GOLD (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Gold has been called the most beautiful of all chemical elements. Its beauty has made it desirable for use in jewelry, coins, and artwork for thousands of years. It was one of the first pure metals to be used by humans.

Gold is one of the few elements that can affect politics and economics. Wars have been fought over access to gold. Cities and towns have sprung up and died out as gold was discovered and then mined out. Many nations still count their wealth according to the amount of gold they keep in storage.

Gold lies in the middle of the periodic table. The periodic table is a chart that shows how elements are related to one another. Gold is a heavy metal in a group known as the transition metals. Gold is also known as a precious metal (as are platinum and silver).

Large amounts of gold are still used in the manufacture of coins, medals, jewelry, and art. Gold also has a number of uses in industry, medicine, and other applications. For example, one radioactive isotope of gold is commonly used to treat cancer.

SYMBOL
Au

ATOMIC NUMBER
79

ATOMIC MASS
196.9665

FAMILY
Group 11 (IB)
Transition metal

PRONUNCIATION
GOLD

The chemical symbol for gold is Au. The symbol comes from the Latin word for gold, aurum. Aurum means "shining dawn."

Discovery and naming

Gold objects dating to 2600 b.c. have been found. They were discovered in the royal tombs of the ancient civilization of Ur. These objects showed that humans had already learned how to work with gold this early in history. Some of the gold, for example, had been formed into wires.

One of the special skills developed by the Egyptians was the adding of gold to glass objects. They found a way to use gold to make glass a beautiful ruby-red color. The glass became known as gold ruby glass.

Gold is also mentioned in a number of places in the Bible. A passage in Exodus, for example, refers to the clothing worn by Aaron: "And they did beat the gold into thin plates, and cut it into wires, to work it in the blue, and in the purple, and in the scarlet, and in the fine linen, with cunning work."

Writings from every stage of human history tell of the discovery and use of gold. Roman historian Pliny the Elder (a.d. 23-79), for example, describes gold-mining locations. The Romans found it lying in stream beds in the Tagus River in Spain, the Po River in Italy, the Hebrus River in Thracia (now Greece), the Pactolus River in Asia Minor (now Turkey), and the Ganges River in India.

Goin' for the silver and gold!

O ne of the most famous items using gold is the Olympic gold medal. Athletes from around the world dream of coming in first place at the Olympics. That means they can step up to the winner's podium and wear their gold medal proudly. But the gold medal isn't solid gold. It's actually made out of silver. A thin layer of gold covers the silver. The last time a solid gold medal was used in the Olympics was 1912.

Christopher Columbus found gold nuggets lying in the bottom of rivers and harbors in Haiti.

Gold has long been known in the New World, too. During a visit to Haiti, Christopher Columbus (1451-1506) found gold nuggets lying on the bottom of rivers and harbors. A Portuguese explorer in 1586, Lopez Vaz, wrote that the region called Veragua (now Panama) was the "richest Land of Gold [in] all the rest of the Indies."

In the United States, of course, the most famous story about gold occurred in the late 1840s. Thousands of people flocked to California in search of gold. This era was called the Gold Rush. People became very rich or found nothing at all during this exciting time in history.

Physical properties

Gold is both ductile and malleable. Ductile means it can be drawn into thin wires. Malleable means capable of being hammered into thin sheets. A piece of gold weighing only 20 grams (slightly less than an ounce) can be hammered into a sheet that will cover more than 6 square meters (68 square feet). The sheet will be only 0.00025 centimeters (one ten-thousandth of an inch) thick. Gold foil of this thickness is often used to make the lettering on window signs.

Gold is quite soft. It can usually be scratched by a penny. Its melting point is 1,064.76°C (1,948.57°F) and its boiling point is about 2,700°C (4,900°F). Its density is 19.3 grams per cubic centimeter.

Two other important properties are its reflectivity and lack of electrical resistance. Both heat and light reflect off gold very well. But an electric current passes through gold very easily.

Chemical properties

Generally speaking, gold is not very reactive. It does not combine with oxygen or dissolve in most acids. It does not react with halogens, such as chlorine or bromine , very easily.

These chemical properties also account for some important uses of gold. Gold coins, for example, do not corrode (rust) or tarnish very easily. Neither does jewelry or artwork made of gold.

Occurrence in nature

Gold occurs in nature in both its native state and in compounds. The native state of an element is its free state. It is not combined with any other element. The most common compounds of gold are the tellurides. A telluride is a compound of the element tellurium and one or more other elements. For example, the mineral calavarite is mostly gold telluride (AuTe₂).

At one time, gold was found in chunks or nuggets large enough to see. People mined gold by picking it out of streams and rivers. In fact, gold was once very common in some parts of the world. People valued it not because it was rare, but because it was so beautiful.

The abundance of gold in the Earth's crust is estimated to be about 0.005 parts per million. That makes it one of the ten rarest elements in the Earth's crust. Gold is thought to be much more common in the oceans. Some people believe as much as 70 million tons of gold are dissolved in seawater. They also think there may be another 10 billion tons on the bottom of the oceans. So far, however, no one has found a way to mine this gold.

About a quarter of the world's gold comes from South Africa. Other leading producers of the metal are the United States, Australia, Canada, China, and Russia. In the United States, about two-thirds of its gold is mined in Nevada. California, Montana, Alaska, and South Dakota also produce gold.

The Gold Rush!

T he most famous story about gold in the United States might be the Gold Rush of 1849. As early as the sixteenth century, records contained stories about a great El Dorado ("the gilded one," in Spanish; gilded means "covered in gold") on the western coast of the United States. Tales of this magical city were repeated for centuries.

In the late 1840s, explorers began to travel from the Eastern seaboard to California in search of El Dorado. The flow of visitors was slow at first. Gold was first discovered in 1848 at a place called Sutter's Mill. Sutter's Mill was located near the present town of Coloma, California.

Word of the discovery spread quickly. Within a year, thousands of men and women made the long, expensive, and tiring trip. Most people traveled across the United States in covered wagons or on horseback. Many of them had to cross mountains, plains, and deserts. Because of the difficult conditions, many people and animals got sick or died. Some people traveled around Cape Horn at the bottom of South America or across the Isthmus of Panama. No matter which route was used, the journey usually took months.

As people arrived in California, hundreds of mining camps sprang up. Some of them had colorful names. Poker Flat, Hangtown, Red Dog, Hell's Delight, and Whiskey Bar were just a few! Mining for gold was hard work. Gold miners usually wound up being wildly successful or terrible failures. The Gold Rush of 1849 completely changed the state of California. It also helped expand the United States.

At one time, gold was found in chunks or nuggets large enough to see.

Isotopes

There is only one naturally occurring isotope of gold, gold-197. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

About two dozen radioactive isotopes of gold are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

One radioactive isotope of gold is widely used in medicine, gold-198. This isotope has two major uses. First, it can be used to study the liver. It is made into a form known as colloidal gold. Colloidal gold consists of very fine particles of gold mixed in a liquid solution. The colloidal gold is injected into the patient's body, where it travels to the liver. There, it can be detected because of the radiation it gives off. The radiation can be used to tell if the liver is functioning normally or not.

In a 1986 study, experts estimated that 121,000 tons of gold had been mined throughout history.

Colloidal gold is also used to treat medical problems. In some forms of cancer, the body develops large amounts of liquid in the space around the stomach and intestines (the peritoneum). One way to treat this collection of liquid is with colloidal gold. The colloidal gold is injected into the peritoneum.

It is not able to Leave the peritoneum and go into the stomach and intestines. While in the peritoneum, the colloidal gold gives off radiation. The radiation kills cancer cells that cause the accumulation of fluid.

Extraction

There are at least two main ways to remove gold from its ores. One is to mix an ore with mercury metal. Mercury combines with gold in the ore to form an amalgam. An amalgam is a mixture of two or more metals, one of which is mercury. The gold amalgam is then removed from the ore. It is heated to drive off the mercury. Pure gold remains.

Measuring gold

Which weighs more: A pound of feathers or a pound of gold? Teachers sometimes try to fool students with this old question. The answer would seem to be easy: a pound is a pound. A pound of feathers and a pound of gold should weigh the same amount.

But that is not quite true. In the English system, most substances are measured using the avoirdupois (pronounced a-verde-POIZ) system. In the avoirdupois system, there are 16 ounces to the pound.

But gold is weighed differently. It uses the troy system. In the troy system, one pound contains only 12 ounces. So, a pound of feathers (avoirdupois system) weighs four ounces more than a pound of gold (troy system). The weight of other precious metals, like silver and platinum, are also measured using the troy system.

Gold is also weighed in carats. A carat is defined as one fifth of a gram, or 200 milligrams.

Gold is seldom used in a pure form. The metal is too soft. It would bend or break if used pure. Instead, it is used in combination with other metals called alloys. An alloy is a mixture of two or more metals. The mixture has properties different from those of the individual metals.

The amount of gold in an alloy is expressed in carats. Pure gold metal (mixed with no other metal) is said to be 24-carat gold. An alloy that contains 20 parts of gold and 4 parts of silver is 20-carat gold. The "20-carat" designation means the alloy contains 20 parts of gold and 4 parts of something else (silver, in this case).

Gold stored in a national bank can be 24-carat gold. It is never used for any practical purpose. But gold used for any real application is almost always less than 24 carats. It must include other metals that make it stronger and tougher.

Gold ores can also be treated with potassium cyanide (KCN) or some other kind of cyanide. The gold combines with the cyanide to form a new compound, gold cyanate. The gold cyanate is then treated with an active metal, such as zinc. The active metal replaces gold in the compound, leaving pure gold.

Uses

In a 1986 study, experts estimated that 121,000 tons of gold had been mined throughout history. Of that amount, about 18,000 tons were used for industrial, research, health, and other "dissipative" uses. Dissipative means that the gold was gone once it was used. It was made into devices that were eventually thrown away. The gold could not or was not recovered from the devices.

Of the remaining 103,000 tons of gold, about a third (35,000 tons) had been made into gold bars held by national banks. The gold bars are used as security for national money systems. In the United States, for example, the nation's supply of gold is stored at Fort Knox, Kentucky.

Finally, the remaining 68,000 tons of gold are owned by private individuals. This gold exists in the form of jewelry, coins, or bullion. Gold bullion are bars or other large pieces of pure gold.

Jewelry is the largest single use of gold. In 1996, about 3,290 tons of gold were made worldwide. Of that amount, nearly 85 percent was made into jewelry. The second largest use of gold (about 213 tons, or about 7 percent) was in industrial devices and consumer products. Some examples include electrical contacts and switches, laboratory equipment, printed circuits, dental alloys, instruments on space vehicles, and nozzles used in the production of synthetic fibers.

Compounds

Few gold compounds have any important commercial uses.

In the United States, the nation's supply of gold is stored at Fort Knox, Kentucky.

Health effects

Gold is not required to maintain good health in plants or animals. It can be injected into a plant or animal without causing harmful effects. Some medical and commercial uses are based on this property.

Gold

BIBLIOGRAPHY

Gold is a precious metal. Its several qualities have made it valuable throughout history. It is an attractive color (yellow), bright, malleable, and workable in various forms. It is also long-lasting and tough. All these properties have made it the metal of choice for decoration and art objects. Gold has also been the standard of wealth for seven thousand years, dating from the time of the ancient civilizations of Egypt and Mesopotamia. More recently, gold has become the standard of currencies.

Gold is found across a wide range of the earth’s landscape, but its accumulation in large quantities dates from the era of European explorations that began in the middle of the fifteenth century. Ventures to the New World opened new chapters in the history of gold. The first of these new stages was the Spanish conquest of the Americas with the accompanying destruction of the Aztec and Incan civilizations. Within a generation, these expeditions of plunder had produced an outpouring of gold from the New World that astonished the Old and led to endless expeditions of discovery and conquest, all in search of the legendary golden city known as El Dorado. Over the seventeenth and eighteenth centuries, the gold flowing out of the South American mines continued to dominate world production. As the nineteenth century unfolded, Russia became the leading producer. By 1847 Russia was the source of about three-fifths of the gold mined annually in the world.

The second great era of gold production was associated with major discoveries in California and Australia in the middle of the nineteenth century. In addition to the large quantities of gold harvested, these discoveries led to a new departure in the history of gold. Heretofore, gold discoveries and the gold mined from them had been a monopoly of the state. California and Australia represented a dramatic change in the sense that these mid-nineteenth century bonanzas belonged to any individual who could stake a claim. In this fashion, the gold passed directly into the hands of private citizens (or noncitizens, as was frequently the case). California’s gold production moved rapidly from $10 million in 1849 to $80 million in 1851, thereafter settling at about $40 million annually. California almost immediately produced half the world’s supply. Within the first five years, California produced as much gold as the Roman Empire had taken from the mines in northern Spain in half a century. The yields in Australia were almost as great. The Australian gold rush, like that of California, had a short life. After a dozen years, gold mining became industrialized. Still, the returns were remarkable. In the quarter century from 1850 to 1875, more gold was produced than in all the years since 1492, almost all of it in California and Australia.

The gold discoveries and the availability of these riches to anyone led to a remarkable rise in the numbers of miners. In California, the numbers rose from perhaps 5,000 in 1848 to 125,000 in 1851. This harvesting of gold on such a scale changed California from an isolated pastoral community into the most cosmopolitan place in the world. By 1852 its population had passed 250,000 people. California now became a pioneer in new patterns of rapid and intense migration associated with mining. These would include the astonishing rise of towns (and sometimes cities), the recruitment and use of labor forces, and shifts in capital and labor to remote areas all over the world. Such phenomena appeared first in California and Australia. The arrival of overseas Chinese, Irish, and other northern European immigrants in the gold fields created a diverse population and led to later racial strife. In both Australia and the mining camps of the American West, the Chinese were a particular target. Everywhere, whatever the racial and ethnic composition, mining camps were intensely male. Only gradually did the emerging towns come to include women and children.

At the same time, the techniques used to harvest the gold changed in decisive ways. Mining in California began with picks, pans, and shovels, as individuals and small companies washed gold from mountain streams. Within a few short years, gold mining had progressed to damming (then mining dry river beds), to hydraulic mining (using water streams to wash away hills), and to underground mining. What had begun as the work of individual miners had within a dozen years become an extension of industrial techniques, with wage laborers deep underground, complex processing machinery and plants above ground, and a stock market that enabled absentee investors to speculate.

These bonanzas of the 1850s enormously increased the world’s supply of gold. The gold reserves in the Bank of England almost doubled between 1848 and 1852; the gold inventory of the Bank of France increased seven times. Thus, the impact of the Californian and Australian gold rushes was quickly reflected in the gold reserves of Britain, France, and other powerful European nations. Great wealth also accrued to individuals and companies of various sizes. This increase led to extended debate within financial circles about the role of gold in the currencies of individual nations and the significance of gold as a worldwide standard.

The third great increase in the world’s supply was associated with gold discoveries in Alaska at the close of the nineteenth century and in South Africa at the opening of the twentieth century. The Alaskan strikes began as a reprise of the Californian dream of riches for individuals and small groups, then rapidly shifted to production by well-financed companies with the latest equipment, all within the context of a climate that severely limited the mining season. In South Africa, the gold discoveries laid the basis of some of the more remarkable mineral fortunes in the world. They also established a labor system in which thousands of black Africans labored deep in the mines for the benefit of a few white-owned South African companies. The increase in gold production in these years was notably aided by a new chemical process, the use of cyanide to recover gold from low-grade ores.

The flooding of gold into Europe at the opening of the sixteenth century and in the middle of the nineteenth century raised continuing questions about national currencies. Over the course of the nineteenth century, most major Western nations went on the gold standard; that is to say, their national currency acquired a fixed relation to gold and was supposedly freely convertible into gold at that price. England was the first to adopt the gold standard, in 1821. France, Germany, Spain, and the United States followed in the 1870s. The gold standard spread across Europe, but ended with the outbreak of war in 1914. It was reinstituted in 1928. As national economies grew, nations without sufficient gold reserves (the majority of nations) supplemented their currency reserves with U.S. dollars or British pounds, thought to be the most stable of the world’s currencies. With the onset of the Great Depression, the gold standard collapsed again. Although it was restored after the war, the dominance of the U.S currency (the dollar) and dwindling gold reserves led to the gold standard’s abandonment in 1971.

SEE ALSO Gold Industry

BIBLIOGRAPHY

Green, Timothy. 1973. The World of Gold Today. Rev. ed. New York: Walker & Company.

Hawtrey, R. G. 1948. The Gold Standard in Theory and Practice. 5th ed. London: Longmans.

Jastrom, Roy W. 1977. The Gold Constant: The English and American Experience, 1560–1976. New York: John Wiley & Sons.

Kettell, Brian. 1982. Gold. Cambridge, MA: Ballinger Press.

Rohrbough, Malcolm. 1997. Days of Gold: The California Gold Rush and the American Nation. Berkeley: University of California Press.

Vilar, Pierre. 1976. A History of Gold and Money, 1450–1920. Trans. Judith White. London: Atlantic Highlands Press.

Malcolm Rohrbough

Gold

Background

Gold, recognizable by its yellowish cast, is one of the oldest metals used by humans. As far back as the Neolithic period, humans have collected gold from stream beds, and the actual mining of gold can be traced as far back as 3500 b.c., when early Egyptians (the Sumerian culture of Mesopotamia) used mined gold to craft elaborate jewelry, religious artifacts, and utensils such as goblets.

Gold's aesthetic properties combined with its physical properties have long made it a valuable metal. Throughout history, gold has often been the cause of both conflict and adventure: the destruction of both the Aztec and Inca civilizations, for instance, and the early American gold rushes to Georgia, California, and Alaska.

The largest deposit of gold can be found in South Africa in the Precambrian Witwatersrand Conglomerate. This deposit of gold ore is hundreds of miles across and more than two miles deep. It is estimated that two-thirds of the gold mined comes from South Africa. Other major producers of gold include Australia, the former Soviet Union, and the United States (Arizona, Colorado, California, Montana, Nevada, South Dakota, and Washington).

About 65 percent of processed gold is used in the arts industry, mainly to make jewelry. Besides jewelry, gold is also used in the electrical, electronic, and ceramics industries. These industrial applications have grown in recent years and now occupy an estimated 25 percent of the gold market. The remaining percentage of mined gold is used to make a type of ruby colored glass called purple of Cassius, which is applied to office building windows to reduce the heat in the summer, and to mirrors used in space and in electroscopy so that they reflect the infrared spectrum.

Physical Characteristics

Gold, whose chemical symbol is Au, is malleable, ductile, and sectile, and its high thermal and electrical conductivity as well as its resistance to oxidation make its uses innumerable. Malleability is the ability of gold and other metals to be pressed or hammered into thin sheets, 10 times as thin as a sheet of paper. These sheets are sometimes evaporated onto glass for infrared reflectivity, molded as fillings for teeth, or used as a coating or plating for parts. Gold's ability to be drawn into thin wire (ductility) enables it to be deposited onto circuits such as transistors and to be used as an industrial solder and brazing alloy. For example, gold wire is often used for integrated circuit electrical connections, for orthodontic and prosthetic appliances, and in jet engine fabrication.

Gold's one drawback for use in industry is that it is a relatively soft metal (sectile). To combat this weakness, gold is usually alloyed with another member of the metal family such as silver, copper, platinum, or nickel. Gold alloys are measured by karats (carats). A karat is a unit equal to 1/24 part of pure gold in an alloy. Thus, 24 karat (24K) gold is pure gold, while 18 karat gold is 18 parts pure gold to 6 parts other metal.

Extraction and Refining

Gold is usually found in a pure state; however, it can also be extracted from silver, copper, lead and zinc. Seawater can also contain gold, but in insufficient quantities to be profitably extracted—up to one-fortieth (1/40) of a grain of gold per ton of water. Gold is generally found in two types of deposits: lode (vein) or placer deposits; the mining technique used to extract the gold depends upon the type of deposit. Once extracted, the gold is refined with one of four main processes: floatation, amalgamation, cyanidation, or carbon-in-pulp. Each process relies on the initial grinding of the gold ore, and more than one process may be used on the same batch of gold ore.

Mining

• 1 In lode or vein deposits, the gold is mixed with another mineral, often quartz, in a vein that has filled a split in the surrounding rocks. Gold is obtained from lode deposits by drilling, blasting, or shoveling the surrounding rock.

  Lode deposits often run deep underground. To mine underground, miners dig shafts into the ground along the vein. Using picks and small explosives, they then remove the gold ore from the surrounding rock. The gold ore is then gathered up and taken to a mill for refinement.

• 2 Placer deposits contain large pieces of gold ore (nuggets) and grains of gold that have been washed downstream from a lode deposit and that are usually mixed with sand or gravel. The three main methods used to mine placer deposits are hydraulic mining, dredging, and power shoveling. All methods of placer deposit mining use gravity as the basic sorting force.

  In the first method, a machine called a "hydraulic giant" uses a high pressure stream of water to knock the gold ore off of banks containing the ore. The gold ore is then washed down into sluices or troughs that have grooves to catch the gold.

  Dredging and power shoveling involve the same techniques but work with different size buckets or shovels. In dredging, buckets on a conveyor line scoop sand, gravel, and gold ore from the bottom of streams. In power shoveling, huge machines act like shovels and scoop up large quantities of gold-bearing sand and gravel from stream beds.

  Hydraulic mining and dredging are outlawed in many countries because they are environmentally destructive to both land and streams.

Grinding

• 3 Once the gold ore has been mined, it usually is washed and filtered at the mine as a preliminary refinement technique. It is then shipped to mills, where it is first combined with water and ground into smaller chunks. The resulting mixture is then further ground in a ball mill—a rotating cylindrical vessel that uses steel balls to pulverize the ore.

Separating the gold from the ore

• 4 The gold is then separated from the ore using one of several methods. Floatation involves the separation of gold from its ore by using certain chemicals and air. The finely ground ore is dumped into a solution that contains a frothing agent (which causes the water to foam), a collecting agent (which bonds onto the gold, forming an oily film that sticks to air bubbles), and a mixture of organic chemicals (which keep the other contaminants from also bonding to the air bubbles). The solution is then aerated—air bubbles are blown in—and the gold attaches to the air bubbles. The bubbles float to the top, and the gold is skimmed off.

  Cyanidation also involves using chemicals to separate the gold from its contaminants. In this process, the ground ore is placed in a tank containing a weak solution of cyanide. Next, zinc is added to the tank, causing a chemical reaction in which the end result is the precipitation (separation) of the gold from its ore. The gold precipitate is then separated from the cyanide solution in a filter press. A similar method is amalgamation, which uses the same process with different chemicals. First, a solution carries the ground ore over plates covered with mercury. The mercury attracts the gold, forming an alloy called an amalgam. The amalgam is then heated, causing the mercury to boil off as a gas and leaving behind the gold. The mercury is collected, recycled and used again in the same process.

  The carbon-in-pulp method also uses cyanide, but utilizes carbon instead of zinc to precipitate the gold. The first step is to mix the ground ore with water to form a pulp. Next, cyanide is added to dissolve the gold, and then carbon is added to bond with the gold. After the carbon particles are removed from the pulp, they are placed in a hot caustic (corrosive) carbon solution, which separates the gold from the carbon.

• 5 If the gold is still not pure enough, it can be smelted. Smelting involves heating the gold with a chemical substance called flux. The flux bonds with the contaminants and floats on top of the melted gold. The gold is then cooled and allowed to harden in molds, and the flux-contaminant mixture (slag) is hauled away as a solid waste.

The Future

Because gold is a finite resource, its long-term future is limited. In the short term, however, it will continue to find widespread use in jewelry and in industrial applications, especially in the electronics field.

In the last few years, several companies have focused on extracting gold from sulphide ore rather than oxide ore. Previous techniques made such extraction difficult and expensive, but a newer technique called bioleaching has made extraction more feasible. The process involves combining the sulphide ore with special bacteria that "eat" the ore or break it down into a more manageable form.

Where To Learn More

Books

Coombs, Charles. Gold and Other Precious Metals. Morrow Publishing, 1981.

Gasparrini, Claudia. Gold & Other Precious Metals: From Ore to Market. Springer-Verlag, 1993.

Green, Timothy. The World of Gold. Walker Publishing, 1968.

Hawkins, Clint. Gold & Lead. HarperCollins, 1993.

Lye, Keith. Spotlight on Gold. Rourke Enterprises, 1988.

McCracken, Dave. Gold Mining in the Nineteen Nineties: The Complete Book of Modern Gold Mining Procedure. New Era Publications, 1993.

Wise, Edmund, ed. Gold: Recovery, Properties, and Applications. Van Nostrand, 1964.

Periodicals

Abelson, Philip H. "Gold." Science. July 11, 1986, p. 141.

Dworetzky, Tom. "Gold Bugs." Discover, March, 1988, p. 32.

"Some Like It Hot." Economist. June 25, 1988, p.88.

"Mining with Microbes: A Labor of Bug." Science News. April 14, 1990, p. 236.

—Alicia Haley and

Blaine Danley

gold a yellow precious metal, the chemical element of atomic number 79, valued especially for use in jewellery and decoration, and to guarantee the value of currencies; taken as a type of something that is precious, beautiful, or brilliant.

The bullseye of an archery target is known as the gold.

The word is recorded from Old English, and is of Germanic origin, from an Indo-European root shared by yellow.
crock of gold a large but distant or imaginary reward, with allusion to the story of a crock of gold supposedly to be found by anyone reaching the end of a rainbow.
gold brick chiefly in the US, a thing that looks valuable, but is in fact worthless; from the confidence trickster's practice of preparing a block of base metal with a corner of gold to look like a brick-shaped piece of gold.
Gold Coast a former name (until 1957) for Ghana, so called because it was an important source of gold.
Gold Collar a classic greyhound race, inaugurated in 1933, run annually in September at the Catford track in south London, originally in May, now in September.
gold disc a framed golden disc awarded to a recording artist or group for sales of a recording exceeding a specified high figure. The figure varies from year to year and between countries; typical recent figures are, for a single, 500,000 in the UK or one million in the US, and for an album, 250,000 in the UK or 500,000 in the US.
gold may be bought too dear wealth may be acquired at too great a price; saying recorded from the mid 16th century.
gold rush a rapid movement of people to a newly discovered goldfield. The first major gold rush, to California in 1848, was followed by others in the US, Australia (1851–3), South Africa (1884), and Canada (Klondike, 1897–8).
gold standard the system by which the value of a currency was defined in terms of gold, for which the currency could be exchanged. The gold standard was generally abandoned in the Depression of the 1930s.
Gold Stick in the UK, a ceremonial officer in the Sovereign's household, entitled to carry a gilt rod on state occasions. The office is now held by the colonels of the senior household regiments in England and Scotland.

See also it is good to make a bridge of gold to a flying enemy, streets paved with gold at street.

Gold

melting point: 1,064.18°C
boiling point: 2,808°C
density: 19.32 g/cm³
most common ions: Au⁺ , Au³⁺,

Gold is a soft, malleable yellow metal . If finely divided, it may be black, ruby, or purple. The name of the element is derived from the Anglo-Saxon word geolo, meaning "yellow." The symbol Au is derived from the Latin word aurum, meaning "shining dawn."

Gold is the most malleable and ductile metal known. Approximately 28 grams (1 ounce) of gold can be hammered to form a piece that is 28 square meters (300 square feet). It is a good conductor of heat and electricity, and unreactive in air and most reagents . It forms ionic compounds primarily as a +3 ion; the most common compounds are gold (III) chloride (AuCl₃), and chlorauric acid (HAuCl₄).

The relative abundance of gold is 0.004 part per million (ppm) in Earth's crust. Deposits of the metal are found in South Africa, Siberia, North America, and South America. Gold has one naturally occurring isotope (¹⁹⁷Au) and forty-five synthetic isotopes.

Found in association with quartz or pyrite, gold occurs in veins and is traditionally isolated from rocks by panning or sluicing; these techniques take advantage of gold's high density. A modern method of isolation is the cyanide process, in which gold is leached from crushed rock with an aerated solution of sodium cyanide. The gold then precipitates upon addition of zinc dust and is purified by electrolytic refining.

Gold was used as early as the late Stone Age for ornamental purposes (e.g., jewelry and plating) and more recently as a monetary standard. It is a component of electrical connectors in computer equipment due to its high electrical conductivity. Its unreactivity in air leads to its use for corrosion-free contacts in electrical connections. As an excellent conductor of heat, it is used in the main engine nozzle of the space shuttle. Since gold is the most reflective of all metals, it is used as a coating for space satellites, face shields for astronauts, and windows. Chlorauric acid is used in photography; disodium aurothiomalate is given as a treatment for arthritis.

see also Inorganic Chemistry; Rutherford, Ernest.

Catherine H. Banks

Bibliography

Greenwood, Norman N., and Earnshaw, A. (1997). Chemistry of the Elements, 2nd edition. Boston: Butterworth-Heinemann.

Lide, David R., ed. (2003). "Gold." In The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.

Internet Resources

"Nothing Works Like Gold." The Gold Institute. Available from <http://www.goldinstitute.org>.