Printable Documents

Printable Documents: Copper: The Red Metal

Introduction

Copper has been used by human beings for at least 7,000 years. The island of Cyprus in the eastern Mediterranean was a major source of copper for the ancient world. Our word copper came from cuprum, the Roman name for Cyprian metal. Copper's symbol on the Periodic Chart of the Elements is Cu, an abbreviation of cuprum. Its atomic number is 29, and its atomic weight is 63.546.

In addition to the important copper deposits of Cyprus, copper is relatively common around the Mediterranean. It was found in nuggets and masses on the surface of the earth, adjacent to streams, in the walls of canyons. Although exposure to weather changes copper's reddish color to blue-green, it is easy to recognize. Ancient people learned that copper could be shaped by pressure, that is, it is "malleable."

Objects of beaten copper were used by the Chaldeans in the Middle East about 4500 B.C. Copper weapons and ornaments from about the same time have been found in the ruins of Susa, an ancient civilization located in the area of the nation that is now Iran. Native Americans exploited copper in the Upper Peninsula in Michigan perhaps 7000 years ago.

We have no way to know for certain how copper was discovered long ago. We know that humans already recognized gold. Maybe they were looking for other substances like gold. Maybe somebody dropped a piece of rock on some copper, and dented the copper without breaking it. Then, this clever ancient inventor might have realized that pure copper could be hammered into a useful or pretty shape. This special property of copper is called malleability.

Later, another observant person, maybe a potter, accidentally dropped a piece of copper in a fire. This early metal worker learned that the copper became less brittle and easier to shape if hammered after heating. This process is known as tempering.

Discovery of the idea of working copper also occurred in a number of cultures around the Earth. Thanks to the excellent archeological record in the arid southwest of Asia we know that ancient civilizations of Mesopotamia, especially the city-states of Sumeria, were among the earliest to invent the use of copper and gold. This area is now in the nation of Iraq.

Early History of Copper Mining and Use

The use of copper and gold marked the transition from the Stone Age to a more modern way of life. Ancient civilizations could use copper because it is found in its native state on the surface of the ground, because it has a distinctive color, and because it is easily worked.

Early Smelting and Metallurgy

As we have seen, the invention of metallurgy involved at first the simple beating of malleable copper into the shape desired. It was discovered that heating, called annealing, made copper more malleable, a process called tempering. The copper was hammered after it was heated. The resulting edge on a tool or weapon was harder and more durable.

Shaping of copper was also accomplished by cutting or grinding with abrasive stones, with such hard minerals as corundum.

Most copper is not found in its native state, that is, as a pure reddish brown metal. Usually, the copper is combined with other substances to make a mineral. Minerals may include the purplish cuprite, a combination of copper and oxygen, but most often, it is a green or blue mineral where copper is combined with other substances besides oxygen. When copper is in a mineral, it cannot be used as copper. It cannot be hammered or bent into another shape. Smelting copper ore to separate the copper from copper minerals required a hotter fire than normal cooking fires. It also required easily melted copper-bearing ore minerals such as green malachite and blue azurite or purplish red cuprite. The hotter fire was known by some cultures already, due to the development of fired pottery in a kiln. Probably by accident, it was discovered that the blue or green or purplish stones could be reduced to liquid copper metal in a fire. The fire must be hotter than a normal campfire, so there are two likely explanations for the discovery of smelting:

A potter left some blue-green stones in her kiln, perhaps to prop up a pot;
Or a campfire in a canyon became unusually hot due to the draft of air fanning it.

The primitive process of extracting metallic copper from copper-bearing stones by melting it is called smelting. Working with metal to extract it from ore and to form it into useful objects is called Metallurgy.

Copper was extracted from ore such as the mineral malachite. Ore is a mineral or aggregate of minerals from which a substance, usually a metal, can be extracted at a profit.

Shaping copper by casting it, that is, by pouring molten liquid copper into a mold, also first happened before anyone wrote it down, or even could write it down. Perhaps a bit of liquid metal ran into a footprint in the dirt by a campfire, where it formed a perfect cast of the footprint.

Smelting was used as well to make bronze, an alloy. Alloys are mixtures of metals. Bronze is an alloy of copper and tin.

Smelting was accomplished initially in an open fire. A hole one to two feet in diameter was dug in the ground. The hole was lined with fire-resistant clay or stone. Charcoal was placed in a layer on top of the clay, then was covered by copper ore. Charcoal burns particularly hot, raising temperatures enough to melt the copper. The charcoal also releases gases that react with the copper minerals to reduce them to copper metal. A molten mass of the dense copper formed, topped by lighter waste products, or slag. When the mass was cool, the brittle, glassy slag could be broken off, leaving a cake of refined copper behind. The furnace in this method is called an open hearth. Remnants of open hearths have been found in Sumerian ruins.

A more complex method used the crucible, a ceramic pot into which the charcoal and copper ore were placed. The crucible was placed into a fireplace, or furnace. Bellows, often made of goat skins, directed a draft of air to raise the temperature. The copper cake produced by this method was cleaner than that in the open hearth. Copper ingots were cast into the shape of bars, rings, and other shapes suitable to be transported to Sumerian cities.

Mining Techniques

Before you can beat or smelt or cast copper, it must be taken from the ground. In the beginning of mining, people simply picked up pieces of copper or gold, two metals that have a distinctive color, are found in large masses, and can be worked with primitive tools such as stone axes and hammers.

As civilizations began to use and depend on metals, the amount of pure copper or copper minerals found right at the surface was not enough anymore. Other ways of obtaining copper had to be developed.

These earliest miners quickly realized that some copper minerals exposed on the surface were the tip of a deposit going down into the earth. Using stone, and later copper and bronze implements, the miners dug down to follow the deposit. The implements were crude picks, hammers, chisels and shovels. Since no method of blasting was available, miners were confined to much slower and more tedious methods of opening the rock wall or face. The miners picked at loose stones with their tools. If no cracks or loose stones were available, fire was used to create sudden changes of temperature to crack the rock. Logs were piled against the rock face, then set afire. When the rock was very hot, the fire was quenched with water. Then miners used their tools to pull out the loosened rock.

Sometimes the miners followed loose nuggets of ore in gravel, called placers. Some metals make placers better than others. Gold makes excellent placer deposits because it tends not to react with air or water. Copper placers are less common. Tin, needed for bronze, makes excellent placers, while silver rarely is found as a placer deposit. Sometimes the miners followed veins into the solid rock, called lode deposits.

In Egypt, a great interest in gold drove exploration for mineral deposits south into Nubia (presently the nation of Sudan). Mining technology also improved. Excavations of large rooms underground, called stopes, were supported by pillars of unmined rock, or even by stone walls. Torches and oil lamps supplied a flickering, smoky light. Ventilation in these underground workings was very poor.

Slaves, prisoners of war, and criminals were forced to labor in the mines. Skeletons of those killed by falling rocks have been found, left buried where they died. Children would carry the pieces of ore to the surface in baskets strapped to their back. Once the ore reached the surface, other people who were too frail to work underground sorted the ore into richer and poorer pieces. Ore was moved by caravan to trade routes on the rivers, the Tigris, Euphrates, and Nile.

Early Civilizations and Copper

Besides areas in Western Asia, the use of copper was discovered in England where copper is found in Cornwall and Devon, western France, Italy, Spain, and central Europe in Saxony and Bohemia. Native American copper implements are known from Michigan, as well. Asian civilizations, too, discovered ways to use copper.

Back in the Middle East, the Sumerian city-states comprised the first great metal-using civilization. The Sumerians navigated the Euphrates River for commerce, including the transportation of copper from Armenia to the north. The Sumerian word for copper, "urudu", is the same word for the Euphrates, literally, their "copper river."

At Gerza on the Nile River just south of the modern site of Cairo, the Gerzeans developed a civilization based on the metallurgy of copper. In about 3500 B.C. they learned basic copper metallurgy from immigrants from Mesopotamia.

The First Dynasty of Egypt began about 200 years later, under King Menes. The tomb of the queen of Pharoah Snefru of the Second Dynasty contained copper stoneworking tools. It was not until the Third Dynasty, however, that the great stone tombs and monuments were begun. The pyramids and other great buildings of the Egyptian civilization were built of stones that had been quarried and shaped using copper tools.

While the rock used in the buildings was found nearby, the Eygptians mined copper in the Sinai Peninsula. The scale of copper mining in the Sinai reached a size that made it the first real industry of the ancient world. The Egyptians mined deposits of the green copper mineral malachite. Malachite, a copper carbonate, was prized because it was the easiest copper mineral to reduce to copper metal. The closely related blue copper carbonate mineral azurite also was discovered. Near these two copper ore minerals, the early prospectors often found another copper mineral, blue-green turquoise. Turquoise is still prized around the world as a gem stone. Ruins of the old mines, the miners' huts, and inscriptions to the Goddess Hathor, the Lady of the Turquoise, can be found to this day in the Sinai. Copper mining in the Sinai Peninsula continued until the reign of Ramses III, in 1150 B.C., over 2,000 years later.

With the help of copper implements, King Zoser, founder of the Third Dynasty of Egypt, built the first great pyramid, the Pyramid of Saqqara, about 2900 B.C. The Great Pyramid of Gizeh, built by King Khufu, followed 100 years later.

Copper reached the island of Crete from Egypt. A copper axe from about 3000 B.C. was found on the floor of the ruins of a house. Egyptian barges carried copper to the western coast of Asia Minor, where they traded for the famous cedar wood from what is now Lebanon. The ships then went west to Cyprus, further west to Crete, then 320 miles south back to the Nile Delta. Ruins of the great Cretan civilization hold artifacts with Egyptian influence, such as fresco painting, pottery, and stone statuettes. However, the form of the metal objects is more like that from Asia Minor.

Metallurgy from Asia Minor reached Cyprus about 2600 B.C. The peoples of Anatolia (now Turkey) migrated west on favorable sea currents in the eastern Mediterranean. The people of Crete developed an industry based on copper, giving the copper miners of Cyprus an incentive to expand their mines. Egyptians traded fabrics and gold for copper from Cyprus. Myceneans settled near the copper deposit of Skouriotissa on Cyprus. This deposit was rediscovered by Charles Gunther and mined again in modern times.

Early metalsmiths of Sumer, Babylon, and Egypt were highly prized members of their society. Often, they were not free, owing their obedience and livelihood to temple priests and authorities. They were so valuable that invading armies made a special effort to carry them off in captivity. Metalsmiths transmitted their secrets to their children. Their guilds may have been the first trade unions in history.

The Bronze Age in Sub-Saharan Africa

Digging for ancient ruins in Arica south of the Sahara Desert has been difficult due to colonialism and war. Nonetheless, a copper-using civilization existed at least 2000 years ago in southern Africa where the modern nation of Zimbabwe stands.

Egypt sought gold and antimony in the land of Punt. While the exact location of Punt is unknown, it probably was along the mouth of the Zambesi River in the area where now are the nations of Mozambique and Zimbabwe. The gold obtained there has a distinctive greenish tint, probably from impurities of copper and antimony.

The Bronze Age in Asia Minor

As we have seen, copper is a soft and malleable metal. These properties made it possible for early civilizations to discover copper and to discover how to form it into containers, tools, ornaments and weapons. However, copper is so malleable that it doe s not hold an edge for long. However, the addition of a small amount of the metal tin to the molten copper creates an alloy (a combination of metals) that is much harder and holds a better edge. This alloy is called bronze.

Tin deposits are much less common than copper deposits. None of Egypt's copper or gold deposits were near tin deposits. Thus it was that Egypt did not use bronze until the 18th Dynasty. In the land that is now the nation of Iran, there are abundant copper deposits even today. There also were associated deposits of tin. It is fortunate that the great pioneering metallurgists of the ancient world, the people of Mesopotamia, stumbled over a combination of copper and tin. The Sumerians were the first civilization to use bronze in commerce.

Early bronze varied in tin content, with other metal impurities mixed in, such as lead, zinc and antimony. The impurities, metals that often are found with copper in nature, tell us that the formula for bronze was probably a lucky discovery stemming f rom the melting of impure ore. Later experience showed that the best bronze consisted of about 90% copper and 10% tin.

In order to be successful miners and metallurgists, the Sumerians also became the world's first mineralogists. They cataloged over 150 minerals. They learned that the mineral that was t he source of tin is the mineral cassiterite, a tin oxide.

The availability of bronze spurred trade and warfare. The ancient civilizations developed partly to make it possible to get copper and to work it, in order to protect, improve, and expand their civilization. Mining and trade were needed to obtain copper and tin, armies were needed to protect the mines and t he shipments of copper and tin, markets were needed for the trade goods, and industry was needed to generate goods to trade for copper. The relative boom times of the Bronze Age are due to the steps taken to fill these needs.

Around 2350 B.C., a warrior king named Sargon I conquered the warring city-states of Sumer and united them to the kingdom of Akkad. His dynasty collapsed in civil war about 2150 B.C. The city of Babylon rose to be the most powerful state in the region, ruled by Hammurabi, in about 1900 B.C. It was succeeded by the empire of Assyria.

Troy, the city destroyed in Homer's epic story, The Iliad, also used bronze, as did its Greek (actually, Mycenaean) conquerors. Troy was situated where a river flowed into the Mediterranean . With access both to sea and land trade routes, it was an important center in the Bronze trade. Bronze continued to be the most important metal in the ancient world for about 1500 years, until weapons of iron displaced it in about 1000 B.C.

The Mycenaeans were conquered by the Acheans in 1300 B.C. The Acheans are the true Greeks of antiquity. They assimilated into Mycenean society. Competition with Troy arose over trade. Troy was only one of a series of cities built on the hill of Hissarlik. It was destroyed by the Myceneans around 1200 B.C. Homer's tale of the war, The Iliad, was not written until 800 B.C.

Late in the Bronze Age, the Phoenicians became the most important metalworkers and traders of the Mediterranean world. Their origins are shrouded in mystery. According to the Greek historian Herodotus, they were descended from immigrants from the Per sian Gulf or Babylonia around 2750 B.C. They lived in what is now Lebanon, in the great seaport city of Tyre. Their barges, rowed by slaves, carried objects of gold, silver, and bronze, colored glass and alabaster bottles filled with perfume, purple fab rics, and timbers from the Cedars of Lebanon. They settled the colony of Gadir in Spain in 1100 B.C. This colony is today the modern city of Cadiz. In Spain they helped to find tremendous deposits of gold, silver, copper, and iron. They also settled t he northwest African colony of Carthage, that became the great enemy of Rome. The Phoenicians traded and distributed tools and weapons made of the new metal, iron, and so helped to end the Bronze Age.

The Phoenicians' greatest contribution to western civilization arose from the manufacture and trade in papyrus paper in their seaport of Byblos. They developed an alphabet based on the so unds of consonants. The Greek word for book, biblion, is based on the name of the Phonecian paper manufacturing center, Byblos.

Hired by King Solomon of Israel, Phoencian craftsment built the great Temple in Jerusalem. Solomon obtained copper in the desert to the south, near the town of Eilat. Copper mines in this area were reopened by the modern state of Israel.

The Bronze Age in Europe

Bronze was brought to Europe by roving Mycenaean merchant fleets. The island of Crete was a center for the expansion of the bronze trade to Europe. With few metal deposits of its own, Crete became a crucial center of trade. In the ruins of the vibrant civilization of ancient Crete, bronze weapons, tools, mirrors, and even razors are found.

The Mycenaeans created the finest bronze weapons. Their traders reached the island of Sicily and surrounding islands. On the Italian mainland, their bronze-age culture encountered the culture moving south from the metallurgical centers along the Danube River in Central Europe. Bronze implements of Mycenaean design are found in ruins there. They reached the peninsula of Spain (also known as Iberia) about 2000 B.C. The stone-tool using population was eager for bronze tools. The merchants discovered tremendous mineral deposits in Spain, including gold, silver, iron and copper. Sailing around the Iberian peninsula, the Mycenaeans also settled in what is now Portugal.

The Danube River provides a trade route from the east into Central Europe. Bronze reached the Danube valley as early as 2400 B.C. Troy was a gateway to this trade. The Erzgebirge, or "Bronze Mountains" of Bohemia (now the Czech Republic) provided both copper and tin ores to the new civilization. The Unetician culture, near the modern city of Prague, developed a bronze industry about 1600 B.C. The Uneticians also traded in salt from Austria, amber from the Baltic, and gold from nearby deposits.

Bands of traders called the Bell-beaker Folk, after their distinctive bell-shaped pottery drinking vessels, carried bronze to the British Isles. No one knows who these traders were, but their activities intensified the ancient industrial boom of the bronze age. They spread westward through England, and their distinctive bronze knives and axes have been found in County Wicklow, Ireland.

Cornwall, on the southwest coast of England, had deposits of copper and tin. The Bell-beaker Folk may have participated in the building of Stonehenge, in the southwest tip of Cornwall. They, in turn, were replaced by newly arrived Unetician merchants and warriors. In Wessex, in southwest England, the Uneticians used British tin and copper, and Irish gold to create a glittering civilization at the end of the Age of Bronze.

The Bronze Age in Asia

Copper, then bronze, came into use at about the same time in Asia. Bronze artifacts dated at 3600 B.C. have been found in Thailand. Copper is found scattered around East Asia. Tin is found in the penninsula of Malaysia.

Chinese written records date the first copper mining at about 2600 B.C. and the first casting of copper vessels at about 2200 B.C. The Shang dynasty's capital of Anyang in northern China had a bronze-casting industry in 1400 B.C.

A few traces of a bronze industry from before 2000 B.C. are found in India. However, the great use of bronze in India came after the Age of Bronze, when it became a medium for religious sculpture. The bronze sculptures of Gandhara in the 1st century, A.D., begin the continuous history of Indian bronze. Other Asian cultures were influenced by Indian art, especially in Sri Lanka, Cambodia, and Thailand.

Importance of the Bronze Age

The Bronze Age lasted from about 2500 B.C. to about 1000 B.C. In 1500 years, human beings had developed trade, metallurgy and mining. They had learned how to seek and use natural resources. They created institutions to protect and to expand their trade and industry. The entire Eastern Hemisphere was changed forever. The foundation stones for modern civilization were laid.

Copper From the Bronze Age to the Fall of Rome

Replaced by iron for weapons and tools, copper and bronze became metals used in architecture, art, and certain specialized uses such as copper pots. The alloy brass, in which copper is mixed with zinc, was discovered sometime before 600 B.C.

The state of Lydia, south of Troy in western Turkey, invented the idea of coins as a medium of exchange. Coins were small and portable, had a set value, and were more convenient for trade than the bulky system of barter. Gold, silver, copper, and bronze were used for coins, a use that continues today in our penny. Greek coins with the head of an owl on the back, known as "Owl Coins", were the most important medium of exchange in the 5th century B.C. Thus, the idea of money was born.

The Etruscans reached the glorious days of their civilization about 800 B.C., before the rise of Rome. They were descendents of immigrants from Lydia. In the mountains of the modern Italian province of Tuscany, the ancient Etruscans found copper and tin ores. Iron ore was conceniently near on the Island of Elba. While they created superb iron weapons, they produced magnificent statues in bronze. Joining the Phoenicians in seafaring trade, the Etruscans were rivals of Greek traders around the Mediterranean Sea. Caught between Gaulic invasions from the north and the rising Roman city-state to the south, the last Etruscan city yielded to Rome in 396 B.C.

Rome explored all around the Mediterranean for mineral wealth to support its growing empire. The Romans also acquired immense Phoenecian mineral wealth when they destroyed the Phoenecian colony of Carthage. This wealth included the great metal mines of Spain. A huge copper deposit was found in the soutwest corner of Spain. Copper and iron on the surface of the Earth at that deposit colored a nearby river red. It is thus called Rio Tinto. The mining district was named Rio Tinto as well. The deposit originally consisted of a reddish mountain, with iron, silver and gold as well as copper. 3000 years of mining have left a crater where the red mountain once stood. The crater is over 800 feet deep and over three-quarters of a mile wide. In the walls, one can see remnants of Roman tunnels and shafts. Water wheels with bronze axles used to lift water out of the ancient tunnels are still found. Slaves ran the water wheels by walking on treadmills.

Mining techniques had changed little. Besides using fires to crack rock, quicklime was stuffed in cracks, then wetted with water. As it became wet, the quicklime expanded, breaking off chunks of rock.

To allow miners to carry ore to the surface, spiral stairways were cut in the rock around the sides of shafts. Where the space was too cramped for stairs, notched poles were used as ladders. Up to 200 hundred pounds were carried by each worker, in leather buckets on their backs.

The deep mine workings tended to fill with water despite the water wheels. A drainage tunnel over a mile long and reaching a thousand feet deep was dug to join up with the mines.

In the early days of the Roman empire, conquests of new lands were being made at a great rate. As a result, many prisoners of war were carried to Spain as slaves. Because slaves were plentiful, conditions were horrible for workers in the mines. Later in the Roman empire, when new slaves were less easy to obtain, slaves became more valuable. Roman labor laws were passed that mandated working conditions for the slaves in the mines. Tunnels and shafts had to be supported adequately with timbers, in order to prevent collapse. Miners were entitled to sleeping and bathing accommodations, food, and specific hours of work. These labor laws were more humane than many miners faced in the early 20th century!

Rio Tinto is still being mined today. Now the miners are working in open pits, rather than the tunnels of the ancient Romans. Millions of tons of black slag remain from Roman smelting operations. The slag contains small amounts of gold and silver, as well as copper, showing that the Romans were interested in these precious metals.

Miners today are mining brassy yellow copper "sulfide" minerals such as chalcopyrite. The sulfides were more difficult to smelt than the green and blue copper "oxide" minerals used by the Sumerians. The Romans were fortunate that the oxide ore was closer to the surface, and that there was a great deal of it.

The Romans did find a way to use the sulfide ores, although the process was very slow and probably produced little copper. They collected water that seeped through the mines. Copper dyed the water blue. The sulfur in the minerals turned into a combination of oxygen and sulfur called "sulfate". Sulfate in water makes sulfuric acid. This blue water was called chalcanthus by the Romans. When dried to make a copper sulfate mineral of the same light blue, that mineral is called chalcanthite. The Roman Empire's expansion and wealth depended on mines outside of the boundaries of the original Roman city state. Exploration for new mineral wealth was often the motive for Roman military expansion. Julius Caesar, for example, sought to increase his personal fortune by controlling the tin deposits of Cornwall, when he invaded Great Britain.

During most of the time up to the Roman empire, sufficient copper ore was available to meet the needs of the Mediterranean world's demands. However, the ore of Rio Tinto that could be exploited by Roman technology was exhausted by the fall of the Roman Empire. Rio Tinto became a ghost town. Barbarian invasions of the Fifth Century A.D. pushed Europe into the Dark Ages. Europe became a chaotic and dangerous place. Mining and metallurgy, like the rest of European culture, froze in place for centuries.

In order to smelt "sulfide" minerals, that is minerals made of copper, iron, lead and zinc chemically bound to sulfur, they have to be heated and "oxidized" first. The more easily smelted ores were exhausted by the time of the fall of Rome. The Moors lived in southern Spain during the Middle Ages. They used copper for cooking utensils and for ornaments. To continue to mine the still vast sulfide ore deposits of Rio Tinto, they developed a new process. They collected the ore, broke it into pieces, and piled it into heaps. Water was allowed to seep down through the heaps. The water was then collected. This technique is called "heap leach." The resulting solution contained copper in the form of copper sulfate. There was far more copper in the water than in the mine water collected by the Romans. Iron was placed into the water containing copper sulfate. A reaction occurred, in which the iron dissolved into the water, and copper precipitated where the iron had been.

With iron being used for most weapons and tools, Rio Tinto was able to keep up with Moors' copper needs. However, the Spanish under King Ferdinand and Queen Isabella drove the Moors out of Spain in 1492. Interested in mines in the New World, the Spanish ignored the Rio Tinto district. However, other Europeans found that Rio Tinto was still richer than any mine in their district. The Spanish government leased the mine to a succession of Europeans.

In 1873, the London firm of Matheson and Company bought the mines. The new prosperity of Rio Tinto was brought about by a great new innovation in smelting sulfide ore. Heap leaching is very slow. It may take years to get enough copper sulfate solution. However, miners discovered that if the ore was burned or roasted before leaching, as much copper could be collected in 6 months as in 3 years with unroasted ore.

There were drawbacks to the new process, however. Roasting the sulfide ore released hydrogen dioxide gas. Clouds of this gas choked the miners and smelter workers and killed all the vegetation around Rio Tinto for up to 15 miles. This same problem has occurred around other copper smelters.

It was discovered, however, that the sulfur was also a valuable commodity. Now the sulfur is collected, to be sold to other industries to make sulfuric acid. Sulfuric acid is one of the most useful and important chemicals in the world.

Copper in the Middle Ages and Renaissance

A good picture of copper mining, metallurgy, and use in the Middle Ages and Renaissance can be obtained from De Re Metallica, by Georgius Argicola, published in 1556. An excellent translation was prepared by Herbert Hoover (a mining engineer and later Pre sident of the United States) and his wife, Lou Henry Hoover (the first woman geologist to graduate from Stanford University).

De Re Metallica is illustrated with woodcuts that are widely reproduced in modern books. Since metal work and mining had been performed by people with guild secrets to keep, and little interest in writing books, Agricola was one of the first people in history to record mining and metallurgical practices. He lived in the silver mining region around Freiburg, Germany. His observations were achieved through personal observation.

Agricola gave detailed descriptions of mining techniques and equipment, mine surveying, mining law, mining industrial organization, copper minerals, vein deposits and ways to recognize them, assay techniques to determine the amount of copper contained in an ore rock, ways to smelt copper into cakes, and to purify it.

It is apparent reading his work that mining had progressed only slightly from the days of the Romans. Without explosives, rocks were still plucked from shafts and tunnels with picks and shovels. Tunnels were supported with timber (they are still), an d miners and ore were raised and lowered using winches. Techniques existed to drain water away from deep shafts, and to blow fresh air into them.

Another pioneering author of a book on metals and metallurgy lived about the same time as Agricola. Vanoccio Biringuccio, of Sienna in Italy, published the Pirotechnica in 1540.

Agricola mentions Biringuccio in De Re Metallica. Pirotechnia was published in the Italian language, unlike Agricola's Latin text. Like Agricola, Biringuccio illustrated his book with woodcut drawings.

After Rome fell to Barbarian invasions in 410 A.D. and again in 455 A.D., Europe was plunged into a time of war and uncertainty. Skills were forgotten. Trade stopped. Mining, except for iron for weapons and tools, was nearly abandoned. This period is called the Dark Ages.

Clovis, the chief of a tribe of Franks, created a state near Paris extending to the Rhine near Strasbourg in 486. His descendant, Charlemagne, was crowned Emperor of the Romans in the year 800. He expanded his kingdom into the old metal district in t he Erzgebirge Mountains of central Europe. Silver was mined by captive Saxons to become the new coins of his empire. Mining was beginning to revive in Europe.

In Germany, in the Kingdom of Otto, in 938, a German nobleman was riding his horse, Ramelus. The nobleman was hunting near the town of Goslar in the Harz Mountains. He tied the reins to a tree when he dismounted to hunt. Ramelus was impatient and pa wed the earth. When the nobleman returned, he saw metals gleaming in the horse's little excavation. Miners realized that the horse had uncovered a vein of silver, lead, and copper. This mine was named Rammelsberg, after the horse Ramelus.

Rammelsberg became the most important source of silver, lead and copper in central Europe. Over a thousand years later, it still produces wealth. Like the gold rush in the United States, it inspired German expansion to the east, to search for more mi neral deposits. It also trained miners in the skills lost to the Dark Ages, in mining and prospecting.

During the Middle Ages, many common people belonged to the land and to the lord of the land. They were not free to leave. However, the lords began to need money to buy luxuries from the Near East and China such as silk. These new ideas and luxuries c ame from European contact with Moslems during the Crusades. From the First Crusade in 1096, kings and princes needed money for luxuries and to pay for more armies to wage more Crusades. They allowed adventurous serfs their freedom to look for ore deposi ts. A freed serf who found a deposit could mark the boundaries of the deposit with piles of stone. Then he could apply to the lord who owned the land for permission to mine the deposit. The lord, in return, was granted tribute or a royalty. This pract ice is very similar to modern claim staking on public land. Medieval miners became respected craftsmen, not serfs.

Two hundred miles southeast of Rammelsberg, in the foothills of the Erzgebirge or "Ore Mountains" of Bohemia, another great deposit was found in 1170. Silver thalers or coins were minted in Joachimsthal, now known as Jachymov in the Czech Republic. T he word "dollar", first applied by the United States to silver coins, comes from thaler. In the same area, copper and tin deposits provided the metals for the bronze bells, statues and doors of the great gothic cathedrals of Europe.

The same craftsmen that cast the cathedral bells cast the first bronze cannons. Using cannons in the Hundred Years War, the British won their first victory over the French in 1346 at Crecy.

The demands of these new industries drove miners to follow their deposits deeper into the Earth. Old mining methods were no longer sufficient. European miners borrowed the idea of using water wheels from the Moors and Chinese. Formerly, water wheels were used to grind corn. Now, the late Medieval miners used them to pump water from the mines, grind ore, run bellows at the blast furnace, and operate hammers at the metalsmith's forge. The idea of using machinery was applied quickly to other industries such as cloth making and lumber.

Mining had become a very expensive industry to operate. Capital, that is, money, was needed to find, develop, and run a mine. Miners often were employees. The Fugger family financed copper smelters. They used the resulting fortune to finance and su pport the Austrian Hapsburg dynasty of emperors. Great banks and banking families arose in Europe.

The result of mining in central Europe was to bring wealth and power to the German and Austrian princes and emperors of the region. German technical know-how became important in the subsequent history of Europe.

The first explosives to crack rocks in a mine probably were used in the Hungarian Erzgebirge in 1627. There, the holes that had been drilled in the rock were packed with black powder.

Steam engines first pumped water out of mines in England, in Cornwall in 1711. Thomas Newcomen invented the steam-powered pump. James Watt improved it. While tin was the most valuable metal mined in Cornwall, copper also was found in the mines. Two mines alone produced twenty million dollars worth of tin and copper. Mining continues in Cornwall today, although far less than during the Nineteenth Century. But the invention of a steam -powered machine to assist in mining brought about the Industrial Revolution, and the modern world as we know it.

The miners of Cornwall took their knowledge of deep, hard rock mines with them to the New World. They helped to develop the great mining districts of the Western United States.

Copper in the Western Hemisphere

The Native Americans of South America used copper tools and weapons long before the European invasion of their land. As early as 700 A.D., the Chimu of coastal Peru were making bronze. They influenced neighboring cultures in Ecuador and central Peru.

The Inca Empire of Peru was near to the great copper and tin deposits of Bolivia. While copper was used for spears and axes, bronze implements were beginning to appear at the time of the invasion by Francisco Pizarro and the Spanish Conquistadors. Magnificent works of art in gold and silver attracted the Spanish to Inca land. Alas, most of the treasure was melted down and shipped to Spain. Gold, silver and copper mining continues to this day in Peru. Copper and tin are still mined in Bolivia.

Native American copper mines have been found in Michigan's Upper Peninsula, along the southern shore of Lake Superior. Spearheads and other hammered copper implements have been found there as well. The great purity of the copper nuggets in Michigan made other types of metallurgy unnecessary. The pure, malleable copper needed only to be beaten into the desired shape.

Mexico and Central America were home for other great Native American civilizations. The Aztecs of Mexico were master goldsmiths and silversmiths. Mexico, too, was a vast storehouse of mineral wealth. They had hammered copper implements when conquered by Hernando Cortes and his Conquistadors in 1521.

In northern Mexico, in the Sierra Madre Occidental mountain range, copper deposits were found. There, the Cananea and Nacozari mines made up one of the world's great copper districts.

Chile, today, is the world's largest copper producer. However, the great Chilean copper mines are of a type first exploited in the United States, at Bingham Canyon, in Utah. But more of that below...

Copper Mining in the United States

In the United States copper was mined and worked in 1709 in Simsbury, Connecticut. Westward expansion of European settlement expanded the copper industry as well. The copper deposits of Michigan's Upper Peninsula were mined starting in the 1850's near Native American copper workings. Two companies, Calumet and Hecla, developed the mines guided by copper nuggets and outcrops found on the surface. Calumet was named after a Native American peace pipe.

The Butte, Montana, copper vein deposits were worked starting in 1866, adjacent to placer gold mines. The Butte deposits, later called "the richest hill on earth," became the chief copper supplier for the nation by 1886. The principal company in Butte was Anaconda, controlled by Marcus Daly, an Irish immigrant who had learned about mining in the Comstock District of Nevada. The veins were silver-rich at the surface, but as Daly predicted, they became rich in copper deeper in the earth. Anaconda Mining Company dominated world copper production for a while. Daly's rival in Butte was W. A. Clark, who used his mining expertise to gain wealth and political power.

As the Industrial Revolution intensified in the 19th Century, new uses for copper were developed. New sources of copper were developed as well. Copper wire is vital in the use of electricity. The telegraph was patented by Samuel F. B. Morese in 1840. The telephone was demonstrated by Alexander Graham Bell in 1875. Thomas Edison applied for a patent on the incandescent lamp in 1879. A blue and green copper mineral deposit near Santa Rita, New Mexico, had been mined by Native Americans for dyes and pigments. Mexicans took native copper from it in 1804 and carried it on pack mules all the way to Mexico City to be used in coins.

In 1854, surface outcrops of copper in the Papago Indian country were mined by Colonel Charles D. Poston. Copper ore was carried in ox carts from the mine at Ajo to the Colorado River at Yuma. The ore was carried on barges on the Colorado to the sea, then to a smelter overseas.

Arizona became a territory of the United States in 1863, due to its richness in metals. The mountain stained blue and green by copper in the Clifton-Morenci district was discovered by soldiers in 1871. The mountain, near Superstition Mountain next to Superior, Arizona, became the Silver Queen Mine belonging to Magma Copper Company.

At Mule Canyon, south of Tombstone, Arizona, in 1877, a soldier chasing Apache Indians found copper at Bisbee. The Copper Queen Mine and neighboring Atlanta Claim became the fabulous Warren District. With the great contribution of the Warren District, Arizona lead the nation and still leads it in copper production.

Overlooking the Verde River, the United Verde copper mine at Jerome, Arizona, was financed by eastern capitalists. The Jerome family included the mother of British Prime Minister Winston Churchill. However, the rich surface ore soon played out. W. A. Clark, who had obtained his fortune at Butte, purchased 99% of the stock of the United Verde Mine. Ultimately it yielded copper, silver, and gold totaling $410,000,000. W. A. Clark was the owner of the richest, individually owned copper mine in the world!

Soldiers found gold nuggets in Bingham Canyon in Utah, near Salt Lake City, in 1862. By 1870, 2 million dollars had been mined in gold. In 1873, silver-lead veins were discovered in the canyon walls. The Highland Boy was one of the several mines begun to exploit these veins. It discovered ore that ran 15% copper. The first copper was shipped in 1896. The Highland Boy and nearby claims were acquired by the Utah Consolidated Copper Company in 1899. An experienced miner, Enos A. Wall, observed blue and green colors above the mine in the canyon walls. The copper had been tested and made up only 2.4% of the rock, or 48 pounds of copper per ton of rock. This amount was believed to be too small for a profitable mine. However, Wall realized that the low-grade deposit in the mountain above the canyon was enormous. He bought up 200 acres. Then he hired two young mining engineers, Robert C. Gemmel and Daniel C. Jackling. They tested the mountain and reported evidence of over 12 thousand tons of ore, with a probably 25 million more tons. Since it was low grade, that is, there was a low proportion of copper in the rock, it would have to be mined with new methods. Jackling suggested a new mining technique, in large open pits, using huge mechanical shovels and ore cars in trains to carry the ore to the mill. Wall became a director of the new Utah Copper Company. In 10 years, the new company mined 67 million tons of ore with 1.4% copper. The mine was named Bingham Canyon. It continues to produce copper from one of the largest human-made pits on earth.

This new type of copper ore was found in a type of rock called a "porphyry", a sort of granite with a fine-grained groundmass with large crystals embedded in it. The copper minerals are spread thinly but evenly through the porphyritic rock, in a style of mineralization called "disseminated." Accordingly, similar deposits were called "Porphyry Coppers." Prospectors went looking for more Porphyry deposits, and found them at Santa Rita, New Mexico, Miami and Morenci, Arizona, Ely and Yerington, Nevada, and in several places in Chile.

Kennecott Copper Corporation got its start in a deposit under glaciers on a peak in the Wrangell Mountains of Alaska. Gold prospectors passed the copper on the way to the Klondike, but did not see it. Finally someone noticed an outcrop of the black copper sulfide mineral, chalcocite, in 1906. This rich deposit became the Jumbo Mine. It produced two hundred million dollars in copper and gold.

The story of Nevada's great copper deposits will be told below. We will explore the history of the deposits of Ely, Yerington, Mountain City, and Battle Mountain.

As you have seen, the history of copper mining and metal working is the history of civilization. Mining led to advances in civilization from technology to trade, to art, and to warfare. People developed their civilization to develop mining that allowed their culture to further evolve. Now, we can consider the modern copper industry.

The Modern Copper Industry

Copper Uses Today

Copper is a critical component of modern industry. In the United States, the most important use of copper is in electrical wiring. A breakdown below gives the percentage of copper used in the United States by industry:

Building Wire . . . . . . . . . . . . . . . . . . . . 16%
Plumbing & Heating. . . . . . . . . . . . . . . . . . 14%
Automotive. . . . . . . . . . . . . . . . . . . . . . 11%
Electric Utilities. . . . . . . . . . . . . . . . . . .9%
Air Conditioning & Commercial Refrigeration . . . . . .8%
Telecommunications. . . . . . . . . . . . . . . . . . .7%
Factory Equipment . . . . . . . . . . . . . . . . . . .6%
Electronics . . . . . . . . . . . . . . . . . . . . . .6%
Appliances & Extension Cords. . . . . . . . . . . . . .3%
Other . . . . . . . . . . . . . . . . . . . . . . . . 20%
TOTAL ---------------------------------------------> 100%

Copper sheets are used in cooking utensils and in roofs. Copper tubes are used to make pipes for plumbing and carrying natural gas. Copper wire is used to carry electric current. Extruded copper, that is, copper that has been squeezed through a hole, forms rods, hinges, tubes, and door handles.

The use of copper is increasing. In the 1970s, a 1,500 square-foot house used about 280 pounds of copper. Today, a 2,200 square-foot house uses about 450 pounds of copper.

A car in the 1970s used about 35 pounds of copper. Now, 50 to 80 pounds of copper will go into one automobile.

A Boeing 727 airplane uses 9,000 pounds of copper.

Where is Copper Mined?

The following countries are the world's major producers of copper
(amount produced is 1995 output, given in tons, from the 1995 Mineral Commodity Summary)

Chile  . . . . . . . . . . . . . . . . . . . . 2,350,000
United States of America . . . . . . . . . . . 1,890,000
Canada . . . . . . . . . . . . . . . . . . . . . 740,000
Russia . . . . . . . . . . . . . . . . . . . . . 600,000
Indonesia. . . . . . . . . . . . . . . . . . . . 380,000
Australia. . . . . . . . . . . . . . . . . . . . 420,000
Peru . . . . . . . . . . . . . . . . . . . . . . 400,000
China. . . . . . . . . . . . . . . . . . . . . . 350,000
Zambia . . . . . . . . . . . . . . . . . . . . . 350,000
Poland . . . . . . . . . . . . . . . . . . . . . 340,000
Kazakstan. . . . . . . . . . . . . . . . . . . . 220,000
Philippines. . . . . . . . . . . . . . . . . . . 115,000
Zaire. . . . . . . . . . . . . . . . . . . . . . .40,000
Other Countries. . . . . . . . . . . . . . . . 1,600,000
WORLD TOTAL----------------------------------> 9,800,000

While the U.S. is the world's second-largest producer of copper, it is the world's largest consumer of copper. The United States imports 830,000 tons of copper. It also exports 850,000 tons.

The largest mining companies are Codelco and Minera Escondida of Chile (of which 57.5% is owned by BHP of Australia), and Phelps Dodge in the United States, followed by RTZ, Asarco, Freeport, ZCCM, Cyprus, and MIM.

In the United States, Arizona is by far the largest producer of copper, followed by Utah and New Mexico. Montana has been the fourth largest producing state, but the opening of BHP's Robinson Project in Ely, Nevada, will move Nevada into fourth place ahead of Montana. Michigan followed Montana, but the largest of the few remaining mines in Michigan has closed. Historic mines or mining districts discussed in the preceding section are still producing in these states, especially Bingham Canyon in Utah, Ely, Nevada, and Butte, Montana.

Used copper can be recycled by resmelting it. Last year, 460,000 tons of copper, or 18% of U.S. copper use, was recycled.

INTERNATIONAL TRADE IN COPPER

Copper is traded around the world. Producers store it in warehouses until it is sold and shipped to the buyer. The price changes daily, depending on the supply of copper and the demand for copper. The principal place where the trading takes place is in London, at the London Metal Exchange. There, copper sellers try to find a buyer who will pay the highest price for shipment at a certain time, while buyers look for the lowest priced copper. The average price per pound has fallen in 1995, going from a high of $1.37 per pound to around $.91 per pound.

Other metals can substitute for copper in some uses. For example, aluminum may be used in electrical equipment, automobile radiators and refrigerator tubing. Titanium and steel are used in heat exchangers. Steel is used for artillery shell casings. Plastics substitute for copper in water pipe and plumbing fixtures.

Mining and Metal Extraction

MINING

Most modern copper mining is done in open pits with explosives, giant shovels, and huge trucks to haul the ore to a mill or smelter.

The method of extracting copper from ore rock has been improved with modern technology, but the ideas behind it developed directly from past experience. Since every ore is at least a little different from every other ore, the exact process varies with the type of ore. Sometimes the copper ore mineral is different; for example, chalcocite (copper sulfide) is very different from malachite (copper carbonate with water). The non-copper minerals in the ore, called gangue, vary as well.

TRANSPORTATION AND CRUSHING

In most cases, the mined ore must first be carried to a mill. Still in large boulder-sized pieces, it is transported in trucks, in railroad cars or in a pipeline. It is brought to a crusher, where it is crushed into small pieces.

The small pieces are mixed with water until they form a chunky soup called slurry. The slurry is poured into a ball mill. A ball mill is a barrel-shaped container that rotates while holding steel balls that clash together to grind the ore into tiny pieces. These pieces are small enough to pass through a screen with 10,000 openings per square inch.

The next step is a flotation process, where soap-like bubbles hold the tiny particles of copper minerals, while the unwanted parts of the ore sink into the liquid. The slurry is placed in a flotation cell. Chemicals are added to coat the copper particles and to make the bubbles stronger. Then paddles or air jets make the whole thing bubble. The bubbles containing the copper rise to the top of the liquid where they can be skimmed off. The unwanted parts, now called tailings, sink to the bottom to be poured off. The froth containing the copper is dried, and the product is called copper concentrate. It contains about 15 to 33 percent copper.

Sometimes part of the copper ore, or even all of it, does not separate out in the flotation cell. Then another process named leaching is used. As we learned previously, this process was discovered by the Romans. They could not smelt the sulfide copper ores (ore made of the minerals chalcocite, chalcopyrite, bornite, and other minerals in which copper is bonded to sulfur). The Romans collected water from deep in the mines that had seeped through the sulfide ore. They let the water dry, and collected the copper minerals from it. We also saw that the Moors figured out how to pile the sulfide copper ore in heaps and drip acidic water through the heaps, then smelt the results. This process was the first use of heap leaching.

Nowadays, after leaching has removed the copper from the ore and dissolved it into a sulfuric acid-water solution, the solution is placed in containers holding pieces of iron. Some of the iron dissolves and replaces the copper in the solution. The copper, meanwhile, is deposited on the remaining pieces of iron. The resulting copper concentrate is called precipitate copper and is from 60 to 90 percent pure copper. From this point, usually it must be smelted or refined to remove the rest of the impurities.

Smelting, too, is an ancient process made more efficient and precise through modern technology. The typical furnace now used is called a reverberatory furnace. A large amount of concentrate, up over 300 tons, may be placed in the furnace at one time. The flames from one end of the furnace melt the concentrate. Bubbles rise to the surface releasing some impurities in the form of gas. Other impurities form a less dense liquid, like salad oil floating on top of vinegar, that rises to the top of the copper melt. These impurities include iron, calcium oxide (a mixture known as lime), and silicon and oxygen (a mixture known as silica). The impurities are called slag. The slag is skimmed off the top. The melted material is now a mixture of impurities and up to 50 percent copper. It is called copper matte. The remaining impurities include iron and sulfur.

The copper matte goes through a converter to blow forced air into it. The air forces silica back into the copper matte to gather up the impurities and make more slag. The slag is skimmed off again. Now, the matte is up to 99.5 percent pure copper. It has a bubbly surface and so is known as blister copper.

For use in electrical wire and instruments, copper must be even more pure. A technique that the ancient copper smelters and the medieval smelters, and even the Renaissance smelters could not use, is electrolytic refining. The blister copper is poured into molds to make cakes about 3 feet on a side and about 3 inches thick. These cakes will form positive poles called anodes.

The copper anodes are lowered into tanks containing a solution containing more copper in the form of copper sulfate, and nitric acid. They are arranged so that hanging between them are sheets of pure copper that will be the cathodes or negative poles. An electric current is passed through the tank. The anode copper cakes dissolve. Impurities sink to the bottom as sludge. Pure copper deposits on the cathode sheets. These pure copper sheets can be remelted and cast into whatever form is needed.

Properties of Copper

Atomic Properties

As we saw at the beginning of this article, copper is Atomic Number 29, that is, an atom of copper has 29 protons. The Atomic Weight is 63.54. The Atomic Symbol is Cu.

Copper is in column IB of the Periodic Table of the Elements, above Silver (Ag) and Gold (Au). Elements in the same column have some similar properties. Like silver and gold, copper is soft (with a Moh's hardness of 2.5 to 3, that is, harder than a fingernail, but softer than a steel pocketknife). The surface has a metallic luster. With a specific gravity of 8.2 (based on the density of 8.2 grams per cubic centimeters, g/cm3), it is far denser than water with a specific gravity of 1, or sulfur, with a specific gravity of just over 2, or carbon in the mineral graphite (2.23). Silver, however, is below copper in column IB, and so it is denser (10.5) and gold, even lower, is far denser at 19.

When Copper combines with other elements, it has a charge of either +1 (called "cuprous") or +2 (called "cupric").

Physical Properties

Like gold and silver, copper is malleable. That is, it can be bent and shaped without cracking, when either hot or cold. It can be rolled into sheets as thin as 1/500 of an inch.

Copper also is ductile, that is, it can be drawn out into thin wire. A copper bar 4 inches thick can be heated, rolled, then drawn into a round wire so thin that it is thinner than a human hair. This wire is 20 million times longer than the original bar!

Industry valued copper for these properties. Copper is second only to silver in its ability to conduct elecricity, but silver is too expensive for this sort of use. Bronze and brass, however, do not conduct electricity as well as pure copper.

Besides electricity, copper also is an excellent conductor of heat, making it an important metal in cookware, refrigerators, and radiators.

Copper is resistant to corrosion, that is, it will not rust. If the air around it often is damp, it will change from its usual reddish orange color to reddish-brown. Eventually, it is coated with a green film called a "patina" that stops all further corrosion.

The melting point of copper is 1083.4 degrees Centigrade. Liquid copper boils at 2567 degrees Centigrade.

Conclusion

As the world moves into the new millenium, the need for copper is growing, rather than shrinking. Computers, like other electronics, require copper. As it was at the dawn of civilization, copper will continue to be crucial to the world's economy.

References

Copper References

Agricola, Georgius, 1556, De Re Metallica, Hoover, Herbert Clark, and Hoover, Lou Henry, translators, 1950. New York: Dover, 638 p.

Bass, Thomas A., 1991, Land of bronze: Discover, v. 12 (Dec.), p. 62-66.

Biringuccio, Vannoccio, 1540, The Pirotechnia of Vannoccio Biringuccio, Smith, Cyril Stanley and Gnudi, Martha Teach, translators, 1990, reprint of 1959 edition published by the American Institute of of Mining and Metallurgical Engineers. New York: Dover, 477 p.

Block, Sandra, 1996, Copper prices still on shaky ground: USA Today, June 17, 1996, p. 1B.

Brokaw, A. L., Baurer, H. L., and Breitrick, R. A., 1973, Geologic Map of the Ruth Quadrangle, White Pine County, Nevada: U.S. Geological Survey, Geologic Quadrangle Map GQ-1085, 1:24,000.

Butts, Allison, ed., 1954, Copper: The Science and Technology of the Metal, Its Alloys and Compounds. American Chemical Society Monograph Series. New York: Reinhold, 936 p.

Encyclopedia Americana. Danbury, Connecticut: Grolier, Inc., 1993.

Hose, Richard K., Blake, M. C., Jr., and Smith, Roscoe M. 1976, Geology and Mineral Resources of White Pine County, Nevada: Nevada Bureau of Mines and Geology, Bulletin 85.

Joralemon, Ira B., 1934, Romantic Copper. New York: Appleton- Century, 294 p.

Kadlec, Daniel, 1996, Regulation is weakest link in metals markets: USA Today, Monday, June 17, 1996, p. B4.

Mikesell, Raymond F., 1979, The World Copper Industry. Baltimore, Maryland: The Johns Hopkins University Press, 392.

Milliken, Frank R., 1982, Copper: World Book Encyclopedia, v.4, p. 822-826.

Motta, Mary, and Mangum, Jeff, 1996, Copper traders speculate on metal's prices: USA Today, June 17, 1996, p. 4B.

Mullins, Marcy E., 1996, Copper plunges: USA Today, June 17, 1996, p. 4B.

Ross, John R, 1975, Stones of Destiny. Houghton, Michigan: Michigan Technological University, 253 p.

Smith, B. Webster, 1967, The World's Great Copper Mines. London: Hutchinson, 117 p.

Wark, Tammi, 1996, Copper: Wired into our lives: USA Today, June 17, 1996, p. 4B.

Weiner, Paul, 1993, Copper: Encylopedia Americana, v. 7, p. 759-766.

Wilson, A. J., 1994, The Living Rock. Cambridge, England: Woodhead Publishing Limited.

The World Book Encyclopedia. Chicago: World Book-Childcraft International, 1982.

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Last Modified May 20, 1997
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The Modern Copper Industry Copper Uses Today