Opal: Australia's Gemstone Trivia Quiz

Answer: Slovakia

In antiquity, opals were extremely rare as neither Australia nor the Americas, the primary and secondary sources of opal in modernity, were part of the "known" world; therefore, opal was highly prized by European royalty. Long before the expansive deposits in Australia were located, the main European source was Červenica, in present-day Slovakia.

Answer: Lightning Ridge

Lightning Ridge, NSW not only provides the greatest quantity of black opal in Australia, it produces the best quality. Although the finest black opals come from Lightning Ridge, Australia, the Virgin Valley, Nevada, USA, also has produced some comparable specimens.

Kotroit, Queensland, is a source of boulder opal. Melbourne is the capital of Victoria. Coolgardie is for gold, not opal, and has been called "the mother of Western Australia Goldfields".

Answer: water & silica

Water and silica are not only the main components of opal but also the main components of glass. Opal is about 10% water, specifically rainwater. As rainwater passes through the ground, it picks up silicon deposits. Then it seeps down into rocky crevices.

After most of the water evaporates, the deposited silica and what's left of the rainwater combine to form opal--but not quickly. In about 5 million years, just one centimeter of opal will solidify, making opal an ancient gem indeed. In fact, about 20 million years ago, Australia was flooded with silica-rich rainwater, which is why it is the primary source of opal today.

Answer: Precious may have play of color

Opal may be transparent, translucent, or opaque, depending on the precise conditions under which it was formed, but its opacity does not define whether it is precious or common. As you turn a precious opal in white light, the colors appear to change. Or likewise if you walk around an opal, you will also see colors change, as millions of tiny, tiny spheres in the silica adhere to each other, and the spaces between them diffract light.

This phenomenon, which causes various shapes and sizes of spectral colors, is known by gemologists as play of color. Common opal has a hazy-milky-turbid sheen, which gemologists call opalescence, with no play of color (iridescence).

Answer: black

Whereas white, gray, and green opals are the most common colors of opal, the black opal (which is actually dark gray to blue-black displaying the play of color) is the rarest of the rare. Of course by this is meant the precious black opal; there is a black common opal, or potch, which is sometimes used to back precious black opal in what is called an opal doublet. Backing a black opal with a dark material such as potch, onyx, or obsidian will emphasize the play of color and produce a lovelier setting than a white or light-colored backing.

Boulder opal is perhaps the second most valuable opal, being a mixture of ironstone and black opal. Its popularity has grown since the 1970s.

Answer: precious

Some precious opals, like fire opal, do not have play of color (iridescence) but do have a vibrant color display, unlike the common opal which does not. Fire opal does have the varying spectral colors, but it does show occasional flashes of bright green. A well-known deposit of fire opals is in the state of Querétaro, Mexico. Some people call fire opals "jelly opals".

Answer: Coober Pedy

The Olympic Australis, the largest and most valuable opal in the world, was discovered in Coober Pedy, South Australia, in 1956. Miners found it at the Eight Mile opal field some 30 feet (9.1m) below the earth. The enormous gem was named after the Olympics, which in 1956 were held in Melbourne. The ponderous stone has been left unpolished in its natural state., blemishes and all. It measures 11 inches (280mm) long, 4¾ inches (120mm) thick, and 4½ inches (115mm) wide and weighs 17,000 carats (that's 7.6 pounds or 3.45 kg).

Andamooka is another mining town of South Australia and produces matrix opal, crystal opal, and black opal, but Quilpie and Jundah are in Queensland and are the main sources of boulder opal. "Jundah" means "woman" in the native language of the area (thanks to 1nn1 for the translation).

Answer: Ethiopia

In 1994, a rich deposit of opal was discovered in the Menz Gishe District, North Shewa Province, Ethiopia. Sources conflict as to how much opal is extracted from Ethiopia, especially as compared to Australia (which still predominates, of course). Most of the rest of the planet's opal digs are in the Americas, especially in the USA, Mexico, Peru, and Brazil. In the USA, the most productive mines are in Virgin Valley, Nevada, but there are also opal mines in Arizona, Oregon, Idaho, and Montana. There are also smaller opal deposits in the Czech Republic, Slovakia, Turkey, and Indonesia.

Answer: Mars

In 2008, opal deposits were discovered on our neighboring planet Mars. The meteorite Nakhla, composed of volcanic rocks over a billion years old, provided definite proof. What made this discovery particularly interesting to astronomers and cosmologists is that the opal deposits are an indication that life existed once on Mars, since water is required for opal to form, and the opal areas on Mars are good places to begin exploration for evidence of life. If there were microbes on Mars, they may have even be preserved in the opal on the Red Planet.

Answer: True

Not only does Australia have opalized fossils, it is in fact the only place on Earth where one can find opalized fossils of land animals, including the dinosaurs. And most of these were dug up from Lightning Ridge, Australia's main source of black opal. (Other Australian opal fields have opalized fossils of marine reptiles like icthyosaurs and pleiosaurs, but not dinosaurs.) The animals were thought to have lived near the South Pole.

Some of the opalized dinosaur bones are in fact transparent (just as some opals are); these are the only see-through large animal bones ever found.