This article describes how the worldwide markets for opals, sapphires, and emeralds are affected by discoveries of new sources of gems.
TUCSON — Every February, gem and mineral dealers from around the world flock to this city in the Arizona desert (…). The critical factor in determining a favored new gemstone is not color, as many people might suspect. Rather, it is quantity. In other words, is the gem available in volumes substantial enough to support a commercial trade? “It all depends on what’s coming out of the ground,” said Divyanshu Navlakha, co-owner of Sutra, a jeweler based in Houston that specializes in high-end colored stone designs.
By these standards, an enchanting variety of white opal from the Wollo Province of Ethiopia was Tucson’s undisputed winner. (…) Discovered in 2008, the Wollo [opals] made their first major appearance in Tucson in 2010, when only a handful of dealers had access to the material. Over the past four years, however, more merchants — charmed by the gems’ lively appearance, their affordability and, of course, their abundance — have gotten in on the action. The subsequent rush has driven wholesale prices up by at least a factor of three.
“When it first came out, it was new, fun, exciting and cheap — and rarely do you get all those things in the same sentence,” said Jerry Romanella, co-owner of Commercial Mineral, a Phoenix-based gem dealer that has sold Ethiopian opals in large quantities since 2010.
“It used to be $35 to $125 per carat,” Mr. Romanella said. “Now, a very nice pretty Ethiopian opal is $100 to $300 a carat, so it’s catching up with the Australian.”
And therein lies the rub. Australia is the classic source of gem-quality opal. Legendary deposits such as Coober Pedy and Lightning Ridge have long supplied the market with gems ranging from low-cost white opal beloved by the jewelry television channels to fiery black opals worth as much as $300,000 at wholesale for a single spectacular stone.
Given how invested many Australian dealers are in opals, it did not come as a surprise in Tucson that some of them began grumbling about the competition from East Africa. (…) “Of course they’re threatened,” said Simon Watt, co-owner of Mayer & Watt, a gem dealer in Maysville, Ky. “They’ve controlled the market for 50 years, and now there’s a huge deposit in another market, and they can’t control it.” (…)
The trade confronted the issue in 1998, when a mother lode of sapphires — in a rainbow of hues, including blue, pink, yellow, and purple — was discovered near the village of Ilakaka in southwestern Madagascar. “There was a lot of it and it was starting to change the price structure and availability of certain colors of sapphires,” Mr. Robertson said. (…)
1) Explain, using supply analysis, the underlined sentence. 2) Explain, using supply and demand analysis, why Australian dealers were unhappy about the discovery of opals in Ethiopia. 3) What determines the willingness to pay for gems? 4) Do you think that the high reputation of gems from particular origins necessarily reflects true differences in quality? Could we see bubbles in markets for gems?
Source : manuel en ligne core.econ, chapitre 9 Market dynamics, p. 28
 A gem : une pierre précieuse.  An emerald: une émeraude.  To flock to : affluer vers  To own : posséder ; an owner : un propriétaire  A jeweler : un bijoutier (jewellery : bijoux)  Therein : à cet égard, à cet endroit ;  The rub : l’obstacle, le problème  Willingness to pay : consentement à payer