About the Properties and Historical Value of Opals

The precious opal is one of the most individual of gems; of all the opaque minerals, it reveals the most beautiful play of colours, in folklore it is the birth-stone of October and the symbol of hope, and yet, for years, the fame of this fire-flashing stone was blackened by a cloud of superstition which condemned it as unlucky; a superstition the origin of which is obscure. For a time, however, it largely regained its lost popularity, having found its most illustrious patron in Her Majesty, the late Queen Victoria. Another remarkable fact about the opal is that it is not found in the Orient--the very land of gems.

Opal, in mineralogy, is Hyalus opalinus, of the order Hyalina; it is of granular structure; small reniform and stalactitic shapes and large tuberose-like concretions; hardness 5.5 to 6.5; specific gravity 2 to 2.21; lustre vitreous, sometimes inclining to resinous or pearly; streak, white; colour, white, yellow, red, brown, green, or gray. The colour is usually pale, due to foreign elements. Some opals exhibit a rich play of colours, while others present different colours by refracted and reflected light. The cause of the colour-play is the physical condition resulting from a multitude of fissures having striated sides which diffract and decompose the light. The chemical composition of the opal is ninety per cent. silica and ten per cent. water.

Besides precious opal, there is the harlequin opal which presents a variegated play of colours on a reddish ground, and resembles the fire opal which shows hyacinth red to honey-yellow colours, with fire-like reflections. Girasol is bluish-white and translucent, and, under a strong light, presents reddish reflections. Lechosos opal is a variety remarkable for flashes of green. Hydrophane, a light coloured opaque kind, becomes transparent when immersed in water. Cacholong is an opaque porcelain, bluish, yellowish, or reddish white. Opal agate has an agate-like structure. Jasp opal contains iron, and is to opal as jasper is to quartz. Wood opal is wood silicified by opal. Hyalite (Muller's glass) is colourless and clear, or translucent and a bluish white. Moss opal contains manganese oxide, and is to opal as moss agate is to quartz. A freakish variety of opal is tabasheer, a silica deposited within the joints of bamboo; it is absorbent, and, like hydrophane, becomes transparent when immersed in water.

As a mineral, opal is quite common, so that an amateur's collection of minerals can include specimens to represent opal--some of them very beautiful, too--at small cost, or for the effort of prospecting, in many localities. The varieties of opal are many, and the frequent inclusion of foreign matter invests it with a wonderful variety of colours. The silica deposited by nearly all natural hot waters is opalescent. The Yellowstone Park geysers shoot up around cones of opal raised by the constant accretions of silica deposited by the passing hot waters, which fall into opal basins created in the same way. This variety of opal is termed geyserite. There is a wide gulf in values between precious or noble opal--the gem stone quality--and opal in general.

Opal is generally found filling seams, cavities, and fissures in igneous rocks, also embedded in limestone and argillaceous beds.

Opals of a quality fit for use as ornamental stones are found in many lands. Mines in Czernowitza, in northern Hungary, long produced the most highly valued gem opals obtainable. These opals are often known as "Oriental opals," because they first appeared in Holland through Greek and Turkish traders. Despite the trade practice of applying the term "Oriental" to this type of opals, none is found in the Orient. The Hungarian opals were undoubtedly those first known to the Romans. The claim is made that Hungarian opals are less likely to deteriorate than any other variety. Gem opals are also found in Australia, Mexico, and Honduras. Although opals are produced to a commercial extent in several Mexican states, they are most systematically mined in Queretaro, where the opal occurs in long veins in a porphyritic trachyte. This opal mining has created a somewhat primitive cutting and polishing industry in the city of Queretaro. The exporting of Honduras opals--all uncut--is not extensive. In the United States the occurrence of gem opal has been observed in the John Davies River, Oregon, and near Whelan, between the Coeur d'Alene and Nez Perces Indian reservations, almost on the Idaho line, State of Washington. The most prolific source of opals in recent years has been the Australia mines, the most prominent being White Cliffs, New South Wales. Extensive mining operations are carried on there, the matrix of the opal being a cretaceous sandstone, which has been permeated by hot volcanic waters. The output of this region has already been represented by millions of dollars. Opals have been obtained in commercial quantities at localities on the Barcoo River and Bulla Creek, Queensland, and are occasionally found in West Australia.

The admiration of the ancients for the opal is expressed by Onomacritus, writing five hundred years B.C., who remarks: "The delicate colour and tenderness of the opal remind me of a loving and beautiful child." Pliny, whose voluminous books covered so wide a range, and who evidently believed himself qualified to write about anything, wrote of the opal: "It is made up of the glories of the most precious gems, and to describe it is a matter of inexpressible difficulty." The ancients esteemed the opal highly, and attributed to it an influence for every possible good; this belief outlasted the Middle Ages, and in the early part of the seventeenth century the opal is recorded as being as highly valued as ever. Then arose a superstition that the fiery stone was unlucky, and this became prevalent everywhere. The cause of this has been attributed to Walter Scott's novel Anne of Geierstein. A genuine reason why opal may have come to be regarded as unlucky by its possessors is its mutability. The changes which may occur in the opal are not only numerous but freakish and uncanny. Brilliant opals have lost their fires and lustre forever, while others have lost and recovered them. In other cases dull specimens have suddenly developed brilliancy. Mediocre specimens will sometimes, when moistened with oil or water, exhibit a fine colour play, which will vanish when the stones dry, and this peculiarity has been utilised for profit by dishonest dealers. A stone thus acquired would be unlucky for the purchaser.

Credit for the reinstatement of the opal in public favour is believed by the author to be due in great part to the late Queen Victoria, who, in many ways, demonstrated her royal favour for the stone of many fires and colours, and there is no doubt that the Queen's motive was to benefit her colonial subjects in Australia, where opals had been discovered.

Queen Victoria gave to each of her daughters, at their marriage, opals, and this and other acts which signified her admiration for the stone and her disdain for the superstition through which its reputation had fallen into evil days soon raised opals high in the realm of precious stones; the result being that Australian exports of opal were handsomely increased by the demand for, and shipment of, the stone thus royally reinstated to its ancient high estate of popular favour.