Opal​—A Rainbow in Your Hand

By “Awake!” correspondent in Honduras

KNOTTING my rope around the base of a firm pine, I flung its loose end into a muddy hole and slid down 20 feet (6 meters) to the bottom. There tunnels barely head high fanned out horizontally in all directions, like the spokes of a bicycle wheel. Choosing one, I followed it for about 30 feet (9 meters), scanning the walls continually with the aid of a hissing lamp.

In very few of the picturesque mountains of Honduras can such diggings be found. They were dug some 400 years ago by Spaniards in search of the gemstone opal. In this locality, the Spaniards found small clusters of opal pebbles and some larger nodules of the rare gem. But they did not find the best, located higher up the mountain in fissures cut vertically through a massive outcrop of tough black basalt.

Opals constitute some of the world’s most beautiful gems; and they are unusual in composition. Notes The World Book Encyclopedia: “Gemmologists speak of an opal as a hydrated silica gel, because it contains water along with the silica.” The substance silica makes up about 60 percent of earth’s crust. Where hot silica-rich solutions have seeped into cracks and cavities underground, the jelly may solidify into opal.

Not all opal is valuable. “Common” opal, for example, usually is not a precious stone and does not reflect a variety of colors. Australian miners scornfully call it “potch.” Only in about seven or eight countries of the world has “precious” opal been discovered. At present a reputed 95 percent of the world’s opal comes from Australia, though recent South American discoveries may change the scene.

Finding precious opal is worth the effort. Bringing such a gem near to a light source causes a whole rainbow of colors to leap out from the stone. Slowly rotating an opal or switching it from sunlight to artificial illumination results in color upon color shooting forth in a flood of beauty.

What causes opal to spray forth so many colors? This is not exactly known. A theory that has gained wide acceptance today attributes the bending of light rays by opal to sheets of microscopic silica spheres of which the gem is composed.

Persons desirous of purchasing uncut opal have need of caution. Certain classes of opal are unsuitable for making gemstones. Some have a very porous and chalky aspect. Others will lose their color entirely within a month. And it is common for certain opals to shatter in a dry atmosphere, due to evaporation of water from the gel.

Are you thinking of buying an opal? Before doing so it would be wise to consider some basic facts. For one thing, opal is infinitely variable; no two stones are exactly alike. Among the many classes of this gemstone are black opal, boulder opal, seam opal, fire opal and flame opal. Other names describe the various color patterns that opal can present. For example, “pin fire” features numerous pinpoints of color, as if on a starry night. The “Harlequin pattern” is a mosaic of larger colored squares.

Gem cutters usually prepare opal as a “cabochon,” that is, a stone with a rounded, convex top. The shape of the stone as a whole may be round, oval, rectangular or “freeform.” This latter style enables the cutter to avoid grinding off scarce and precious material simply to conform to an arbitrary shape. And freeform adds to a stone’s individuality.

Cutters of gemstones prepare opal in three basic ways: solid, doublet and triplet, as illustrated above.

Though all of these are genuine opal, the solid stone generally will cost more than the doublet or triplet. For everyday use, one may find it best to buy a quartz-capped triplet, since quartz is more scratch resistant than opal. Looking at the stone from its side will reveal whether it is solid or otherwise.

Famous opals throughout the world are few and far between. The giant of them all is the “Olympic Australis,” 20,000 carats of uncut scintillating fire, the size of a man’s head.

What are the possibilities of unearthing your own opal? Judging by my own experience, they do not appear promising. After five painful hours astride a mule fully aware of its rider’s incompetence, I found exactly nothing. True, the misty mountains still conceal many a glittering opal. But they are locked in tough basalt overlaid with stately pines or steaming jungle. Yet, do not let me discourage you. Discover one if you can!

[Diagram on page 25]

(For fully formatted text, see publication)

Solid

Doublet

Opal

Potch or other material

Triplet

Quartz cap

wafer of Opal

Potch or other material