Facts about Gold

Gold, like no other metal, has a fascinating history and a special place in the world.  For thousands of years it has been used as an ornament of kings, a currency and standard for global currencies, and more recently, in a wide range of electronic devices and medical applications.

Gold's many unique properties have secured it a central role in history and human development. Gold is a remarkable, rare metal, with an unparalleled combination of chemical and physical properties. It is the only yellow metal and bears its name from the Old English word for yellow, 'geolu'. It is also the only metal that forms no oxide film on it's surface in air at normal temperatures, meaning that it will never rust or tarnish.

Gold's chemical symbol, Au, comes from the latin word for gold, aurum. In the Periodic Table of Elements, gold is classified as a transitional metal with the following characteristics:

Symbol: Au Atomic number: 79 Atomic mass: 196.96655 amu Number of protons/electrons: 79 Number of neutrons: 118 Melting point: 1,064.43°C (1,337.58°K, 1,947.97°F) Boiling point: 2,807.0°C (3,80.15°K, 5,084.6°F) Density @ 293°K: 19.32 grams per cubic centimeter Crystal structure: cubic oxidation states: +1, +3

Atomic Structure Shells: 2,8,18,32,18,1

Like other transition metals gold's valence electrons, or the electrons it uses to combine with other elements, are present in more than one shell. Unusually for a metal, gold can also form compounds (aurides) in which its oxidation number is negative (-1). For example, gold can combine with cesium to form cesium auride, CsAu, and rubidium to form rubidium auride, RbAu. These are ionic compounds with non-metallic properties in which the Cs or Rb ions are charged +1 while the Au atoms are charged 1-.

Gold may be alloyed with various other metals to give it special properties. In its pure form, gold has a metallic luster and is sun yellow, but when mixed or alloyed with other metals, such as silver (Ag), copper (Cu), zinc (Zn), nickel (Ni), platinum (Pt), palladium (Pd), tellurium (Te), and iron (Fe), creates various color hues ranging from silver-white to green and orange-red. Usually, red, yellow and green golds are made by adding varying amounts of copper (Cu) and silver (Ag) to produce alloys of 10 to 14 carats. White golds have traditionally been made by alloying nickel (Ni), zinc (Zn) and copper (Cu) with gold, but more recently silver (Ag) and palladium (Pd) have replaced the zinc. These color variation treatments to gold are mostly used in jewelry.

Gold is found in nature in quartz veins and secondary alluvial deposits as a free metal or in a combined state. It is widely distributed although it is rare, being 75th in order of abundance of the elements in the crust of the Earth. It is almost always associated with varying amounts of silver; the naturally occurring gold-silver alloy is called electrum. Gold occurs, in chemical combination with tellurium, in the minerals calaverite and sylvanite along with silver, and in the mineral nagyagite along with lead, antimony, and sulfur. It occurs with mercury as gold amalgam. It is generally present to a small extent in iron pyrites; galena, the lead sulfide ore that usually contains silver, sometimes also contains appreciable amounts of gold. Gold also occurs in seawater to the extent of 5 to 250 parts by weight to 100 million parts of water. Although the quantity of gold present in seawater is more than 9 billion metric tons, the cost of recovering the gold would be far greater than the value of the gold that could thus be recovered.

Properties of Gold

Khrysos (Gold) is a child of Zeus; neither moth nor rust devoureth it; but the mind of man is devoured by this supreme possession. - 5th century Greek fragment.

The crystal structure for metallic gold is face centred cubic. This crystal structure contributes to gold's very high ductility since the lattices are particularly suitable for allowing the movement of dislocations in the lattice.

An unparalleled combination of chemical and physical properties make gold invaluable to a wide range of everyday applications. One of the most important of these properties is gold's virtual indestructibility. Gold is the most non-reactive of all metals. It is called a "noble" metal (an alchemistic term) because it does not oxidize under ordinary conditions, meaning that it will never rust and never tarnish.It will, however, dissolve in aqueous mixtures containing various halogens such as chlorides, bromides, or some iodides. It will also dissolve in some oxidizing mixtures, such as cyanide ion with oxygen, and in aqua regia, a mixture of hydrochloric and nitric acids.

Gold's physical properties of high electrical conductivity and chemical inertness make it an excellent and reliable conductor, particularly in harsh environments, where temperatures can range from -55°C to 200°C. The use of gold in circuitry ensures reliability of equipment operation, particularly in the vital activation of safety airbag mechanisms in motor vehicles or deployment of satellites and spacecraft.No other metal is as ductile or as malleable as gold. A single ounce of the metal can be drawn into a wire five miles long. Gold can be hammered into sheets so thin that light can pass through. High purity gold reflects infrared (heat) energy almost completely, making it ideal for heat and radiation reflection. Gold-coated visors protected astronauts' eyes from searing sunlight on the Apollo 11 moon landing. Gold is also an excellent conductor of thermal energy. It is used in many electronic processes to draw heat away from delicate instruments. For example, the main engine nozzle of the space shuttle uses a 35% gold alloy.

Gold Colors

Gold is bright yellow and has a high luster. Apart from copper it is the only non white colored metal. Gold’s attractive warm colour has led to its widespread use in decoration.

The arrangement of outer electrons around the gold nucleus is the reason for the yellow color; to be precise, the transition of electrons from the d band to unoccupied positions in the conduction band.

Finely divided gold, like other metallic powders, is black; colloidally suspended gold ranges in color from ruby red to purple.Gold can mixed with other metals to give it different colors.

White gold is very popular right now. It can be in 18-karat or 14-karat gold (but not in 22-karat, as it is yellow gold). There are two basic types of white gold alloys: white gold mixed with nickel and white gold mixed with palladium. Nickel can be mixed with gold to create a white or gray color, but some people have an allergy to nickel. Palladium is another metal used to create white gold. Palladium is better but it costs more.

Copper creates pink and rose tones in gold.The more the copper, the deeper will be the effect.

Greenish shades are created by adding silver to gold.

Rose gold and Green gold can be 18-karat or 14-karat but the color is stronger in the 14-karat alloys.

Purple gold. It is referred as amethyst or violet gold. Purple gold is obtained by mixing gold and aluminium in a certain fixed ratio. Gold content is almost 79% and therefore it is qualified to be referred to as 18K gold.

Blue gold is made as an inter-metallic compound between gold and indium . The gold gets a bluish hue color with this process.

Black gold is created using a few techniques. Electro-deposition using black rhodium or ruthenium is the first technique. Controlled oxidation of Carat gold containing cobalt or chromium can also be made to create black gold. Amorphous carbon is also used some times, with the Plasma Assisted Chemical Vapor Deposition process.

Uses of Gold

Gold has been prized by people since the earliest times for making statues and icons and also for jewelry to adorn their bodies. Intricately sculptured art objects and adornment jewelry have been uncovered in the Sumerian royal Tombs in southern Iraq and the tombs of Egyptian kings. Significant buildings and religious temples and statues have been covered with thinly beaten sheets of gold. Due to its rarity, gold has long been considered a symbol of the wealth and power of its possessor.

The following table gives recent demand for gold in tonnes.

Gold jewelry is universally popular, loved for its lustrous yellow color and untarnishing character. In many Asian countries, such as India, Thailand, and China, gold is important to religious ceremonies and social occasions, such as the Chinese New Year and Hindu marriages in India.Importantly, gold is still regarded throughout much of the world as a store of financial value, particularly in many developing countries. However it has many other vital uses in modern life.

Due to its high electrical conductivity, gold is a vital component of many electrical devices, including computers. It is used in the manufacture of approximately 50 million computers each year, as well as millions of televisions, DVDs, VCRs, video cameras and mobile phones. Gold has been used in medicine since 1927, when it was found to be useful in the treatment of rheumatoid arthritis. Even before then it was used in dentistry, in fillings and false teeth. Because it is non-toxic and biologically benign, gold is perfect for many medical applications. Surgeons use gold instruments to clear blocked coronary arteries. In another medical procedure, gold pellets are injected into the body to help obstruct the spread of prostate cancer in men. Gold is also used in lasers, which allow surgeons to seal wounds quickly or treat once-inoperable heart conditions. Thin gold wires are used in many surgical procedures to provide strong and inert support. Gold is also used in the form of gold leaf in the arts of gilding and lettering. Purple of Cassius, a precipitate of finely divided gold and stannic hydroxide formed by the interaction of auric chloride and stannous chloride, is used in coloring ruby glass.

Origins of gold

No one is completely sure where gold comes from. The relative average abundance in our Solar System appears higher than can be made in the early universe, in stars, and even in typical supernova explosions. Some astronomers now suggest that neutron-rich heavy elements such as gold might be most easily made in rare neutron-rich explosions such as the collision of neutron stars. Since neutron star collisions are also suggested as the origin of short duration gamma-ray bursts, if you own some gold it is possible that you have a souvenir from one of the most powerful explosions in the universe.

Gold is widespread in low concentrations in all igneous rocks and has been discovered on every continent on earth Its abundance in the Earth's crust is estimated at about 0.005 parts per million. It is 75th in order of abundance of the elements in the crust of the Earth.It occurs mostly in the native state, remaining chemically uncombined except with tellurium, selenium, and possibly bismuth. The element's only naturally occurring isotope is gold-197. Two types of deposits containing significant amounts of gold are known: hydrothermal veins, where it is associated with quartz and pyrite (fool's gold); and placer deposits, both consolidated and unconsolidated, that are derived from the weathering of gold-bearing rocks.

The origin of enriched veins is not fully known, but it is believed that the gold was carried up from great depths with other minerals, at least in partial solid solution, and later precipitated. The gold in rocks usually occurs as invisible disseminated grains, more rarely as flakes large enough to be seen, and even more rarely as masses or veinlets. Crystals about 2.5 cm (1 inch) or more across have been found in California. Masses, some on the order of 90 kg (200 pounds), have been reported from Australia.

Gold occurs mostly in the native state, remaining chemically uncombined except with tellurium, selenium, and possibly bismuth. Gold is almost always associated with varying amounts of silver; the naturally occurring gold-silver alloy is called electrum. Gold often occurs in association with copper and lead deposits, and, though the quantity present is often extremely small, it is readily recovered as a by-product in the refining of those base metals. Large masses of gold-bearing rock rich enough to be called ores are unusual. Gold also occurs in seawater to the extent of 5 to 250 parts by weight to 100 million parts of water. Although the quantity of gold present in seawater is more than 9 billion metric tons, the cost of recovering the gold would be far greater than the value of the gold that could thus be recovered.

Compounds

The characteristic oxidation states of gold are +1 (aurous compounds) and +3 (auric compounds). Gold is more easily displaced from solution by reduction than any other metal; even platinum will reduce Au3+ ions to metallic gold.

Among the relatively few gold compounds of practical importance are gold chloride, AuCl; gold trichloride, AuCl3; and chlorauric acid, HAuCl4. In the first compound gold is in the +1 oxidation state, and in the latter two, the +3 state. All three compounds are involved in the electrolytic refining of gold. Potassium cyanoaurate is the basis for most gold-plating baths (the solution employed when gold is plated). Several organic compounds of gold have industrial applications. For example, gold mercaptides, which are obtained from sulfurized terpenes, are dissolved in certain organic solutions and used for decorating china and glass articles.

How much gold is there?

The best estimates available suggest that the total volume of gold ever mined up to the end of 2006 was approximately 158,000 tonnes, of which around 65% has been mined since 1950. Adding to this the number of tonnes that have been mined since 2006:

2007 2,478
2008 2,414
2009 2,554

gives a total of 165,446 tonnes or 5,319,212,416 ounces. To visualise this imagine a single solid gold cube with edges of about 19 metres (about three metres short of the length of a tennis court). That's all that has ever been produced. The population of the world is 6,692,030,277 so there are 24.72 grams of gold per person on the planet.

[an error occurred while processing this directive]

It is estimated that the total amount of gold yet to be retrieved from the Earth is about 100,000 tons.

Gold Mining

The search for gold used to mean wading in riverbeds to sift gold from the rushing water. Today, gold is mined from the earth, since most of the surface gold – known as alluvial gold – has been found. Gold mining today is largely a matter of technology. First, geologists use geology maps to look for favorable areas to explore. Ore deposits are not easy to find and many of the ones exposed on the surface have already been found. Geologists use the physical and chemical characteristics of the rocks they are looking for to zero in on prospective areas. Once favorable geology is established, remote sensing, airborne and ground geophysics and geochemistry are used to outline targets for drill testing.

Drilling at these sites brings up rock samples from various locations. These samples are analyzed to determine if any gold exists there, the size of the deposit, and the quality of the gold. Using this information, mining engineers determine if enough gold is under the surface to make the mining worthwhile; the type of mine needed; the physical obstacles to getting to the gold; and what impact a mine would have on the area's wildlife and environment. If the gold is close to the surface, the engineers will design an open-pit mine; if the gold is buried deeply, they will plan an underground mine.

Before the gold can be mined, an infrastructure must be created. Even if the gold is close to the surface, the simplest open-pit mine can take up to a year to build. In fact, the time between discovering gold and actually bringing it out of the earth can be up to five years. Since mines are often in remote locations, an entire infrastructure – roads, administrative offices, equipment storage areas, even towns, schools and medical facilities – must be built. The plans for the mines must be given the green light by a number of authorities at each level of government. Also, the mining company must put aside money for reclaiming the land once the gold is mined. In all, the preparation process can end up costing hundreds of millions of dollars – before a single ounce of gold is mined.

Ore samples are taken and examined for the metallurgical quality of the gold in order to determine the appropriate processing technique required to remove the gold. The mine site infrastructure includes a processing area where the ore is crushed and undergoes various processes depending on the nature of the associated minerals and then the loose rock is sent to the appropriate processing location. The process for low-grade ore is relatively simple: a cyanide solution is applied to the heap, dissolving the gold, which is then collected. High-grade ore, on the other hand, heads to the grinding mill for a more extensive process. There are several different ore types which require different processes for optimal recovery of the gold. For example: 1. Oxide ore goes directly to the leaching circuit, where cyanide dissolves the gold. 2. Refractory ore, which contains carbon, is roasted at 1000 degrees Fahrenheit, burning off the sulphide and carbon, then heads to the leaching circuit. 3. Sulphide refractory ore, which does not contain carbon, is oxidized in an autoclave in order to separate the sulphide safely, and in an environmentally friendly manner, from the ore, which then enters the leaching circuit. In the leaching circuit, the gold is extracted from the solution and deposited onto activated carbon, from which the gold is then chemically stripped. The impure gold is then melted into doré bars, which are about 90 percent pure gold. These bars are usually shipped to a refinery where they undergo further processing.

The refining process strips out the remaining impurities from the gold, which is either recycled scrap being upgraded or gold destined to become bullion bars. In the first step, crude gold is melted and treated with chloride, converting remaining metals to chlorides that will drift off the gold. The resulting 99.5 percent pure gold is cast into electrodes known as anodes, which are put into an electrolytic cell. After a current is passed through the cell, the end product is 99.99 percent pure gold.

After a number of years, the gold reserves in a mine will be exhausted. In the old days, a spent mine would be boarded up and abandoned, but nowadays a reclamation project returns the land, as much as possible, to its previous natural state.

Gold as an Investment

Gold gets dug out of the ground in Africa, or someplace, then we melt it down, dig another hole, bury it again and pay people to stand around guarding it. It has no utility. Anyone watching from Mars would be scratching their head. - Warren Buffett

In the West pension funds and mutual funds keep typically around 4% of their assets in gold partly as a hedge against inflation, partly as an alternative to major currencies such as the dollar and partly as an insurance against a major financial crisis. To invest in gold they buy shares in gold mines or futures contracts. In Asian countries many people prefer to keep their savings in gold rather than government paper. They buy gold in the form of jewelry or gold bars.

How has gold performed during your lifetime?

WORLD OFFICIAL GOLD HOLDINGS (June 2009)

[an error occurred while processing this directive]

Properties of Gold

Gold Colors

Uses of Gold

Origins of Gold

Compounds

How much gold is there?

Gold as an investment

Gold Mining

[an error occurred while processing this directive]