“The Opal, when pure and uncut in its native rock,” says Ruskin in his
lecture on Color, “presents the most lovely colors that can be seen in
the world except those of clouds.”
While not all of us may share the great art critic’s preference for
uncut stones, there are few probably who will not join him heartily in
his admiration of the brilliant gem from whose depths come welling up
tints of so varied hue that we appropriately speak of them as colors at
play. Our interest in these colors may be heightened by reading what
Ruskin has further to say of them: “We have thus in nature, chiefly
obtained by crystalline conditions, a series of groups of entirely
delicious hues; and it is one of the best signs that the bodily system
is in a healthy state when we can see these clearly in their most
delicate tints and enjoy them fully and simply with the kind of
enjoyment that children have in eating sweet things. I shall place a
piece of rock opal on the table in your working room; and if on fine
days you will sometimes dip it in water, take it into sunshine and
examine it with a lens of moderate power, you may always test your
progress in sensibility to color by the degree of pleasure it gives
you.”
The Opal is indeed one of the most fascinating of gems; yet often
elusive and at times disappointing. Of its freaks and foibles strange
stories are told. Gems of brilliant quality are known suddenly to have
lost their hues never to regain them, while others previously dull and
lusterless have become radiant as the rainbow.
Prof. Egleston, of New York city, relates that a bottle of cut Opals
once given him by a prominent jewelry firm because they had lost their
color, after remaining in his cabinet for a time regained their
brilliancy and retained it. But to have opals regain their color is,
unfortunately, far less usual than for them to lose it. The gem often
exhibits brilliant colors when wet either with water or oil that
disappear when it is dry. Taking advantage of this peculiarity dishonest
dealers often keep opals immersed until just before offering them for
sale. The experience of having stones so treated as well as others which
might with more reason be expected to retain their brilliancy, lose it,
has very likely led to the superstition commonly attached to the Opal
that it is an unlucky gem. Some authorities, however, trace the origin
of the superstition to Sir Walter Scott’s novel, “Anne of Geierstein,”
in which the baleful influence of the Opal plays a prominent part, and
it is stated that within a year of the publication of the book the price
of Opals declined fifty per cent in the European market. Even if the
superstition did not originate in either of these ways it was probably
from a source quite as trivial and it should prevent no one from
enjoying the pleasure to be derived from the beauties of this gem.
Chemically, Opal is oxide of silicon with varying amounts of water, the
water varying from 3 to 9 per cent. It is, therefore, closely allied to
quartz, but differs physically in being softer and not as heavy.
Further, it never crystallizes, and it is soluble in caustic potash,
which quartz is not. It is infusible, but cracks and becomes opaque
before the blowpipe. In sulphuric acid it turns black, on account
probably of the organic matter it contains.
Its hardness is sometimes as low as 5.5 in the scale in which quartz is
7 and its specific gravity is from 1.9 to 2.3, while that of quartz is
2.6. On account of its relative softness a cut Opal often does not
retain its polish well and requires frequent smoothing. Opals when first
taken from the ground are often softer even than the above and for this
reason it is usual and desirable to allow them to harden or “season,” as
it is called, for some time after quarrying, before they are polished.
[Illustration: OPAL.
LOANED BY FOOTE MINERAL CO.]
Top row:
Precious Opal in Matrix (Queensland.)
Wood Opal (Idaho.)
Precious Opal (New South Wales.)
Center:
Precious Opal (New South Wales.)
Precious Opal (New South Wales.)
Fire Opal in Matrix (Mexico.)
Bottom:
Prase Opal (Germany.)
Opal as a mineral is quite common, so that no one need suppose because
he has specimens labeled “opal” in his collection that he has as many
precious stones. It occurs in many varieties, and, especially if it
contains foreign matter, in many colors. Nearly all silica deposited by
hot waters is in the form of Opal, so that the geysers of Yellowstone
Park build up cones of Opal and fall into Opal basins. This particular
form of Opal is known as geyserite, and it is often differently colored
by different ingredients.
Wood is often preserved by silica in the form of Opal, the siliceous
waters taking away the wood and replacing it by Opal, grain by grain,
with such delicacy and accuracy that the structure of the wood is
perfectly maintained. The minute shells which diatoms make consist of
Opal, and when these dead shells accumulate to form deposits of some
extent we call the powdery substance tripoli and use it for polishing
silverware and other metals. Then there are hyalite, a variety of Opal
looking like transfixed water, so clear and colorless is it; hydrophane,
a translucent variety which sticks to the tongue and becomes more nearly
transparent when soaked in water; cacholong, a porcelain-like variety,
and menilite, a concretionary variety.
Common Opal varies from transparent to opaque, being most often
translucent and sometimes exhibiting the peculiar milkiness of color
which we call opalescence. It has sometimes a glassy, but often a waxy
luster, the latter when pronounced giving rise to the varieties known as
wax Opal and resin Opal. When Opal has the banded structure of agate it
is known as Opal-agate; when it has the color of jasper as jasper Opal,
and when that of chrysoprase as prase Opal. But none of these varieties
are used in any quantity as gems. This distinction is reserved almost
wholly for the variety known as noble or precious Opal. This is Opal
which exhibits a play of colors. No essential chemical or physical
distinction between noble Opal and other varieties is known. In a large
vein of Opal portions will exhibit the play of colors and the remainder
will not, but why the difference has not yet been determined. Neither
can the origin of the varied coloring; i. e., the iridescence, be
determined. Some regard it as due to interspersed layers containing
different percentages of water, which break up the rays of light
somewhat as a prism does, while others think that minute cracks and
fissures through the stone furnish surfaces from which the rays are
reflected in different colors back to the eye. Some Opals which are dull
and lusterless when dry exhibit considerable play of color when immersed
in water, and this fact seems to favor the first theory of the cause of
the iridescence, but the subject is not understood. The character of the
play of colors differs in different Opals, and this gives rise to
different varieties. The true noble Opal has the color quite uniformly
distributed. When the color appears in flashes of red, yellow, etc., the
stone is known as fire Opal; if blue as girasol, and if chiefly yellow
as golden Opal. When the patches of color are small, angular and
uniformly distributed it is called harlequin Opal, and if these are long
and somewhat parallel, flame Opal. These colors are not, of course,
inherent in the stone, its color varying from colorless to opaque white.
The black Opals sometimes seen and highly prized by some are usually
artificial, and are made by soaking ordinary Opals in oil and then
burning oil on them. The brilliancy of the stone is thus increased, but
it is usually fragile and liable to lose color.
Any Opal will lose its play of colors on being heated too highly, hence
possessors should avoid subjecting them to more than ordinary heat. It
is the variety and brilliancy of their changing colors which give to
Opal nearly all its desirability as a precious stone, for, as has often
been remarked, the qualities of hardness, transparency and rich body
color which give to most other gems their value are lacking in the Opal.
But together with the beauty of its changing colors Opal possesses an
advantage over all other gems in that it cannot be successfully
imitated. It is said that the Romans were able to make artificial Opals
closely resembling the real, but, if so, the art has been lost never to
be recovered, and we may hope it never will be. Hence, however much
danger there may be in buying an Opal that it has not been properly
“seasoned,” or may not retain its color, the purchaser may at least be
sure he has an Opal and not an imitation. The stones are usually cut in
the oval form known as en cabouchon, this cutting being found to bring
out their brilliancy better than any facetted form. The brilliancy of
the stone may be increased in setting by giving it a backing of mother
of pearl or black silk. When a number of Opals are placed together they
seem to borrow brilliancy from one another, a fact which is taken
advantage of in settings by placing a number together and also by Opal
dealers to dispose of inferior stones by grouping them with good ones.
For this reason when Opals are purchased they should be examined
separately. The value of Opals depends almost wholly on the brilliancy
of their coloring and their size. Stones without the play of colors are
practically worthless, while stones of ten to twenty carats’ weight,
with brilliant coloring, may bring several hundred dollars. The most
highly valued Opals have long come from the mines of Czernowitza in
northern Hungary. These Opals are often known as Oriental Opals from the
fact that in early days they were first purchased by Greek and Turkish
merchants, and by them sent to Holland. There are, however, no
localities in the Orient where precious Opals are found. The rock in
which the Hungarian Opals occur is eruptive, and of the kind known as
andesite. It is considerably decomposed, and the Opal occurs in clefts
and veins. There is little doubt that it was from these mines that the
Romans obtained the Opals known to them, and the output has been quite
constant since.
It is said that the Hungarian Opals are less likely to deteriorate than
any others. Still the danger of deterioration is not great in any Opal.
The other important countries from which precious Opals are obtained are
Mexico, Honduras and Australia. The Mexican Opals are mostly of the fire
Opal variety. They are mined in a number of the States of the
Republic—Queretaro, Hidalgo, Guerrero, Michoacan, Jalisco and San Luis
Potosi. The oldest mines are in the State of Hidalgo, near Zimapan,
where the Opal occurs in a red trachyte. Most of the Mexican Opals on
the market at the present time, however, come from the State of
Queretaro, where mining for them is conducted on a more extensive scale.
The Opal here occurs in long veins in a porphyritic trachyte, and is
mined at various points. The stones are cut and polished by workmen in
the city of Queretaro who use ordinary grind-stones and chamois skins
for the work and are said to receive an average wage of 23 cents a day.
The Honduras Opals reach foreign markets but rarely and usually uncut.
The mines are in the western part of Honduras, in the Department of
Gracias. They are little worked, but there is no doubt that extensive
deposits exist which might afford a good supply of gems if they were
properly exploited. The Australian Opals come from several localities,
the most prominent at the present time being White Cliffs, New South
Wales. The matrix is a Cretaceous sandstone which has been permeated by
hot volcanic waters. Shells, bones and other fossils are found here
entirely altered to precious Opal, making objects of great beauty. In
1899 Opals to the value of $650,000 were sold from this single region.
There is no doubt that the present popularity of the Opal is due to some
extent to the supply of beautiful stones which has come from these mines
at prices at from one-third to one-tenth those of the Hungarian stones.
Other localities in Australia whence precious Opals are obtained are
places on the Barcoo River and Bulla Creek, Queensland, and occasional
finds in West Australia.
No localities in the United States yielding precious Opals in any
quantity have yet been discovered. Some good stones have been cut from
an occurrence in Idaho, and some other minor finds have been made, but
they possess little commercial importance at present.
Opal does not seem to have been extensively known or used by the
ancients, although we know the Romans prized it highly and ascribed to
it the power of warning against disaster. The Roman Senator Nonius owned
one set in a ring which was said to be valued at nearly a million
dollars. History records that for refusing to sell the stone to Mark
Antony he was sent into exile. The next most famous Opal in history is
one owned by the Empress Josephine which was called “The Burning of
Troy,” on account of the brilliancy of the flames which shot forth from
its depths. The present whereabouts of neither of these gems is known. A
large Mexican Opal, now in the Field Columbian Museum, is carved in the
image of the Mexican sun-god, and has a setting of gold representing the
diverging rays of the sun. This gem is very ancient and is believed to
have been kept by the Aztecs in a temple, so it is probable that the
Aztecs knew and prized Opals.
The Arabians believe that Opals fall from heaven with the lightning’s
flash, a beautiful fancy, indeed. Modern usage makes the Opal the
birthstone of the month of October, some of the properties assigned to
it being that it has the power of making its wearer a general favorite,
enhancing the keenness of his sight and shielding him from suicide.
October’s child is born for woe
And life’s vicissitudes must know;
But lay an Opal on her breast
And Hope will lull those woes to rest.
Oliver Cummings Farrington.