Sand

Sand

Sand isn’t a boring material if you know what you are looking at!

highly rounded sand from the Gobi Desert

Highly rounded sand grains from the Gobi Desert of Mongolia. Wind-blown sand sustains repeated tiny impacts as it bounces along Earth’s surface. These impacts gradually abrade sharp protrusions from the grains and give their surface a “frosted” luster. The width of this view is approximately 10 millimeters. Photograph by Siim Sepp, used here under a Creative Commons License.

 

Thinking About Sand

Sand is a common material found on beaches, deserts, stream banks and other landscapes worldwide. In the mind of most people, sand is a white or tan, fine-grained, granular material. However, sand is much more diverse – even beyond the pink sand beaches of Bermuda or the black sand beaches of Hawaii. These are just a few of the many types of sand.

What is Sand?

The word “sand” is actually used for a “particle size” rather than for a “material.” Sand is a loose, granular material with particles that range in size between 1/16 millimeter and 2 millimeters in diameter. It can be composed of mineral material such as quartz,orthoclase or gypsum; organic material such as mollusk shells, coral fragments or radiolarian tests; or rock fragments such asbasalt, pumice or chert. Where sand accumulates in large quantities, it can be lithified into a sedimentary rock known assandstone.

“Sand Size” Illustration

sand size

This photograph illustrates the size range of sand. The small tan sand grains in this photo are of a fine-grained sand from Qafsah, Tunisia. They are about 1/16 millimeter in diameter – the lower limit for a grain to be called “sand size.” The large brown grain is from near Worthing, England. It is a grain of coarse sand about 2 millimeters in diameter – the upper limit for a grain to be called “sand size.” Although sand particles are all tiny in size, there is an enormous relative size range between the smallest and largest. Public domain photo by Renee1137.

Most sands form when rock materials are broken down by weathering and transported by a stream to their place of deposition. A few types form when the shell or skeletal materials of organisms are broken up and transported. A few rare sands are formed chemically from materials dissolved or suspended in sea water.

Unusual Types of Sand

This page shows photos of a few types of sand that can be found worldwide. Most of the examples here are not typical. They are unusual types of sand that might only be found in a few locations worldwide. These unusual sands are a product of the types of material from which they are derived, the methods used to transport them, the chemical environment of their deposition site, and numerous other factors. After examining these photos you will probably conclude that sand can be a very diverse and interesting material.

Thanks to the many photographers who shared their photos through a Creative Commons License. Please see an attribution in the caption of each photo. A person would have to travel the world to get a collection of photos like this.

REE – Rare Earth Elements and their Uses

REE – Rare Earth Elements and their Uses

The demand for rare earth elements has grown rapidly, but their occurrence in minable deposits is limited.

Rare Earth Element Production

This chart shows a history of rare earth element production, in metric tons of rare earth oxide equivalent, between 1950 and 2015. It clearly shows the United States’ entry into the market in the mid-1960s when color television exploded demand. When China began selling rare earths at very low prices in the late-1980s and early-1990s, mines in the United States were forced to close because they could no longer make a profit. When China cut exports in 2010, rare earth prices skyrocketed. That motivated new production in the United States, Australia, Russia, Thailand, Malaysia, and other countries.

 

What Are Rare Earth Elements (REEs)?

Rare earth elements are a group of seventeen chemical elements that occur together in the periodic table (see image at right). The group consists of yttrium and the 15 lanthanide elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). Scandium is found in most rare earth element deposits and is sometimes classified as a rare earth element. The International Union of Pure and Applied Chemistry includes scandium in their rare earth element definition.

The rare earth elements are all metals, and the group is often referred to as the “rare earth metals.” These metals have many similar properties and that often causes them to be found together in geologic deposits. They are also referred to as “rare earth oxides” because many of them are typically sold as oxide compounds.

Uses of Rare Earth Elements

Rare earth metals and alloys that contain them are used in many devices that people use every day such as computer memory, DVDs, rechargeable batteries, cell phones, catalytic converters, magnets, fluorescent lighting and much more.

During the past twenty years, there has been an explosion in demand for many items that require rare earth metals. Twenty years ago there were very few cell phones in use, but the number has risen to over 7 billion in use today. The use of rare earth elements in computers has grown almost as fast as cell phones.

United States Usage
(2015 data from USGS)
Chemical Catalysts
60%
Metallurgy & Alloys
10%
Ceramics and Glass Making
10%
Glass Polishing
10%
Other
10%

Many rechargeable batteries are made with rare earth compounds. Demand for the batteries is being driven by demand for portable electronic devices such as cell phones, readers, portable computers, and cameras.

Several pounds of rare earth compounds are in batteries that power every electric vehicle and hybrid-electric vehicle. As concerns for energy independence, climate change and other issues drive the sale of electric and hybrid vehicles, the demand for batteries made with rare earth compounds will climb even faster.

Rare earths are used as catalysts, phosphors, and polishing compounds. These are used for air pollution control, illuminated screens on electronic devices, and the polishing of optical-quality glass. All of these products are expected to experience rising demand.

Other substances can be substituted for rare earth elements in their most important uses; however, these substitutes are usually less effective and costly.

From the 1950s until the early 2000s, cerium oxide was a very popular lapidary polish. It was inexpensive and very effective. The recent price increases have almost eliminated the use of cerium oxide in rock tumbling and the lapidary arts. Other types of polish, such as aluminum and titanium oxide, are now used in its place.

Critical Defense Uses

Rare earth elements play an essential role in our national defense. The military uses night-vision goggles, precision-guided weapons, communications equipment, GPS equipment, batteries and other defense electronics. These give the United States military an enormous advantage. Rare earth metals are key ingredients for making the very hard alloys used in armored vehicles and projectiles that shatter upon impact.

Substitutes can be used for rare earth elements in some defense applications; however, those subsitutes are usually not as effective and that diminishes military superiority. Several uses of rare earth elements are summarized in the table below.

Defense Uses of Rare Earth Elements
Lanthanum night-vision goggles
Neodymium laser range-finders, guidance systems, communications
Europium fluorescents and phosphors in lamps and monitors
Erbium amplifiers in fiber-optic data transmission
Samarium permanent magnets that are stable at high temperatures
Samarium precision-guided weapons
Samarium “white noise” production in stealth technology

Are These Elements Really “Rare”?

Rare earth elements are not as “rare” as their name implies. Thulium and lutetium are the two least abundant rare earth elements – but they each have an average crustal abundance that is nearly 200 times greater than the crustal abundance of gold. However, these metals are very difficult to mine because it is unusual to find them in concentrations high enough for economical extraction.

The most abundant rare earth elements are cerium, yttrium, lanthanum and neodymium. They have average crustal abundances that are similar to commonly used industrial metals such as chromium, nickel, zinc, molybdenum, tin, tungsten and lead. Again, they are rarely found in extract able concentrations.

History of Rare Earth Production and Trade

Pre-1965

Before 1965 there was relatively little demand for rare earth elements. At that time, most of the world’s supply was being produced from placer deposits in India and Brazil. In the 1950s, South Africa became the leading producer from rare earth bearingmonazite deposits. At that time, the Mountain Pass Mine in California was producing minor amounts of rare earth oxides from a Precambrian carbonatite.

Color Television Ignites Demand

The demand for rare earth elements saw its first explosion in the mid-1960s, as the first color television sets were entering the market. Europium was the essential material for producing the color images. The Mountain Pass Mine began producing europium from bastnasite, which contained about 0.1% europium. This effort made the Mountain Pass Mine the largest rare earth producer in the world and placed the United States as the leading producer.

China Enters the Market

China began producing noteable amounts of rare earth oxides in the early 1980s and became the world’s leading producer in the early 1990s. Through the 1990s and early 2000s, China steadily strengthened its hold on the world’s rare earth oxide market. They were selling rare earths at such low prices that the Mountain Pass Mine and many others throughout the world were unable to compete and stopped operation.

Defense and Consumer Electronics Demand

At the same time, world demand was skyrocketing as rare earth metals were designed into a wide variety of defense, aviation, industrial and consumer electronics products. China capitalized on its dominant position and began restricting exports and allowing rare earth oxide prices to rise to historic levels.

China as the Largest Rare Earth Consumer

In addition to being the world’s largest producer of rare earth materials, China is also the dominant consumer. They use rare earths mainly in manufacturing electronics products for domestic and export markets. Japan and the United States are the second and third largest consumers of rare earth materials. It is possible that China’s reluctance to sell rare earths is a defense of their value-added manufacturing sector.

China’s Apex of Production Dominance?

The Chinese dominance may have peaked in 2010 when they controlled about 95% of the world’s rare earth production and prices for many rare earth oxides had risen over 500% in just a few years. That was an awakening for rare earth consumers and miners throughout the world. Mining companies in the United States, Australia, Canada and other countries began to reevaluate old rare earth prospects and explore for new ones.

High prices also caused manufacturers to do three things: 1) seek ways to reduce the amount of rare earth elements needed to produce each of their products; 2) seek alternative materials to use in place of rare earth elements; and, 3) develop alternative products that do not require rare earth elements.

This effort has resulted in a decline in the amounts of rare earth materials used in some types of magnets and a shift from rare earth lighting products to light-emitting diode technology. In the United States, the average consumption of rare earths per unit of manufactured product has decreased but the demand for more products manufactured with rare earth elements has increased. The result has been higher consumption.

China Buying Resources Outside of China

Chinese companies have been purchasing rare earth resources in other countries. In 2009 China Non-Ferrous Metal Mining Company bought a majority stake in Lynas Corporation, an Australian company that has one of the highest outputs of rare earth elements outside of China. They also purchased the Baluba Mine in Zambia.

What is a Glacier?

What is a Glacier?

A glacier is a slowly flowing mass of ice with incredible erosive capabilities. Valley glaciers (alpine glaciers, mountain glaciers) excel at sculpting mountains into jagged ridges, peaks, and deep U-shaped valleys as these highly erosive rivers of ice progress down mountainous slopes. Valley glaciers are currently active in Scandinavia, the Alps, the Himalayas, and in the mountains and volcanoes along the west coasts of North and South America. The amazing, jagged landscape of New Zealand’s Southern Alps is also courtesy of the erosive power of glaciers. The lighting of the signal beacons in the movie The Lord of the Rings – The Return of the King [1] captures this famous landscape.

Continental glaciers (ice sheets, ice caps) are massive sheets of glacial ice that cover landmasses. Continental glaciers are currently eroding deeply into the bedrock of Antarctica and Greenland. The vast ice sheets are incredibly thick and have thus depressed the surface of the land below sea level in many locations. For example, in West Antarctica the maximum ice thickness is 4.36 kilometers (2.71 miles) causing the land surface to become depressed 2.54 kilometers (1.58 miles) below sea level! [2] If all the glacial ice on Antarctica were to melt instantaneously, all that would be visible of Antarctica’s land surface would be large and small landmasses with scattered islands surrounded by the Southern Ocean

Bucher Valley Glacier

Southern Greenland from Space: A small continental glacier covers Greenland. Satellite image by NASA and the United States Geological Survey.

Sampling glacial ice

Sampling Glacial Ice: A scientist collects snow samples from the Taku Glacier of Alaska. Image by the United States Geological Survey.

How Do Glaciers Form?

A considerable amount of snow accumulation is necessary for glacial ice to form. It is imperative that more snow accumulates in the winter than that which melts away during the summer. Snowflakes are hexagonal crystals of frozen water; however, layers of fluffy snowflakes are not glacial ice…not yet at least.

As thick layers of snow accumulate, the deeply buried snowflakes become increasingly more tightly packed together. The dense packing causes the snowflakes to take on rounded shapes as the hexagonal snowflake shape is destroyed. With enough time, the deeply buried, well-rounded grains become very densely packed, expelling most of the air trapped between the grains. The granular snow grains are called firn and take approximately two years to form. [3]

The thick, overlying snowpack exerts tremendous pressure onto the layers of buried firn, and these grains begin to melt a tiny bit. The firn and meltwater slowly recrystallize, forming glacial ice. This transformation process may take several decades to hundreds of years because the rate of glacial ice formation is highly dependent upon the amount of snowfall. (The recrystallization process means that glacial ice is really a type of metamorphic rock.)

zones of a glacier

Tazlina Valley Glacier: Crevasses are visible near the thinning terminus in the zone of wastage. Note that the ice surface is dirty due to the accumulation of sand and gravel particles. Tazlina Valley Glacier in Alaska is retreating. Image by Bruce F. Molnia, USGS. Click the image to enlarge.

zones of a glacier

Zones of a Glacier: A cartoon cross-section through a glacier, showing the zone of accumulation and zone of wastage. Image by the United States Geological Survey.

How Do Glaciers Flow?

A glacier begins to flow when a thick mass of ice begins to deform plastically under its own weight. This process of plastic deformation (internal deformation) occurs because the ice crystals are able to slowly bend and change shape without breaking or cracking. Plastic deformation occurs below a depth of 50 meters (164 feet) from the surface of the glacier. [4]

Thick glacial ice is quite heavy, and the great weight of the glacier may cause the ice along the base of the glacier to melt. Melting occurs because the temperature at which ice melts is reduced due to the pressure exerted by the weight of the overlying glacial ice. Heat from the Earth’s surface may also cause ice to melt along the base of the glacier. The process of basal sliding occurs when a thin layer of meltwater accumulates between the basal ice and the Earth’s surface. The meltwater functions as a lubricant allowing the glacier to slide more readily over bedrock and sediments.

If a great deal of slippery meltwater accumulates under the ice, the glacier may begin to advance very rapidly as a surge. Sometimes known as a galloping glacier, a surging glacier flows at a very rapid rate. For example, in the summer of 2012, Jakobshavn Glacier, located on the east coast of Greenland, was measured to be advancing at a rate of 46 meters per day (151 feet/day). [5] Jakobshavn Glacier is widely believed to be responsible for generating the large iceberg that ultimately sank the Titanic in 1912.

Sampling glacial ice

Before and After Photos: Photos taken at the same location location in Glacier Bay National Park and Preserve in Alaska. The upper photo shows Muir Glacier in the 1880’s and the lower photo shows the same inlet in 2005. Muir Glacier has retreated 50 kilometers (31 miles). Both images by the United States Geological Survey.

What Are the Zones of a Glacier?

The area of glacial ice formation is called the zone of accumulation. In this zone more snow accumulates each winter than that which melts away during the summer. Buried accumulations of snow turn into firn and eventually recrystallize into glacial ice. Glacial ice flows away from the zone of accumulation when the thick ice deforms plastically under its own weight. In a valley glacier the ice flows downslope from the zone of accumulation, while for a continental glacier the ice flows laterally outward and away from the zone of accumulation.

The area of a glacier that experiences a greater amount of melting than glacial ice formation is called the zone of wastage (zone of ablation). In this zone, as the ice melts away, bits of sand and gravel on the surface of the glacier are left behind. It is important to note that glacial ice is always replenishing this zone as glacial ice continues to flow from the zone of accumulation.

The line that separates the zone of accumulation from the zone of wastage is called the snow line (equilibrium line). The snow line may be visible at the end of summer between the clean icy surface of the zone of accumulation and the dirty, sediment-covered surface of the zone of wastage.

The upper 50 meters of the surface of the glacier, where the ice does not undergo plastic deformation, is referred to as the zone of fracture. In this zone the ice is brittle and only deforms by cracking, breaking, and fracturing. Crevasses are fractures or breaks in the ice that may be hundreds of meters long and up to 50 meters deep. [4]

The end or toe of the glacier is called the terminus and is part of the zone of wastage. When the terminus of the glacier flows into a body of water, the ice at the toe calves or breaks off to form floating chunks of ice called icebergs.

John Muir wrote about one of his 1880 adventures in Alaska, when he and the camp dog, Stickeen, went on a lengthy hike up a valley glacier [6]. On the return trip their way was barred by crevasses, and John had to walk a considerable distance until he discovered a precarious, narrow ice bridge spanning a deep crevasse. Understandably, Stickeen was quite reluctant to traverse the dangerous bridge of ice and John spent considerable time and effort coaxing the fearful dog to cross. Stickeen and John eventually returned safely to camp only to be accosted by his fellow campers who were quite upset with him. John had failed to let anyone know where he was going!

Why

Cirques: Two cirques containing small valley glaciers are separated by an arête. Glacier Bay National Park, Alaska. Image by the United States Geologial Survey.

Why Do Glaciers Advance and Retreat?

Glaciers have a snow budget, much like a monetary bank account. The more money deposited into a bank account, the larger the account grows. However, if more money is removed than is deposited into the account, the amount of available money is much reduced. Glacial ice advancement and retreat is quite similar.

When more glacial ice forms in the zone of accumulation than that which melts away in the zone of wastage, the glacier will grow and advance. The terminus of an advancing glacier will progress farther away from the zone of accumulation and thus lengthen the glacier.

A glacier retreats when more ice melts away during the summer than that which forms during the winter. The glacier reduces in size as the ice in the zone of wastage melts. The retreating glacial ice never actually flows backwards; the ice simply melts away faster than is replenished from new glacial ice formation in the zone of accumulation.

If the amount of glacial ice formation in the zone of accumulation equals the amount of melting in the zone of wastage, then the glacier does not advance or retreat. While the ice within the glacier continues to flow away form the source toward the terminus, the toe of the glacier will stand stationary because the glacial ice budget balances between the two zones.

The Sliding Rocks of Racetrack Playa

The Sliding Rocks of Racetrack Playa,

 

The Sliding Rocks Mystery

One of the most interesting mysteries of Death Valley National Park is the sliding rocks at Racetrack Playa (a playa is a dry lake bed). These rocks can be found on the floor of the playa with long trails behind them. Somehow these rocks slide across the playa, cutting a furrow in the sediment as they move.

Some of these rocks weigh several hundred pounds. That makes the question: “How do they move?” a very challenging one.

About Racetrack Playa

Racetrack playa is lake bed that is almost perfectly flat and almost always dry. It is about 4 kilometers long (2.5 miles) – north to south and about 2 kilometers wide (1.25 miles) east to west. The surface is covered with mud cracks and the sediment is made up mainly of silt and clay.

The climate in this area is arid. It rains just a couple of inches per year. However, when it rains, the steep mountains which surround Racetrack Playa produce a large amount of runoff that converts the playa floor into a broad shallow lake that might be just a few inches deep at the low point of the playa. When wet, the surface sediments of the playa are transformed into a very soft and very slippery mud. When the mud dries out, mud cracks that typically cover the floor of the playa are formed.

Are They Moved by People or Animals?

The shape of trails behind the rocks suggest that they move during times when the floor of Racetrack Playa is covered with a very soft mud. A lack of disturbed mud around the rock trails eliminates the possibility of a human or animal pushing or assisting the motion of the rocks.

Are They Moved by Wind?

This was once the favorite explanation. The prevailing winds that blow across Racetrack Playa blow from the southwest to the northeast. Most of the rock trails are parallel to this direction. This is strong evidence that wind might be the force that moves the rocks or is at least involved with the motion of the rocks.

Strong wind gusts or “hurricane force winds” were originally thought to nudge the rocks into motion. This was thought to occur when the playa was very wet, immediately after a rain that converted the surface of the playa into a slippery mud. Once a rock began to move a wind of much lower velocity could keep it in motion as it slid across the soft and very slippery mud. Curves in the rock trails were explained by shifts in wind direction or in how the wind interacted with an irregularly-shaped rock.

The problem with the wind moving the rocks is that many of the rocks weigh several hundred pounds and are embedded a few inches into the mud of the playa. It is unlikely that wind alone could move these large rocks.

Rocks of many shapes leave trails across Racetrack Playa.

Are They Moved by Ice?

Rarely, about once every several years, the occasional shallow lake that covers the surface of Racetrack Playa freezes over, covering the playa with a thin layer of ice, floating on a thin layer of water. Could a wind, blowing across the surface of the ice, move the ice, along with the embedded rocks, across the surface of the playa? The moving rocks would cut furrows into the surface of the playa, which, after the ice melts and the water recedes, would becomes the trails seen by visitors to the playa when the weather improves.

Sometimes multiple neighboring rocks have trails that seem to have simultaneously change directions. These highly congruent trails on multiple rocks strongly support the “wind moving rocks embedded in an ice sheet” theory. One of the first reports that provided strong evidence of the rocks being moved this way is a 2006 video by Brian Dunning.

How the Mystery Was Solved!

Until 2013, all of the best explanations involved wind as the energy source and an ice sheet that captures enough wind energy to drag a six-hundred pound rock across the surface of the playa. The big break in solving the mystery occurred in November 2013 when a lake up to three inches deep covered the playa and then froze. Researchers then observed many ice-embedded rocks moving slowly across the playa on several dates in December 2013 and January 2014. This evidence of the rocks in motion has been shared in a video by the Scripps Institution of Oceanography.

By February 2014 the lake had dried up and new trails left by the recently-moved rocks could be seen in the playa sediment surface. Some of the rocks had been equipped with a small GPS recorder and their records indicate that some rocks had moved over seven hundred feet during at least four episodes of movement.

This work demonstrated the movement of the rocks and attributed it to wind moving the rocks while they were embedded in a large ice sheet floating on a thin layer of water. Finally the mystery was solved!

Photos of the “Sliding Rocks” !

Movement of a large rock across a barren surface is almost impossible to believe. Several good photos of large rocks and their trails by Steve Geer, Stephan Hoerold, David Choo, Skye Bajoul, sartriano, John Alcorn and Mike Nortan are posted on this page for those who are unable to travel to Death Valley National Park.

Lots of sliding rocks and trails on Racetrack Playa

What is Earth Science?

What is Earth Science?

 

Introduction

Earth Science is the study of the Earth and its neighbors in space. It is an exciting science with many interesting and practical applications. Some Earth scientists use their knowledge of the Earth to locate and develop energy and mineral resources. Others study the impact of human activity on Earth’s environment and design methods to protect the planet. Some use their knowledge about Earth processes such as volcanoes, earthquakes and hurricanes to plan communities that will not expose people to these dangerous events.

The Four Earth Sciences

Many different sciences are used to learn about the earth, however, the four basic areas of Earth science study are: geology, meteorology, oceanography and astronomy. A brief explanation of these sciences is provided below.

Geology: Science of the Earth

Geology is the primary Earth science. The word means “study of the Earth”. Geology deals with the composition of Earth materials, Earth structures, and Earth processes. It is also concerned with the organisms of the planet and how the planet has changed over time. Geologists search for fuels and minerals, study natural hazards, and work to protect Earth’s environment.

Meteorology: Science of the Atmosphere

Meteorology is the study of the atmosphere and how processes in the atmosphere determine Earth’s weather and climate. Meteorology is a very practical science because everyone is concerned about the weather. How climate changes over time in response to the actions of people is a topic of urgent worldwide concern. The study of meteorology is of critical concern for protecting Earth’s environment.

Oceanography: Science of the Oceans

Oceanography is the study of Earth’s oceans – their composition, movement, organisms and processes. The oceans cover most of our planet and are important resources for food and other commodities. They are increasingly being used as an energy source. The oceans also have a major influence on the weather and changes in the oceans can drive or moderate climate change. Oceanographers work to develop the ocean as a resource and protect it from human impact. The goal is to utilize the oceans while minimizing the effects of our actions.

Astronomy: Science of the Universe

Astronomy is the study of the universe. Here are some examples of why studying space beyond Earth is important: the moon drives the ocean’s tidal system, asteroid impacts have repeatedly devastated Earth’s inhabitants and energy from the sun drives our weather and climates. A knowledge of astronomy is essential to understanding the Earth. Astronomers can also use a knowledge of Earth materials, processes and history to understand other planets – even those outside of our own solar system.

The Importance of Earth Science

Today we live in a time when the Earth and its inhabitants face many challenges. Our climate is changing and that change is being caused by human activity. Earth scientists recognized this problem and will play a key role in efforts to resolve it. We are also challenged to: develop new sources of energy that will have minimal impact on climate; locate new sources of metals and other mineral resources as known sources are depleted; and, determine how Earth’s increasing population can live and avoid serious threats such as volcanic activity, earthquakes, landslides, floods and more. These are just a few of the problems where solutions depend upon a deep understanding of Earth science.

Earth Science Careers

If you are a pre-college student you can start preparing for a career in Earth science by enrolling in the college preparation program and doing well in all of your courses. Science courses are especially important but math, writing, and other disciplines are also used by Earth scientists during every working day.

GOLD!!!

Gold

A brief history of gold uses, prospecting, mining and production.

Uses of Gold in the Ancient World

Gold was among the first metals to be mined because it commonly occurs in its native form, that is, not combined with other elements, because it is beautiful and imperishable, and because exquisite objects can be made from it. Artisans of ancient civilizations used gold lavishly in decorating tombs and temples, and gold objects made more than 5,000 years ago have been found in Egypt. Particularly noteworthy are the gold items discovered by Howard Carter and Lord Carnarvon in 1922 in the tomb of Tutankhamun. This young pharaoh ruled Egypt in the 14th century B.C. An exhibit of some of these items, called “Treasures of Tutankhamun,” attracted more than 6 million visitors in six cities during a tour of the United States in 1977-79.

The graves of nobles at the ancient Citadel of Mycenae near Nauplion, Greece, discovered by Heinrich Schliemann in 1876, yielded a great variety of gold figurines, masks, cups, diadems, and jewelry, plus hundreds of decorated beads and buttons. These elegant works of art were created by skilled craftsmen more than 3,500 years ago.

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Ancient Gold Sources

The ancient civilizations appear to have obtained their supplies of gold from various deposits in the Middle East. Mines in the region of the Upper Nile near the Red Sea and in the Nubian Desert area supplied much of the gold used by the Egyptian pharaohs. When these mines could no longer meet their demands, deposits elsewhere, possibly in Yemen and southern Africa, were exploited.

Artisans in Mesopotamia and Palestine probably obtained their supplies from Egypt and Arabia. Recent studies of the Mahd adh Dhahab (meaning “Cradle of Gold”) mine in the present Kingdom of Saudi Arabia reveal that gold, silver, andcopper were recovered from this region during the reign of King Solomon (961-922 B.C.).

The gold in the Aztec and Inca treasuries of Mexico and Peru believed to have come from Colombia, although some undoubtedly was obtained from other sources. The Conquistadores plundered the treasuries of these civilizations during their explorations of the New World, and many gold and silver objects were melted and cast into coins and bars, destroying the priceless artifacts of the Indian culture.

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Gold as a Medium of Exchange

Nations of the world today use gold as a medium of exchange in monetary transactions. A large part of the gold stocks of the United States is stored in the vault of the Fort Knox Bullion Depository. The Depository, located about 30 miles southwest of Louisville, Kentucky, is under the supervision of the Director of the Mint.

Gold in the Depository consists of bars about the size of ordinary building bricks (7 x 3 5/8 x 1 3/4 inches) that weigh about 27.5 pounds each (about 400 troy ounces; 1 troy ounce equals about 1.1 avoirdupois ounces.) They are stored without wrappings in the vault compartments.

Aside from monetary uses, gold, like silver, is used in jewelry and allied wares, electrical-electronic applications, dentistry, the aircraft-aerospace industry, the arts, and medical and chemical fields.

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Gold Price Regulation and Variability

The changes in demand for gold and supply from domestic mines in the past two decades reflect price changes. After the United States deregulated gold in 1971, the price increased markedly, briefly reaching more than $800 per troy ounce in 1980. Since 1980, the price has remained in the range of $320 to $460 per troy ounce. The rapidly rising prices of the 1970’s encouraged both experienced explorationists and amateur prospectors to renew their search for gold. As a result of their efforts, many new mines opened in the 1980’s, accounting for much of the expansion of gold output. The sharp declines in consumption in 1974 and 1980 resulted from reduced demands for jewelry (the major use of fabricated gold) and investment products, which in turn reflected rapid price increases in those years.

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Properties of Gold

Gold is called a “noble” metal (an alchemistic term) because it does not oxidize under ordinary conditions. Its chemical symbol Au is derived from the Latin word “aurum.” In pure form gold has a metallic luster and is sun yellow, but mixtures of other metals, such as silver, copper, nickel, platinum, palladium, tellurium, and iron, with gold create various color hues ranging from silver-white to green and orange-red.

Pure gold is relatively soft–it has about the hardness of a penny. It is the most malleable and ductile of metals. The specific gravity or density of pure gold is 19.3 compared to 14.0 for mercury and 11.4 for lead.

Impure gold, as it commonly occurs in deposits, has a density of 16 to 18, whereas the associated waste rock (gangue) has a density of about 2.5. The difference in density enables gold to be concentrated by gravity and permits the separation of gold from clay, silt, sand, and gravel by various agitating and collecting devices such as the gold pan, rocker, and sluicebox.

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Gold Amalgam

Mercury (quicksilver) has a chemical affinity for gold. When mercury is added to gold-bearing material, the two metals form an amalgam. Mercury is later separated from amalgam by retorting. Extraction of gold and other precious metals from their ores by treatment with mercury is called amalgamation. Gold dissolves in aqua regia, a mixture of hydrochloric and nitric acids, and in sodium or potassium cyanide. The latter solvent is the basis for the cyanide process that is used to recover gold from low-grade ore.

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Fineness, Karats and Troy Ounces

The degree of purity of native gold, bullion (bars or ingots of unrefined gold), and refined gold is stated in terms of gold content. “Fineness” defines gold content in parts per thousand. For example, a gold nugget containing 885 parts of pure gold and 115 parts of other metals, such as silver andcopper, would be considered 885-fine. “Karat” indicates the proportion of solid gold in an alloy based on a total of 24 parts. Thus, 14-karat (14K) gold indicates a composition of 14 parts of gold and 10 parts of other metals. Incidentally, 14K gold is commonly used in jewelry manufacture. “Karat” should not be confused with “carat,” a unit of weight used for precious stones.

The basic unit of weight used in dealing with gold is the troy ounce. One troy ounce is equivalent to 20 troy pennyweights. In the jewelry industry, the common unit of measure is the pennyweight (dwt.) which is equivalent to 1.555 grams.

The term “gold-filled” is used to describe articles of jewelry made of base metal which are covered on one or more surfaces with a layer of gold alloy. A quality mark may be used to show the quantity and fineness of the gold alloy. In the United States no article having a gold alloy coating of less than 10-karat fineness may have any quality mark affixed. Lower limits are permitted in some countries.

No article having a gold alloy portion of less than one-twentieth by weight may be marked “gold-filled,” but articles may be marked “rolled gold plate” provided the proportional fraction and fineness designations are also shown. Electroplated jewelry items carrying at least 7 millionths of an inch (0.18 micrometers) of gold on significant surfaces may be labeled “electroplate.” Plated thicknesses less than this may be marked “gold flashed” or “gold washed.”

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Formation of Primary Gold Deposits – Lode Gold

Gold is relatively scarce in the earth, but it occurs in many different kinds of rocks and in many different geological environments. Though scarce, gold is concentrated by geologic processes to form commercial deposits of two principal types: lode (primary) deposits and placer (secondary) deposits.

TYPES OF GOLD:

    • White Gold
        : For gold to take a white color, it must be mixed with a white metal such as nickel, manganese or palladium. Standard White gold is usually 14K of gold (58.5% purity) while the rest is divided as 21% copper, 7.84% zinc, and 12.73% nickel. and White gold can often be rhodium plated to give it a more shiny and white appearance.
    • Rose, Pink, Red Gold
        : Gold can take these colors when mixed with copper. The more copper in the alloy, the darker the tone of red that will surface. A common rose gold alloy composition is 18K (75% gold) mixed with 25% copper while a 50/50 mix of gold (12K) with copper results in what we would call red gold.
  • Green Gold
      : Green gold, otherwise known as

electrum

        , is a natural forming alloy which combines gold and silver. The greenish color varies depending on the exact mixture but back in the 73% gold, 27% silver
    • Blue Gold
        : 46% gold, 54% indium.
    • Purple Gold
        : 80% gold, 20% aluminum.
    • Black Gold

: 75% gold, 25% cobalt.

    Pictures:
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