
The mineral is quite brittle. Some emeralds even have the annoying habit
of breaking of their own accord soon after removal from the mine. This
can be prevented by warming them gradually before exposing them to the
heat of the sun or other sudden heat.
Beryl and its varieties, like tourmaline, are dichroic, i. e. the stones
exhibit different colors when viewed in different directions. This
dichroism can sometimes be observed by the naked eye, but often not
without the aid of the instrument known as the dichroscope. When seen it
furnishes a positive means of distinguishing a true stone from any glass
imitations.
The varieties of Beryl have none of the brilliancy of the diamond and
therefore depend wholly on their body colors and their lustre for their
beauty and attractiveness. Fortunately they exhibit these qualities as
well by artificial light as by daylight.
[Illustration: BERYL.]
First row:
Golden Beryl (Siberia).
Blue Beryl (Albany, Maine).
Aquamarine (Ural Mountains).
Second row:
Aquamarine (Conn.)
Third row:
Blue Beryl (Siberia).
Golden Beryl (Conn.)
Emerald in the Matrix (Ural Mountains).
Ordinary Beryl is a mineral of comparatively common occurrence, being
often found in granitic and metamorphic rocks.
That of common occurrence is usually too clouded and fractured to be of
use for gem cutting. There are many localities, however, where Beryls of
gem quality occur.
The finest emeralds in the world come from Muso, a locality in the
United States of Colombia, seventy-five miles N. N. W. of Bogota. It is
a wild and inaccessible region and the mining of the gems is a
precarious occupation. The emeralds occur according to Bauer in a dark,
bituminous limestone which is shown by fossils to be of Cretaceous age.
As emeralds in other localities occur only in eruptive or metamorphic
rocks, it seems probable that the Muso emeralds have washed in from an
older formation. The emerald bearing beds are horizontal, overlying red
sandstone and clay slate. Calcite, quartz, pyrite and the rare mineral
parisite are other minerals found associated with the emerald. The
manner of working these emerald mines is thus described by Streeter:
“The mine is now worked by a company, who pay an annual rent for it to
the government, and employ one hundred and twenty workmen. It has the
form of a tunnel of about one hundred yards deep, with very inclined
walls. On the summit of the mountains, and quite near to the mouth of
the mine, are large lakes, whose waters are shut off by means of
water-gates, which can be easily shifted when the laborers require
water. When the waters are freed they rush with great rapidity down the
walls of the mine, and on reaching the bottom of it they are conducted
by means of an underground canal through the mountain into a basin. To
obtain the emeralds the workmen begin by cutting steps on the inclined
walls of the mine, in order to make firm resting places for their feet.
The overseer places the men at certain distances from each other to cut
out wide steps with the help of pickaxes. The loosened stones fall by
their own weight to the bottom of the mine. When this begins to fill, a
sign is given to let the waters loose, which rush down with great
vehemence, carrying the fragments of rock with them through the mountain
into the basin. This operation is repeated until the horizontal beds are
exposed in which the emeralds are found.”
The next most prominent locality whence gem emeralds are obtained is
that in Siberia on the river Tokovoya, forty-five miles east of
Ekaterinburg. The emeralds here found are often larger than any yet
obtained in South America, but they are not of so good quality. They
occur in mica schist (see colored plate), and often associated with the
mineral phenacite, chrysoberyl, rutile, etc.
Other localities whence emeralds are obtained are Upper Egypt (the
source of those known to the ancients), the Heubachthal in Austria, and
Alexander county, North Carolina, in our own country. The latter
locality is no longer worked, but it has afforded a number of fine
crystals.
Aquamarines and transparent Beryls are found in Siberia, India, Brazil,
and in many localities in the United States. Dana describes an
aquamarine from Brazil which approaches in size, and also in form, the
head of a calf. It weighs two hundred and twenty-five ounces troy, is
transparent and without a flaw. In the Field Columbian Museum is to be
seen a beautiful cut aquamarine from Siberia more than two inches in
diameter and weighing three hundred and thirty-one carats. Here is also
the finest specimen of blue Beryl ever cut in the United States. It was
found in Stoneham, Me., is rich sea green color in one direction and sea
blue in another. It weighs one hundred and thirty-three carats. Numerous
other Maine localities have furnished gem Beryls. Golden Beryls are
found in Maine, Connecticut, North Carolina, Pennsylvania and other
United States localities, as well as in Siberia and Ceylon. From them
are obtained gems of rich golden color resembling topaz.
Beryl of a pale rose color is sometimes found, and when of good quality
is cut for gem purposes, but it is of too rare occurrence to be
important.
Emeralds seem to have been known and prized from the earliest times.
They are mentioned in the Bible in several places, the earliest mention
being in Exodus, where they are described as one of the stones making up
the ephod of the high priest.
Their use in Egypt dates back to an unrecorded past and they frequently
appear in the ornaments found upon mummies. Readers of Roman history
will remember that the Emperor Nero used an emerald constantly as an eye
glass.
The Incas, Aztecs and other highly civilized peoples of South America
were found using these gems profusely for purposes of adornment and for
votive offerings when first visited by the Spaniards. It was partly the
desire to secure these gems which led Cortez and his followers, early in
the sixteenth century, to undertake the conquest of Peru. Some of the
emeralds wrested from the Incas by Cortez and brought to Spain are said
to have been marvels of the lapidary’s art. One was carved into the form
of a rose, another that of a fish with golden eyes, and another that of
a bell with a pearl for a clapper.
During the years following Cortez’ conquest large quantities of emeralds
were brought to Europe, and they became much more popular and widely
distributed than previously. Joseph D’Acosta, a traveler of the period,
says the ship in which he returned from America to Spain carried two
chests, each of which contained one hundred pounds’ weight of fine
emeralds.
From what locality the Peruvians themselves obtained these gems is not
known, unless it was the Colombian locality at Muso, already described.
The Spaniards were led to these mines in 1558. They continued the
working of them, and there has been practically no interruption in their
operation since that time.
The ancients had many superstitions regarding the emerald, one being
that it had a power to cure diseases of the eye. Another was that it
would reveal the inconstancy of lovers by changing color.
“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 faithless, like those leaves when withering.”
So writes one poet.
Again, they believed the emerald would blind the eyes of the serpent:
“Blinded like serpents when they gaze
Upon the emerald’s virgin blaze.”
—Moore.
Of these traditions, perhaps the only one held in any esteem at the
present time is that which associates the emerald with the month of
June, making it the talismanic gem or “birth stone” of persons born in
that month.
The largest and most beautiful emerald known to be in existence at the
present time is one owned by the Duke of Devonshire. This is an uncut
six-sided crystal about two inches long and of the same diameter. It is
of perfect color, almost flawless and quite transparent.
Like all other gems, the value of emeralds varies much according to
their perfection. Those of the best grade are worth at least one hundred
dollars a carat. The color should be a dark velvety green, those of
lighter shades being much less valuable. Owing to the extreme
brittleness of the mineral, emeralds usually contain flaws, so that “an
emerald without a flaw” has passed into a proverb to indicate a thing
almost unattainable.
Aquamarine and other varieties of Beryl seem not to have been as highly
esteemed as emerald by the ancients, although Beryl is mentioned in the
Bible, and early writers describe gems evidently belonging to the
species. They were probably less well known to the ancients, as nearly
all the localities from which aquamarines and Beryls are now obtained
are of comparatively modern discovery. They are gems in every way as
worthy as the emerald, however, and will doubtless become more popular
as their qualities are better known.
Oliver Cummings Farrington.