Most people know precious gemstones (宝石) by their appearances. An emerald flashes deep green, a ruby seems to hold a red fire inside, and a diamond shines like a star. It’s more difficult to tell where the gem was mined, since a diamond from Australia or Arkansas may appear the same to one from the Democratic Republic of the Congo. However, recently, a team of scientists has found a way to identify a gemstone’s origin.
Beneath the surface of a gemstone, on the tiny level of atoms and molecules（分子）, lie clues (线索) to its origin. At this year’s meeting of the Geological Society of America in Minneapolis, Catherine McManus reported on a technique that uses lasers (激光) to clarify these clues and identify a stone’s homeland. McManus directs scientific research at Materialytics, in Killeen, Texas. The company is developing the technique. “With enough data, we could identify which country, which mining place, even the individual mine a gemstone comes from,” McManus told Science News.
Some gemstones, including many diamonds, come from war-torn countries. Sales of those “blood minerals” may encourage violent civil wars where innocent people are injured or killed. In an effort to reduce the trade in blood minerals, the U.S. government passed law in July 2010 that requires companies that sell gemstones to determine the origins of their stones.
To figure out where gemstones come from, McManus and her team focus a powerful laser on a small sample of the gemstone. The technique is called laser-induced breakdown spectroscopy. Just as heat can turn ice into water or water into steam, energy from the laser changes the state of matter of the stone. The laser changes a miniscule part of the gemstone into plasma, a gas state of matter in which tiny particles（微粒）called electrons separate from atoms.
The plasma, which is superhot, produces a light pattern. (The science of analyzing this kind of light pattern is called spectroscopy.) Different elements produce different patterns, but McManus and her team say that gemstones from the same area produce similar patterns. Materialytics has already collected patterns from thousands of gemstones, including more than 200 from diamonds. They can compare the light pattern from an unknown gemstone to patterns they do know and look for a match. The light pattern acts like a signature, telling the researchers the origin of the gemstone.
In a small test, the laser technique correctly identified the origins of 95 out of every 100 diamonds. For gemstones like emeralds and rubies, the technique proved successful for 98 out of every 100 stones. The scientists need to collect and analyze more samples, including those from war-torn countries, before the tool is ready for commercial use.
Scientists like Barbara Dutrow, a mineralogist from Louisiana State University in Baton Rouge, find the technique exciting. “This is a basic new tool that could provide a better fingerprint of a material from a particular locality,” she told Science News.
66. We learn from Paragraph 1 that __________.
A. an emerald and a ruby are names of diamonds.
B. it’s not difficult to tell where the gem was mined.
C. appearances help to identify the origin of gemstones.
D. diamonds from different places may appear the same.
67. Why did the U.S. government pass law that requires companies selling gemstones to determine the origins of their stones?
A. To look for more gemstones.
B. To encourage violent civil wars.
C. To reduce the trade in blood minerals.
D. To develop the economy.
68. Which of the following facts most probably helps McManus and her team in identifying the origin of stones?
A. Heat can turn ice into water or water into steam.
B. Gemstones from the same area produce similar light patterns.
C. Laser can change a miniscule part of the gemstone into plasma.
D. Materialytics has already collected patterns from thousands of gemstones.
70. From the last two paragraphs, what can be inferred about the laser technique?
A. It is ready for commercial use.
B. People can use the new tool to find more gemstones.
C. It can significantly reduce the gemstones trade in blood minerals.
D. It will bring about a revolutionary change in identifying the origin of minerals.
70. The author wrote this passage mainly to __________.
A. tell us how to identify the origin of diamonds.
B. introduce a laser technique in identifying a stone’s origin
C. prove identifying the origin of gemstones are difficult
D. attract our attention to reducing trade in blood minerals