RARE Vintage Estate 18K Gold Star Pendant Charm Not Scrap NICE Antique Sterling
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RARE Vintage Estate 18K Gold Star Pendant Charm Not Scrap NICE Antique Sterling :
$14.11
Hi there, I am selling this Amazing 18 K Gold over sterling Cut out Star pendant charm!
LOOK BELOW FOR LARGER PHOTOS!
This pendant weighs 1.27 carats, which is 0.24 grams and it measures 8 mm by 8 mm by 2 mm it is marked with a \" .925 \" and \"china\" on its side, and
it has been tested and tests positively for 18 carat gold jewelry plating over sterling silver!
It is really gorgeous, and it looks perfect and it is in perfect condition!
I have just started this with a , so that it will hopefully go for the most money possible, I am starting it out with a low starting offer.
If you have any questions, do not hesitate to ask me.
Have fun offerding, thanks so much for visiting my sale and have a great day:>)
General propertiesName, symbol, numbergold, Au, 79Pronunciation/ˈɡoʊld/Element categorytransition metalGroup, period, block11,6, dStandard atomic weight196.966569(4)Electron configuration[Xe] 4f14 5d10 6s1Electrons per shell2, 8, 18, 32, 18, 1 (Image)Physical propertiesPhasesolidDensity (near r.t.)19.30 g·cm−3Liquid density at m.p.17.31 g·cm−3Melting point1337.33K, 1064.18°C, 1947.52°FBoiling point3129K, 2856°C, 5173°FHeat of fusion12.55 kJ·mol−1Heat of vaporization324 kJ·mol−1Molar heat capacity25.418 J·mol−1·K−1Vapor pressureP (Pa)1101001 k10 k100 kat T (K)164618142021228126203078Atomic propertiesOxidation states-1, 1, 2, 3, 4, 5
(amphoteric oxide)Electronegativity2.54 (Pauling scale)Ionization energies1st: 890.1 kJ·mol−12nd: 1980 kJ·mol−1Atomic radius144 pmCovalent radius136±6 pmVan der Waals radius166 pmMiscellaneaCrystal structureLattice face centered cubicMagnetic orderingdiamagneticElectrical resistivity(20°C) 22.14 nΩ·mThermal conductivity318W·m−1·K−1Thermal expansion(25 °C) 14.2 µm·m−1·K−1Speed of sound (thin rod)(r.t.) 2030m·s−1Tensile strength120 MPaYoung\'s modulus79 GPaShear modulus27 GPaBulk modulus180 GPaPoisson ratio0.44Mohs hardness2.5Vickers hardness216 MPaBrinell hardness25 HB MPaCAS registry number7440-57-5Most stable isotopesMain article: Isotopes of goldisoNAhalf-lifeDMDE (MeV)DP195Ausyn186.10 dε0.227195Pt196Ausyn6.183 is stable with 118 neutrons198Ausyn2.69517 dβ−1.372198Hg199Ausyn3.169 dβ−0.453199Hgv · d · e · r
Gold (/ˈɡoʊld/) is a chemical element with the symbol Au (from Latin: aurum \"gold\") and an atomic number of 79. Gold is a dense, soft, shiny metal and the most malleable and ductile metal known.[citation needed] Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, as nuggets or grains in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.
Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves in mercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test.
Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. Gold standards have been the most common basis for monetary policies throughout human history, being widely supplanted by fiat currency only in the late 20th century. Gold has also been frequently linked to a wide variety of symbolisms and ideologies. A total of 165,000 tonnes of gold have been mined in human history, as of 2009.[1] This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8500 m3, or a cube 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.[2]
Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry, electronics, and other fields. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity lead to many uses of gold, including electric wiring, colored glass production and even gold leaf eating.
Characteristics
Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of 1 square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.[3] Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in visors of heat-resistant suits, and in sun-visors for spacesuits.[4]
Gold readily creates alloys with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors (see below).[5] Gold is a good conductor of heat and electricity and reflects infrared radiation strongly. Chemically, it is unaffected by air, moisture and most corrosive reagents, and is therefore well suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert.
Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
High quality pure metallic gold is tasteless and scentless, in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).[6]
In addition, gold is very dense, a cubic meter weighing 19,300 kg. By comparison, the density of lead is 11,340kg/m3, and that of the densest element, osmium, is 22,610kg/m3.
ColorDifferent colors of Ag-Au-Cu alloysWhereas most other pure metals are gray or silvery white, gold is yellow. This color is determined by the density of loosely bound (valence) electrons; those electrons oscillate as a collective \"plasma\" medium described in terms of a quasiparticle called plasmon. The frequency of these oscillations lies in the ultraviolet range for most metals, but it falls into the visible range for gold due to subtle relativistic effects that affect the orbitals around gold atoms.[7][8] Similar effects impart a golden hue to metallic cesium (see relativistic quantum chemistry).
Common colored gold alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the triangular diagram to the left. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese, aluminium, iron, indium and other elements can produce more unusual colors of gold for various applications.[5]
IsotopesMain article: Isotopes of goldGold has only one stable isotope, 197Au, which is also its only naturally occurring isotope. Thirty six radioisotopes have been synthesized ranging in atomic mass from 169 to 205. The most stable of these is 195Au with a half-life of 186.1 days. The least stable is 171Au, which decays by proton emission with a half-life of 30 µs. Most of gold\'s radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, and β+ decay. The exceptions are 195Au, which decays by electron capture, and 196Au, which decays most often by electron capture (93%) with a minor β- decay path (7%).[9] All of gold\'s radioisotopes with atomic masses above 197 decay by β- decay.[10]
At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178Au, 180Au, 181Au, 182Au, and 188Au do not have isomers. Gold\'s most stable isomer is 198m2Au with a half-life of 2.27 days. Gold\'s least stable isomer is 177 m2Au with a half-life of only 7 ns. 184 m1Au has three decay paths: β+ decay, isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.[10]
Use and applicationsMonetary exchangeGold has been widely used throughout the world as a vehicle for monetary exchange, either by issuance and recognition of gold coins or other bare metal quantities, or through gold-convertible paper instruments by establishing gold standards in which the total value of issued money is represented in a store of gold reserves.
However, production has not grown in relation to the world\'s economies. Today, gold mining output is declining.[11] With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world\'s gold reserves and their trading market have become a small fraction of all markets and fixed exchange rates of currencies to gold were no longer sustained. At the beginning of World War I the warring nations moved to a fractional gold standard, inflating their currencies to finance the war effort. After World War II gold was replaced by a system of convertible currency following the Bretton Woods system. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, being replaced by fiat currency in their stead. Switzerland was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the International Monetary Fund in 1999.[12]
Pure gold is too soft for day-to-day monetary use and is typically hardened by alloying with copper, silver or other base metals. The gold content of alloys is measured in carats (k). Pure gold is designated as 24k. English gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold, for hardness (American gold coins for circulation after 1837 contained the slightly lower amount of 0.900 fine gold, or 21.6 kt).
InvestmentMain article: Gold as an investmentMany holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions. However, some economists do not believe gold serves as a hedge against inflation or currency depreciation.[13]
The ISO 4217 currency code of gold is XAU.
Modern bullion coins for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although the American Gold Eagle, the British gold sovereign, and the South African Krugerrand continue to be minted in 22k metal in historical tradition. The special issue Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% or 0.99999, while the popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. Several other 99.99% pure gold coins are available. In 2006, the United States Mint began production of the American Buffalo gold bullion coin with a purity of 99.99%. The Australian Gold Kangaroos were first coined in 1986 as the Australian Gold Nugget but changed the reverse design in 1989. Other popular modern coins include the Austrian Vienna Philharmonic bullion coin and the Chinese Gold Panda.
JewelryMain article: JewelleryMoche gold necklace depicting feline heads. Larco Museum Collection. Lima-PeruBecause of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color. Eighteen-carat gold containing 25% copper is found in antique and Russian jewelry and has a distinct, though not dominant, copper cast, creating rose gold. Fourteen-carat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges. Blue gold can be made by alloying with iron and purple gold can be made by alloying with aluminium, although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium or nickel. White 18-carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silvery in appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe. Alternative white gold alloys are available based on palladium, silver and other white metals,[14] but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.
MedicineIn medieval times, gold was often seen as beneficial for the health, in the belief that something that rare and beautiful could not be anything but healthy. Even some modern esotericists and forms of alternative medicine assign metallic gold a healing power.[15] Some gold salts do have anti-inflammatory properties and are used as pharmaceuticals in the treatment of arthritis and other similar conditions.[16] However, only salts and radioisotopes of gold are of pharmacological value, as elemental (metallic) gold is inert to all chemicals it encounters inside the body. In modern times, injectable gold has been proven to help to reduce the pain and swelling of rheumatoid arthritis and tuberculosis.[16][17]
Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys\' slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.
Colloidal gold preparations (suspensions of gold nanoparticles) in water are intensely red-colored, and can be made with tightly controlled particle sizes up to a few tens of nanometers across by reduction of gold chloride with citrate or ascorbate ions. Colloidal gold is used in research applications in medicine, biology and materials science. The technique of immunogold labeling exploits the ability of the gold particles to adsorb protein molecules onto their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the surfaces of cells.[18] In ultrathin sections of tissues viewed by electron microscopy, the immunogold labels appear as extremely dense round spots at the position of the antigen.[19] Colloidal gold is also the form of gold used as gold paint on ceramics prior to firing.
Gold, or alloys of gold and palladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a scanning electron microscope. The coating, which is usually applied by sputtering with an argon plasma, has a triple role in this application. Gold\'s very high electrical conductivity drains electrical charge to earth, and its very high density provides stopping power for electrons in the electron beam, helping to limit the depth to which the electron beam penetrates the specimen. This improves definition of the position and topography of the specimen surface and increases the spatial resolution of the image. Gold also produces a high output of secondary electrons when irradiated by an electron beam, and these low-energy electrons are the most commonly used signal source used in the scanning electron microscope.[20]
The isotope gold-198, (half-life 2.7 days) is used in some cancer treatments and for treating other diseases.[21]
Food and drink- Gold can be used in food and has the E number 175.[22]
- Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.[23] Gold flake was used by the nobility in Medieval Europe as a decoration in food and drinks, in the form of leaf, flakes or dust, either to demonstrate the host\'s wealth or in the belief that something that valuable and rare must be beneficial for one\'s health.
- Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser (English: Goldwater) is a traditional German herbal liqueur[24] produced in what is today Gdańsk, Poland, and Schwabach, Germany, and contains flakes of gold leaf. There are also some expensive (~$1000) cocktails which contain flakes of gold leaf.[25] However, since metallic gold is inert to all body chemistry, it adds no taste nor has it any other nutritional effect and leaves the body unaltered.[26]
- Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing. If the work is to be of hallmarking quality, gold solder must match the carat weight of the work, and alloy formulas are manufactured in most industry-standard carat weights to color match yellow and white gold. Gold solder is usually made in at least three melting-point ranges referred to as Easy, Medium and Hard. By using the hard, high-melting point solder first, followed by solders with progressively lower melting points, goldsmiths can assemble complex items with several separate soldered joints.
- Gold can be made into thread and used in embroidery.
- Gold produces a deep, intense red color when used as a coloring agent in cranberry glass.
- In photography, gold toners are used to shift the color of silver bromide black-and-white prints towards brown or blue tones, or to increase their stability. Used on sepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.[27]
- As gold is a good reflector of electromagnetic radiation such as infrared and visible light as well as radio waves, it is used for the protective coatings on many artificial satellites, in infrared protective in thermal protection suits and astronauts\' helmets and in electronic warfare planes like the EA-6B Prowler.
- Gold is used as the reflective layer on some high-end CDs.
- Automobiles may use gold for heat dissipation. McLaren uses gold foil in the engine compartment of its F1 model.[28]
- Gold can be manufactured so thin that it appears transparent. It is used in some aircraft cockpit windows for de-icing or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to deter ice from forming.[29]
The concentration of free electrons in gold metal is 5.90×1022 cm−3. Gold is highly conductive to electricity, and has been used for electrical wiring in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the Manhattan Project\'s atomic experiments, but large high current silver wires were used in the calutron isotope separator magnets in the project.
Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other Environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin layer coating electrical connectors of all kinds, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables. The benefit of using gold over other connector metals such as tin in these applications is highly debated. Gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy. However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.[30]
Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.[31] Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect semiconductor devices to their packages through a process known as wire bonding.
Commercial chemistryGold is attacked by and dissolves in alkaline solutions of potassium or sodium cyanide, to form the salt gold cyanide—a technique that has been used in extracting metallic gold from ores in the cyanide process. Gold cyanide is the electrolyte used in commercial electroplating of gold onto base metals and electroforming.
Gold chloride (chloroauric acid) solutions are used to make colloidal gold by reduction with citrate or ascorbate ions. Gold chloride and gold oxide are used to make highly valued cranberry or red-colored glass, which, like colloidal gold suspensions, contains evenly sized spherical gold nanoparticles.[32]
HistoryThe Turin Papyrus MapFunerary mask of TutankhamunJason returns with the golden fleece on an Apulian red-figure calyx krater, ca. 340–330 BC.Gold has been known and used by artisans since the Chalcolithic. Gold artifacts in the Balkans appear from the 4th millennium BC, such as that found in the Varna Necropolis. Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.
Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was \"more plentiful than dirt\" in Egypt.[33] Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. The earliest known map is known as the Turin Papyrus Map and shows the plan of a gold mine in Nubia together with indications of the local geology. The primitive working methods are described by both Strabo and Diodorus Siculus, and included fire-setting. Large mines were also present across the Red Sea in what is now Saudi Arabia.
The legend of the golden fleece may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. Gold is mentioned frequently in the Old Testament, starting with Genesis 2:11 (at Havilah) and is included with the gifts of the magi in the first chapters of Matthew New Testament. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets \"made of pure gold, clear as crystal\". The south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world\'s earliest coinage in Lydia around 610 BC.[34] From the 6th or 5th century BC, the Chu (state) circulated the Ying Yuan, one kind of square gold coin.
In Roman metallurgy, new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 106 AD onwards. One of their largest mines was at Las Medulas in León (Spain), where seven long aqueducts enabled them to sluice most of a large alluvial deposit. The mines at Roşia Montană in Transylvania were also very large, and until very recently, still mined by opencast methods. They also exploited smaller deposits in Britain, such as placer and hard-rock deposits at Dolaucothi. The various methods they used are well described by Pliny the Elder in his encyclopedia Naturalis Historia written towards the end of the first century AD.
The Mali Empire in Africa was famed throughout the old world for its large amounts of gold. Mansa Musa, ruler of the empire (1312–1337) became famous throughout the old world for his great hajj to Mecca in 1324. When he passed through Cairo in July 1324, he was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels. He gave away so much gold that it depressed the price in Egypt for over a decade.[35] A contemporary Arab historian remarked:
Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...]—Chihab Al-Umari[36]The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, Ecuador and Colombia. The Aztecs regarded gold as literally the product of the gods, calling it \"god excrement\" (teocuitlatl in Nahuatl).[37] However, for the indigenous peoples of North America, gold was considered useless, and they saw much greater value in other minerals, which were directly related to their utility, such as obsidian, flint, and slate.[38]
Although the price of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Gold as a sign of wealth and prestige was ridiculed by Thomas More in his treatise Utopia. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly dressed of their party.
There is an age-old tradition of biting gold to test its authenticity. Although this is certainly not a professional way of examining gold, the bite test should score the gold because gold is a soft metal, as indicated by its score on the Mohs\' scale of mineral hardness. The purer the gold the easier it should be to mark it. Painted lead can cheat this test because lead is softer than gold (and may invite a small risk of lead poisoning if sufficient lead is absorbed by the biting).
Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.[39] It has been estimated that all gold ever refined would form a single cube 20m (66ft) on a side (equivalent to 8,000 m3).[39]
One main goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called t Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today\'s chemistry. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol and the ancient Chinese character for the Sun. For modern creation of artificial gold by neutron capture, see gold synthesis.
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine near Georgeville, North Carolina in 1803.[40] The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.[41] Further gold rushes occurred in California, Colorado, the Black Hills, Otago in New Zealand, Australia, Witwatersrand in South Africa, and the Klondike in Canada.
Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.
OccurrenceThis 156-ounce (4.85 kg) nugget was found by an individual prospector in the Southern California Desert using a metal detector.Gold\'s atomic number of 79 makes it one of the higher atomic number elements which occur naturally. Like all elements with atomic numbers larger than iron, gold is thought to have been formed from a supernova nucleosynthesis process. Their explosions scattered metal-containing dusts (including heavy elements like gold) into the region of space in which they later condensed into our solar system and the Earth.[42]
On Earth, whenever elemental gold occurs, it appears most often as a metal solid solution of gold with silver, i.e. a gold silver alloy. Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver. Electrum\'s color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity.
Relative sizes of an 860 kg block of gold ore, and the 30 g of gold that can be extracted from it. Toi gold mine, Japan.Gold left behind after a pyrite cube was oxidized to hematite. Note cubic shape of cavity.Gold is found in ores made up of rock with very small or microscopic particles of gold. This gold ore is often found together with quartz or sulfide minerals such as Fool\'s Gold, which is a pyrite.[43] These are called lode deposits. Native gold is also found in the form of free flakes, grains or larger nuggets that have been eroded from rocks and end up in alluvial deposits (called placer deposits). Such free gold is always richer at the surface of gold-bearing veins owing to the oxidation of accompanying minerals followed by weathering, and washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets.
Gold sometimes occurs combined with tellurium as the minerals calaverite, krennerite, nagyagite, petzite and sylvanite, and as the rare bismuthide maldonite (Au2Bi) and antimonide aurostibite (AuSb2). Gold also occurs in rare alloys with copper, lead, and mercury: the minerals auricupride (Cu3Au), novodneprite (AuPb3) and weishanite ((Au, Ag)3Hg2).
Recent research suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.[44]
The world\'s oceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 fmol/L or 10–30 parts per quadrillion (about 10–30 g/km3). In general, Au concentrations for Atlantic and Pacific samples are the same (~50 fmol/L) but less certain. Mediterranean deep waters contain higher concentrations of Au (100–150 fmol/L) attributed to wind-blown dust and/or rivers. At 10 parts per quadrillion the Earth\'s oceans would hold 15,000 tons of gold.[45] These figures are three orders of magnitude less than reported in the literature prior to 1988, indicating contamination problems with the earlier data.
A number of people have claimed to be able to economically recover gold from sea water, but so far they have all been either mistaken or crooks. A so-called reverend, Prescott Jernegan ran a gold-from-seawater swindle in the United States in the 1890s. A British fraudster ran the same scam in England in the early 1900s.[46] Fritz Haber (the German inventor of the Haber process) did research on the extraction of gold from sea water in an effort to help pay Germany\'s reparations following World War I.[47] Based on the published values of 2 to 64 ppb of gold in seawater a commercially successful extraction seemed possible. After analysis of 4,000 water samples yielding an average of 0.004 ppb it became clear that the extraction would not be possible and he stopped the project.[48] No commercially viable mechanism for performing gold extraction from sea water has yet been identified. Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future.
Gallery of specimens of crystalline native goldNative gold nuggets
\"Rope gold\" from Lena River, Sakha Republic, Russia. Size: 2.5×1.2×0.7 cm.
Crystalline gold from Mina Zapata, Santa Elena de Uairen, Venezuela. Size: 3.7×1.1×0.4 cm.
Gold leaf from Harvard Mine, Jamestown, California, USA. Size 9.3×3.2× >0.1 cm.
Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5mg/kg (0.5 parts per million, ppm) can be economical. Typical ore grades in open-pit mines are 1–5mg/kg (1–5 ppm); ore grades in underground or hard rock mines are usually at least 3mg/kg (3 ppm). Because ore grades of 30mg/kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
Since the 1880s, South Africa has been the source for a large proportion of the world\'s gold supply, with about 50% of all gold ever produced having come from South Africa. Production in 1970 accounted for 79% of the world supply, producing about 1,480 tonnes. 2008 production was 2,260 tonnes. In 2007 China (with 276 tonnes) overtook South Africa as the world\'s largest gold producer, the first time since 1905 that South Africa has not been the largest.[49]
The city of Johannesburg located in South Africa was founded as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest gold deposits the world has ever seen. Gold fields located within the basin in the Free State and Gauteng provinces are extensive in strike and dip requiring some of the world\'s deepest mines, with the Savuka and TauTona mines being currently the world\'s deepest gold mine at 3,777 m. The Second Boer War of 1899–1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
Other major producers are the United States, Australia, Russia and Peru. Mines in South Dakota and Nevada supply two-thirds of gold used in the United States. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.[50]
After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations.[51][52] Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution of gold in aqua regia.[53]
At the end of 2009, it was estimated that all the gold ever mined totaled 165,000 tonnes[1] This can be represented by a cube with an edge length of about 20.28 meters. At $1,600 per ounce, 165,000 tons of gold would have a value of $8.8 trillion.
The average gold mining and extraction costs were about US$317/oz in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.[54]
Most of the gold used in manufactured goods, jewelry, and works of art is eventually recovered and recycled. Some gold used in spacecraft and electronic equipment cannot be profitably recovered, but it is generally used in these applications in the form of extremely thin layers or extremely fine wires so that the total quantity used (and lost) is small compared to the total amount of gold produced and stockpiled. Thus there is little true consumption of new gold in the economic sense; the stock of gold remains essentially constant (at least in the modern world) while ownership shifts from one party to another.[55] One estimate is that 85% of all the gold ever mined is still available in the world\'s easily recoverable stocks, with 15% having been lost, or used in non-recyclable industrial uses.[56]
ConsumptionThe consumption of gold produced in the world is about 50% in jewelry, 40% in investments, and 10% in industry.
India is the world\'s largest single consumer of gold, as Indians buy about 25% of the world\'s gold,[57] purchasing approximately 800 tonnes of gold every year, mostly for jewelry. India is also the largest importer of gold; in 2008, India imported around 400 tonnes of gold.[58]
Although gold is a noble metal, it forms many and diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and tertiary phosphines. Au(I) compounds are typically linear. A good example is Au(CN)2−, which is the soluble form of gold encountered in mining. Curiously, aurous complexes of water are rare. The binary gold halides, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.[60]
Au(III) (auric) is a common oxidation state, and is illustrated by gold(III) chloride, Au2Cl6. The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar, with chemical bonds that have both covalent and ionic character.
Aqua regia, a 1:3 mixture of nitric acid and hydrochloric acid, dissolves gold. Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of the reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl4− ions, or chloroauric acid, thereby enabling further oxidation.
Some free halogens react with gold.[61] Gold also reacts in alkaline solutions of potassium cyanide. With mercury, it forms an amalgam.
Less common oxidation statesLess common oxidation states of gold include −1, +2, and +5.
The −1 oxidation state occurs in compounds containing the Au− anion, called aurides. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif.[62] Other aurides include those of Rb+, K+, and tetramethylammonium (CH3)4N+.[63]
Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2. The evaporation of a solution of Au(OH)3 in concentrated H2SO4 produces red crystals of gold(II) sulfate, AuSO4. Originally thought to be a mixed-valence compound, it has been shown to contain Au4+
2 cations.[64][65] A noteworthy, legitimate gold(II) complex is the tetraxenonogold(II) cation, which contains xenon as a ligand, found in [AuXe4](Sb2F11)2.[66]
Gold pentafluoride and its derivative anion, AuF−
6, is the sole example of gold(V), the highest verified oxidation state.[67]
Some gold compounds exhibit aurophilic bonding, which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter that van der Waals bonding. The interaction is estimated to be comparable in strength to that of a hydrogen bond.
Mixed valence compoundsWell-defined cluster compounds are numerous.[63] In such cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au(P(C6H5)3)}62+. Gold chalcogenides, such as gold sulfide, feature equal amounts of Au(I) and Au(III).
Sterling silverFrom Wikipedia, the free encyclopediaJump to: navigation, search This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. (June 2009) Tiffany & Co. pitcher. c. 1871. Pitcher has paneled sides, and repousse design with shells, scrolls and flowers. Top edge is repousse arrowhead leaf design.
Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925.
Fine silver is 99.9% pure and is generally too soft for producing functional objects; therefore, the silver is usually alloyed with copper to give it strength while preserving the ductility and beauty of the precious metal. Other metals can replace the copper, usually with the intent to improve various properties of the basic sterling alloy such as reducing casting porosity, eliminating firescale, and increasing resistance to tarnish. These replacement metals include germanium, zinc and platinum, as well as a variety of other additives, including silicon and boron. A number of alloys, such as Argentium sterling silver, have appeared in recent years, formulated to lessen firescale or to inhibit tarnish, and this has sparked heavy competition among the various manufacturers, who are rushing to make claims of having the best formulation. However, no one alloy has emerged to replace copper as the industry standard, and alloy development is a very active area.
Contents- 1 Etymology
- 2 History
- 3 Hallmarks
- 4 Uses
- 5 Tarnish and corrosion
- 6 References
- 7 External links
One of the earliest attestations of the term is in Old French form esterlin, in a charter of the abbey of Les Préaux, dating to either 1085 or 1104. The English chronicler Orderic Vitalis (1075 – c. 1142) uses the Latin forms libræ sterilensium and libræ sterilensis monetæ. The word in origin refers to the newly introduced Norman silver penny.
According to the Oxford English Dictionary, the most plausible etymology is derivation from a late Old English steorling (with (or like) a \"little star\"), as some early Norman pennies were imprinted with a small star. There are a number of obsolete hypotheses. One suggests a connection with starling, because four birds (in fact martlets) were depicted on a penny of Edward I, and another a supposed connection with Easterling, a term for natives of the Baltic or the Hanse towns of Eastern Germany. This etymology is itself medieval, suggested by Walter de Pinchebek (ca. 1300) with the explanation that the coin was originally made by moneyers from that region.[1]
On the other hand, Philip Grierson, in his essay on Sterling, points out that the stars appeared on Norman pennies only for a single 3-year issue from 1077-80 (the Normans changed coin designs every 3 years), and that the star-theory thus fails on linguistic grounds: extensive research has been done on how coins acquire names, including nicknames. Grierson\'s proposed alternative involves an analogy with the Byzantine solidus, originally known the solidus aureaus meaning \"solid gold\" or \"reliable gold\". Even though English silver pennies had become famous for their consistent weight and purity in the days of Offa, King of Mercia, by the time of the Conquest English coinage had seriously degenerated. One of the first acts of the Normans was to restore the coinage to what it had been in the days of Offa and to maintain it consistently. Grierson thus proposes that \"sterling\" derives from \"ster\"[2] meaning \"strong\" or \"stout\".[3]
History Pair of sterling silver forksThe sterling alloy originated in continental Europe[citation needed] and was being used for commerce as early as the 12th century in the area that is now northern Germany.
In England the composition of sterling silver was subject to official assay at some date before 1158, during the reign of Henry II, but its purity was probably regulated from centuries earlier, in Saxon times. A piece of sterling silver dating from Henry II\'s reign was used as a standard in the Trial of the Pyx until it was deposited at the Royal Mint in 1843. It bears the royal stamp ENRI. REX(\"King Henry\") but this was added later, in the reign of Henry III. The first legal definition of sterling silver appeared in 1275, when a statute of Edward I specified that 12ounces of silver for coinage should contain 11ounces 2¼pennyweights of silver and 17¾pennyweights of alloy.[4]
From about 1840 to somewhere around 1940 in the United States and Europe, sterling silver cutlery [US flatware] became de rigueur when setting a proper table. In fact, there was a marked increase in the number of silver companies that emerged during that period.
The height of the silver craze was during the 50-year period from 1870 to 1920. Flatware lines during this period sometimes included up to 100 different types of pieces. In conjunction with this, the dinner went from three courses to sometimes ten or more. There was a soup course, a salad course, a fruit course, a cheese course, an antipasto course, a fish course, the main course and a pastry or dessert course.
Individual eating implements often included forks (dinner fork, place fork, salad fork, pastry fork, shrimp or cocktail fork), spoons (teaspoon, coffee spoon, demitasse spoon, bouillon spoon, gumbo soup spoon, iced tea spoon) and knives (dinner knife, place knife, butter spreader, fruit knife, cheese knife). This was especially true during the Victorian period, when etiquette dictated nothing should be touched with one\'s fingers.
Serving pieces were often elaborately decorated and pierced and embellished with ivory, and could include any or all of the following: carving knife and fork, salad knife and fork, cold meat fork, punch ladle, soup ladle, gravy ladle, casserole serving spoon, berry spoon, lasagna server, macaroni server, asparagus server, cucumber server, tomato server, olive spoon, cheese scoop, fish knife and fork, pastry server, petit four server, cake knife, bon bon spoon, tiny salt spoon, sugar sifter or caster and crumb remover with brush.
Cutlery sets were often accompanied by tea sets, hot water pots, chocolate pots, trays and salvers, goblets, demitasse cups and saucers, liqueur cups, bouillon cups, egg cups, sterling plates, napkin rings, water and wine pitchers and coasters, candelabra and even elaborate centerpieces.
In fact, the craze with sterling even extended to business (sterling paper clips, mechanical pencils, letter openers, calling card boxes, cigarette cases), to the boudoir (sterling dresser trays, mirrors, hair and suit brushes, pill bottles, manicure sets, shoehorns, perfume bottles, powder bottles, hair clips) and even to children (cups, cutlery, rattles, christening sets).
A number of factors converged to make sterling fall out of favor around the time of World War II. The cost of labor rose (sterling pieces were all still mostly hand made, with only the basics being done by machine). Only the wealthy could afford the large number of servants required for fancy dining with ten courses. And changes in aesthetics resulted in people desiring simpler dinnerware that was easier to clean.
HallmarksOver the years, some countries developed systems of hallmarking silver. The purpose of hallmark application is many fold:
- To indicate the purity of the silver alloy used in the manufacture or hand-crafting of the piece.
- To identify the silversmith or company that made the piece.
- To note the date and/or location of the manufacture or tradesman.
In addition to the uses of sterling silver mentioned above, there are some little known uses of sterling:
- Evidence of silver and/or silver-alloy surgical and medical instruments has been found in civilizations as early as Ur, Hellenistic-era Egypt and Rome, and their use continued until largely replaced in Western countries in the mid to late 20th century by cheaper, disposable plastic items. Its natural malleability is an obvious physical advantage, but it also exhibits medically-specific utility, including the fact that it is naturally aseptic, and, in respect of modern medical practices, it is resistant to antiseptics, heat sterilisation and body fluids.
- Due to sterling silver having a special sound character, some brasswind instrument manufacturers use 92.5% sterling silver as the material for making their instruments, including the flute and saxophone. For example, some leading saxophone manufacturers such as Selmer and Yanagisawa have crafted some of their saxophones from sterling silver, which they believe will make the instruments more resonant and colorful in timbre.
Chemically, silver is not very reactive—it does not react with oxygen or water at ordinary temperatures, so does not easily form a silver oxide. However, it is attacked by common components of atmospheric pollution: silver sulfide slowly appears as a black tarnish during exposure to airborne compounds of sulfur (byproducts of the burning of fossil fuels and some industrial processes), and low level ozone reacts to form silver oxide.[5] As the purity of the silver decreases, the problem of corrosion or tarnishing increases because other metals in the alloy, usually copper, may react with oxygen in the air.
The black silver sulfide (Ag2S) is among the most insoluble salts in aqueous solution, a property that is exploited for separating silver ions from other positive ions.
Sodium chloride (NaCl) or common table salt is known to corrode silver-copper alloy, typically seen in silver salt shakers where corrosion appears around the holes in the top.
Several products have been developed for the purpose of polishing silver that serve to remove sulfur from the metal without damaging or warping it. Because harsh polishing and buffing can permanently damage and devalue a piece of antique silver, valuable items are typically hand-polished to preserve the unique patinas of older pieces. Techniques such as wheel polishing, which are typically performed by professional jewelers or silver repair companies, are reserved for extreme tarnish or buckle
Tools
- Draw metal alloys
- Britannia silver
- Colored gold
- Crown gold
- Electrum
- Platinum sapphire
Organic
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