Synthetic Gemstones
For centuries, humans have been fascinated by gems because of their rarity, durability, and beauty. Efforts to produce imitation gemstones go far back into history also. Charlatans have long tried to pass off as the real thing minerals that only looked like true gemstones.
The first attempts to produce gemstones in the laboratory occurred in the 1830s. French chemist Marc Gaudin (1804-1880), tried melting chemical compounds that would decompose to produce aluminum oxide, the compound of which rubies are made. Gaudin added a small amount of chromium to impart the characteristic color of the ruby. Although he did not realize it at the time, Gaudin was successful in producing a few tiny crystals of ruby.
In 1904 French scientist Auguste Verneuil (1823-1895) was more successful. Verneuil invented a special furnace for first melting a raw material, such as aluminum oxide, and then allowing it to cool slowly. When an impurity such as chromium, titanium, or iron was added to the molten material, Verneuil's process yielded synthetic rubies or sapphires. When magnesium oxide was used in place of aluminum oxide, spinel, emerald, aquamarine, blue zircon, green tourmaline, or milky moonstone was the product. Verneuil's process is still in use today. In all, about one-hundred different synthetic minerals and gemstones can be produced by the method.
The Verneuil process, however, cannot be used to produce some gemstones, such as opal. Opal can be synthesized by producing tiny spheres of silica in a chemical reaction and then bonding the spheres together by compression.
The greatest amount of effort to produce synthetic gemstones has probably been devoted to the manufacture of synthetic diamonds. Diamonds are an important material for both jewelry and industrial cutting applications. Neither of the methods described above can be used in the production of synthetic diamonds. The technique that is used mimics the process by which diamonds are produced naturally in the earth.
Scientists believe that diamonds (a form of pure carbon) are produced when other forms of carbon are subjected to very high temperatures and pressures at depths of 90-120 mi (145-200 km) beneath the Earth's surface. Based on laboratory research, they think that temperatures of at least 2,700°F (1,482°C) and pressures of 975,000 lb per sq in (66,300 atmospheres) are involved in the creation of natural diamonds.
As far back as the 1850s, scientists attempted to produce temperatures and pressures in the laboratory that would be sufficient to convert graphite to diamond. Scottish chemist James Hanney, French chemists Charles Friedel (1832-1899) and Ferdinand Moissan (1852-1907), British engineer Charles Parsons, and American inventor Edward G. Acheson, were only a few of those who tried--and failed--to find a method for synthesizing diamonds.
That breakthrough finally occurred on December 16, 1954. Working with a high-pressure device invented by Percy Bridgman, a research team at General Electric's Research Laboratories, under H. Tracy Hall, was able to convert graphite powder into tiny diamond crystals. The team used Bridgman's diamond anvil cell to produce a temperature of more than 4,800°F (2,649°C) and a pressure of more than 1.5 million lb per sq in (100,000 atmospheres) to achieve success.
The General Electric process is still used to produce tens of thousands of pounds of diamonds with little gemstone value, but with great industrial importance. In 1970, the General Electric process was improved and refined to allow the production of carat-size diamonds. The process is too expensive, however, to make these diamonds competitive with natural diamonds.
In 1984, the diamond anvil cell was employed to manufacture yet another gemstone, jadeite. Robert C. De Vries and James F. Fleischer, at the General Electric Research and Development Center, used a pressure of 440,000 lb per sq in (30,000 atmospheres) and a temperature of 2,700°F (1,482°C) to convert a mixture of sodium, aluminum, and silicon oxides to jadeite. They were able to produce crystals.25 in (6.35 mm) thick and.5 in (12.7 mm) long colored green (when chromium was added), lavender (when manganese was added), or banded with the two colors.
Not all methods of producing synthetic gemstones are safe. One method involves bombarding stones with neutrons in a nuclear reactor. In 1997, a number of chrysoberyl cat's eye gems found in Hong Kong were made by this method. The procedure converted the initial stones from yellow to brown and made them worth thousands of dollars more per carat. Although this procedure increased the value of the gems, it also caused them to emit radioactivity at dangerous levels. Authorities found most of these radioactive stones and confiscated them.
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