The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins and jewelry. Coin silver, used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals copper, by mass. Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000 and karats used only for gold. Karats measure the parts per 24, so that 18 karat = 18⁄24 = 75% and 24 karat gold is considered 100% gold. Millesimal fineness is a system of denoting the purity of platinum and silver alloys by parts per thousand of pure metal by mass in the alloy.
For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps rather than "14K", "18K", etc., used in the United Kingdom and United States. It is an extension of the older karat system of denoting the purity of gold by fractions of 24, such as "18 karat" for an alloy with 75% pure gold by mass; the millesimal fineness is rounded to a three figure number where used as a hallmark, the fineness may vary from the traditional versions of purity. Here are the most common millesimal finenesses used for precious metals and the most common terms associated with them. 999.5: what most dealers would buy as if 100% pure. Refined by the Perth Mint in 1957. 999.99—five nines fine: the purest type of gold produced. 999.9—four nines fine: e.g. ordinary Canadian Gold Maple Leaf and American Buffalo coins 999—24 karat occasionally known as three nines fine: e.g. Chinese Gold Panda coins 995: the minimum allowed in Good Delivery gold bars 990—two nines fine 986—Ducat fineness: used by Venetian and Holy Roman Empire mints.
This was achieved by the Royal Silver Company of Bolivia. 999.9—four nines fine: ultra-fine silver used by the Royal Canadian Mint for their Silver Maple Leaf and other silver coins 999—fine silver or three nines fine: used in Good Delivery bullion bars and most current silver bullion coins 980: common standard used in Mexico ca. 1930–45 958: Britannia silver 950: French 1st Standard 935: Swiss standard for watchcases after 1887, to meet the British Merchandise Marks Act and to be of equal grade to 925 Sterling. Sometimes claimed to have arisen as a Swiss misunderstanding of the standard required for British Sterling. Marked with three Swiss bears. 925: Sterling silver equivalent to "plata de primera ley" in Spain 917: a standard used for the minting of Indian silver, during the British raj 900: one nine fine, coin-silver, or 90% silver: e.g. Flowing Hair and 1837–1964 U. S. silver coins 892.4: US coinage 1485⁄1664 fine "standard silver" as defined by the Coinage Act of 1792: e.g. Draped Bust and Capped Bust U.
S. silver coins 875: Swiss standard used for export watchcases. 835: a standard predominantly used in Germany after 1884, for the minting of coins in countries of the Latin Monetary Union 833: a common standard for continental silver among the Dutch and Germans 830: a common standard used in older Scandinavian silver 800: the minimum standard for silver in Germany after 1884. The karat system is a standard adopted by US federal law. K is the karat rating of the material, Mg is the mass of pure gold in the alloy, Mm is the total mass of the material.24-karat gold is pure, 18-karat gold is 18 parts gold, 6 parts another metal, 12-karat gold is 12 parts gold, so forth. In England, the karat was divisible into four grains, the grain was divisible into four quarts. For example, a gold alloy of 127⁄128 fineness could have been described as being 23-karat, 3-grain, 1-quart gold; the karat fractional system is being complemented or superseded by the millesimal system, descr
A coin is a small, round piece of metal or plastic used as a medium of exchange or legal tender. They are standardized in weight, produced in large quantities at a mint in order to facilitate trade, they are most issued by a government. Coins are metal or alloy, or sometimes made of synthetic materials, they are disc shaped. Coins made of valuable metal are stored in large quantities as bullion coins. Other coins are used as money in everyday transactions; the highest value coin in circulation is worth less than the lowest-value note. In the last hundred years, the face value of circulation coins has been lower than the value of the metal they contain, for example due to inflation. If the difference becomes significant, the issuing authority may decide to withdraw these coins from circulation issuing new equivalents with a different composition, or the public may decide to melt the coins down or hoard them. Exceptions to the rule of face value being higher than content value occur for some bullion coins made of copper, silver, or gold, intended for collectors or investors in precious metals.
Examples of modern gold collector/investor coins include the British sovereign minted by the United Kingdom, the American Gold Eagle minted by the United States, the Canadian Gold Maple Leaf minted by Canada, the Krugerrand, minted by South Africa. While the Eagle, Maple Leaf, Sovereign coins have nominal face values, the Krugerrand does not. A great quantity of coinage metals and other materials have been used to produce coins for circulation and metal investment: bullion coins serve as more convenient stores of assured metal quantity and purity than other bullion. Metal ingots, silver bullion or unmarked bars were in use for exchange among many of the civilizations that mastered metallurgy; the weight and purity of bullion would be the key determinant of value. In the Achaemenid Empire in the early 6th century BC, coinage was yet unknown, barter and to some extent silver bullion was used instead for trade; the practice of using silver bars for currency seems to have been current in Central Asia from the 6th century BC.
Coins were an evolution of "currency" systems of the Late Bronze Age, where standard-sized ingots, tokens such as knife money, were used to store and transfer value. In the late Chinese Bronze Age, standardized cast tokens were made, such as those discovered in a tomb near Anyang; these were replicas in bronze of earlier Chinese currency, cowrie shells, so they were named Bronze Shell. The earliest coins are associated with Iron Age Anatolia of the late 7th century BC, with the kingdom of Lydia. Early electrum coins were not standardized in weight, in their earliest stage may have been ritual objects, such as badges or medals, issued by priests; the unpredictability of the composition of occurring electrum implied that it had a variable value, which hampered its development. Most of the early Lydian coins include no writing, only an image of a symbolic animal. Therefore, the dating of these coins relies on archaeological evidence, with the most cited evidence coming from excavations at the Temple of Artemis at Ephesus called the Ephesian Artemision, site of the earliest known deposit of electrum coins.
Because the oldest lion head "coins" were discovered in that temple, they do not appear to have been used in commerce, these objects may not have been coins but badges or medals issued by the priests of that temple. Anatolian Artemis was the Πὀτνια Θηρῶν, it took some time before ancient coins were used for trade. The smallest-denomination electrum coins worth about a day's subsistence, would have been too valuable for buying a loaf of bread; the first coins to be used for retailing on a large-scale basis were small silver fractions, Ancient Greek coinage minted by the Ionian Greeks in the late sixth century BC. Many early Lydian and Greek coins were minted under the authority of private individuals and are thus more akin to tokens or badges than to modern coins, though due to their numbers it is evident that some were official state issues; the earliest inscribed coins are those of Phanes, dated to 625–600 BC from Ephesus in Ionia, with the legend ΦΑΝΕΟΣ ΕΜΙ ΣΗΜΑ, or just bearing the name ΦΑΝΕΟΣ.
The first electrum coins issued by a monarch are those minted by king Alyattes of Lydia, for which reason this king is sometimes mentioned as the originator of coinage. The successor of Alyattes, king Croesus, became associated with great wealth in Greek historiography, he is credited with issuing the Croeseid, the first true gold coins with a standardised purity for general circulation. And the world's first bimetallic monetary system circa 550 BCE. Herodotus mentioned the innovation made by the Lydians: "So far as we have any knowledge, they were the first people to introduce the use of gold and silver coins, the first who sold goods by retail" Coins spread in the 6th and 5th centuries BC, leading to the development of Ancient Greek coinage and Achaemenid coinage, further to Illyrian coinage. Standardized Roman currency
Popocatépetl is an active stratovolcano, located in the states of Puebla and Morelos, in central Mexico, lies in the eastern half of the Trans-Mexican volcanic belt. At 5,426 m it is the second highest peak in Mexico, after Citlaltépetl at 5,636 m, it is linked to the Iztaccihuatl volcano to the north by the high saddle known as the Paso de Cortés. Popocatépetl is 70 km southeast of Mexico City, from where it can be seen depending on atmospheric conditions; until the volcano was one of three tall peaks in Mexico to contain glaciers, the others being Iztaccihuatl and Pico de Orizaba. In the 1990s, the glaciers such as Glaciar Norte decreased in size due to warmer temperatures but due to increased volcanic activity. By early 2001, Popocatépetl's glaciers were gone. Lava erupting from Popocatépetl has been predominantly andesitic, but it has erupted large volumes of dacite. Magma produced in the current cycle of activity tends to be a mixture of the two; the name Popocatépetl comes from the Nahuatl words popōca "it smokes" and tepētl "mountain", meaning Smoking Mountain.
The volcano is referred to by Mexicans as El Popo. The alternate nickname Don Goyo comes from the mountain's association in the lore of the region with, "Goyo" being a nickname-like short form of Gregorio; the stratovolcano contains a steep-walled, 400 m × 600 m wide crater. The symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris avalanche deposits covering broad areas south of the volcano; the modern volcano was constructed to the south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 AD, have occurred from Popocatépetl since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. According to paleomagnetic studies, the volcano is about 730,000 years old, it is cone shaped with a diameter of 25 km with a peak elevation of 5,450 m.
The crater is elliptical with an orientation northeast-southwest. The walls of the crater vary from 600 to 840 m in height. Popocatépetl is active after being dormant for about half of last century, its activity increased in 1991 and smoke has been seen emanating from the crater since 1993. The volcano is monitored by the Deep Earth Carbon Degassing Project; the geological history of Popocatépetl began with the formation of the ancestral volcano Nexpayantla. About 200,000 years ago, Nexpayantly collapsed in an eruption, leaving a caldera, in which the next volcano, known as El Fraile, began to form. Another eruption about 50,000 years ago caused that to collapse, Popocatépetl rose from that. Around 23,000 years ago, a lateral eruption destroyed the volcano's ancient cone and created an avalanche that reached up to 70 kilometres from the summit; the debris field from, one of four around the volcano, it is the youngest. Three Plinian eruptions are known to have taken place: 3,000 years ago, 2,150 years ago, 1,100 years ago.
The latter two buried the nearby village of Tetimpa. The first known ascent of the volcano was made by an expedition led by Diego de Ordaz in 1519; the early-16th-century monasteries on the slopes of the mountain are a World Heritage Site. Popocatépetl is one of the most active volcanoes in Mexico and the most famous, having had more than 15 major eruptions since the arrival of the Spanish in 1519. Timeline: Mid-to late first century: A violent VEI-6 eruption may have caused the large migrations that settled Teotihuacan, according to DNA analysis of teeth and bones. Eruptions were observed in 1363, 1509, 1512, 1519–1528, 1530, 1539, 1540, 1548, 1562–1570, 1571, 1592, 1642, 1663, 1664, 1665, 1697, 1720, 1802, 1919, 1923, 1925, 1933. 1947: A major eruption. 21 December 1994: The volcano spewed gas and ash, carried as far as 25 km away by prevailing winds. The activity prompted the evacuation of nearby towns and scientists to begin monitoring for an eruption. December 2000: Tens of thousands of people were evacuated by the government, based on the warnings of scientists.
The volcano made its largest display in 1,200 years. 25 December 2005: The volcano's crater produced an explosion which ejected a large column of smoke and ash about 3 km into the atmosphere and expulsion of lava. January and February 2012: Scientists observed increased volcanic activity at Popocatépetl. On January 25, 2012, an ash explosion occurred on the mountain, causing much dust and ash to contaminate the atmosphere around it. 15 April 2012: Reports of superheated rock fragments being hurled into the air by the volcano. Ash and water vapor plumes were reported 15 times over 24 hours. Wednesday 8 May 2013, at 7:28 p.m. local time: Popocatépetl erupted again with a high amplitude tremor that lasted and was recorded for 3.5 hours. It began with plumes of ash that rose 3 km into the air and began drifting west at first, but began to drift east-southeast, covering areas of the villages of San Juan Tianguismanalco, San Pedro Benito Juárez and the City of Puebla in smoke and ash. Explosions from the
Angel of Independence
The Angel of Independence, most known by the shortened name El Ángel and known as Monumento a la Independencia, is a victory column on a roundabout on the major thoroughfare of Paseo de la Reforma in downtown Mexico City. El Ángel was built in 1910 during the presidency of Porfirio Díaz by architect Antonio Rivas Mercado, to commemorate the centennial of the beginning of Mexico's War of Independence. In years it was made into a mausoleum for the most important heroes of that war, it is one of the most recognizable landmarks in Mexico City, it has become a focal point for both celebration or protest. It resembles the Berlin Victory Column in Berlin; the base of the column is quadrangular with each vertex featuring a bronze sculpture symbolizing law, war and peace. There were nine steps leading to the base, but due to the sinking of the ground, an ongoing problem in Mexico City, fourteen more steps were added. On the main face of the base facing downtown Mexico City, there is an inscription reading La Nación a los Héroes de la Independencia.
In front of this inscription is a bronze statue of a giant, laureled lion that guides a child, which symbolizes, according to Rivas Mercado, "the Mexican people, strong during War and docile during Peace."Next to the column there is a group of marble statues of some of the heroes of the War of Independence. The column itself is 36 metres high; the structure is made of steel covered with quarried stone decorated with garlands and rings with the names of Independence figures. Inside the column is a two-hundred step staircase which leads to a viewpoint above the capital; the Corinthian-style capital is adorned by four eagles with extended wings from the Mexican coat of arms used at the time. Crowning the column there is a 6.7 metres statue by Enrique Alciati of Nike, the Greek goddess of Victory, like other similar victory columns around the world. It is covered with 24k gold and weighs seven tons. In her right hand the Angel, as it is known, holds a laurel crown above Miguel Hidalgo's head, symbolizing Victory, while in her left she holds a broken chain, symbolizing Freedom.
Construction of El Ángel was ordered in 1900 by President Porfirio Díaz. Antonio Rivas Mercado began the foundation work and laid the foundation stone on January 2, 1902 and placed in it a gold chest with a record of independence and a series of coins minted in that epoch, but in May 1906, when the foundations were built and 2,400 stones placed to a height of 25 m, the sides of the monument collapsed, so Díaz created a study commission composed of engineers Guillermo Beltran y Puga, Manuel Marroquín y Rivera and Gonzalo Garita. The commission determined that the foundations of the monument were poorly planned, so it was decided to demolish the structure; the work was restarted under the supervision of a steering committee composed of engineers Guillermo Beltran y Puga, Manuel Marroquin y Rivera and the architect Manuel Gorozpe, leaving the artwork in the care of architect Antonio Rivas Mercado. All the sculptures were made by Italian artist Enrique Alciati. One of the faces in the doors is of one of Antonieta.
The monument was completed in time for the festivities to commemorate the first hundred years of Mexican Independence in 1910. The opening ceremony was attended by several foreign dignitaries; the main speaker at the event was Mexican poet Salvador Díaz Mirón. An eternal flame honoring these heroes was installed in the base of the column at the order of President Emilio Portes Gil in 1929; the monument suffered some damage during an earthquake on July 28, 1957 when the sculpture of the Winged Victory fell to the ground and broke into several pieces. Sculptor José Fernández Urbina was in charge of the restoration; the monument was reopened on September 16, 1958. It survived the devastating earthquake of September 19, 1985 with some damage to the staircases and the reliefs, but none to the Angel. In 1925, during the administration of Plutarco Elías Calles, the remains of the following Heroes of the Mexican Independence were interred in a mausoleum under the base of the monument. At the entry to the mausoleum is a statue of William Lamport known as Don Guillén de Lampart y Guzmán, an Irishman, tried by the Mexican Inquisition in the mid seventeenth century, following the discovery of his plot to achieve the independence of New Spain.
He was released by the inquisition to secular authorities and executed in the auto de fe of 1659, with his remains forbidden burial in sacred ground. The actual remains of insurgents are buried in the mausoleum: Father Miguel Hidalgo y Costilla: Chief instigator of independence in 1810 and "Father of the Nation". Father José María Morelos y Pavón: Skilled general and leader of the independence movement after Hidalgo's execution. Ignacio Allende: Lieutenant general of the insurgent army and rebel leader. Juan Aldama: A rebel captain and conspirator. José Mariano Jiménez: Hidalgo's lieutenant colonel. Guadalupe Victoria: Commander of the insurgent army and first President of Mexico. Vicente Guerrero: Insurgent general following the death of Morelos and second President of Mexico. Nicolás Bravo: Commander of the rebel army and President of Mexico on three occasions. Mariano Matamoros: A priest who served as Morelos's lieutenant general. Andrés Quintana Roo: A prominent constitutionalist. Leona Vicario: Active supporter of the rebel movement and wife of Andrés Quintana Roo.
Francisco Javier Mina: A Spanish officer who joined the rebel cause against the absolute monarchy of Ferdinand VII. Pedro
Silver coins are the oldest mass-produced form of coinage. Silver has been used as a coinage metal since the times of the Greeks; the ancient Persians used silver coins between 612-330 BC. Before 1797, British pennies were made of silver; as with all collectible coins, many factors determine the value of a silver coin, such as its rarity, demand and the number minted. Ancient silver coins coveted by collectors include the Denarius and Miliarense, while more recent collectible silver coins include the Morgan Dollar and the Spanish Milled Dollar. Other than collector's silver coins, silver bullion coins are popular among people who desire a "hedge" against currency inflation or store of value. Silver has an international currency symbol of XAG under ISO 4217; the earliest coins in the world were minted in the kingdom of Lydia in Asia Minor around 600 BC. The coins of Lydia were made of electrum, a occurring alloy of gold and silver, available within the territory of Lydia; the concept of coinage, i.e. stamped lumps of metal of a specified weight spread to adjacent regions, such as Aegina.
In these neighbouring regions, inhabited by Greeks, coins were made of silver. As Greek merchants traded with Greek communities throughout the Mediterranean Sea, the Greek coinage concept soon spread through trade to the entire Mediterranean region; these early Greek silver coins were denominated in its fractions. More or less with the development of the Lydian and Greek coinages, a coinage system was developed independently in China; the Chinese coins, were a different concept and they were made of bronze. In the Mediterranean region, the silver and other precious metal coins were supplemented with local bronze coinages, that served as small change, useful for transactions where small sums were involved; the coins of the Greeks were issued by a great number of city states, each coin carried an indication of its place of origin. The coinage systems were not the same from one place to another. However, the so-called Attic standard, Corinthian standard, Aiginetic standard and other standards defined the proper weight of each coin.
Each of these standards were used in multiple places throughout the Mediterranean region. In the 4th century BC, the Kingdom of Macedonia came to dominate the Greek world; the most powerful of their kings, Alexander the Great launched an attack on the Kingdom of Persia and conquering it. Alexander's Empire fell apart after his death in 323 BC, the eastern mediterranean region and western Asia were divided into a small number of kingdoms, replacing the city state as the principal unit of Greek government. Greek coins were now issued by kings, only to a lesser extent by cities. Greek rulers were now minting coins as far away as central Asia; the tetradrachm was a popular coin throughout the region. This era is referred to as the hellenistic era. While much of the Greek world was being transformed into monarchies, the Romans were expanding their control throughout the Italian Peninsula; the Romans minted their first coins during the early 3rd century BC. The earliest coins were - like other coins in the region - silver drachms with a supplementary bronze coinage.
They reverted to the silver denarius as their principal coin. The denarius remained an important Roman coin. During the 3rd century AD, the antoninianus was minted in quantity; this was a "silver" coin with low silver content, but developed through stages of debasement to pure bronze coins. Although many regions ruled by Hellenistic monarchs were brought under Roman control, this did not lead to a unitary monetary system throughout the Mediterranean region. Local coinage traditions in the eastern regions prevailed, while the denarius dominated the western regions; the local Greek coinages are known as Greek Imperial coins. Apart from the Greeks and the Romans other peoples in the Mediterranean region issued coins; these include the Phoenicians, the Carthaginians, the Jews, the Celts and various regions in the Iberian Peninsula and the Arab Peninsula. In regions to the East of the Roman Empire, that were controlled by the Hellenistic Seleucids, the Parthians created a kingdom in Persia; the Parthians issued a stable series of silver drachms and tetradrachms.
After the Parthians were overthrown by the Sassanians in 226 AD, the new dynasty of Persia began the minting of their distinct thin, spread fabric silver drachms, that became a staple of their empire right up to the Arab conquest in the 7th century AD. In the Byzantine Empire, what was left of the eastern Roman Empire, the currency system was reorganised, but the coinage consisted of copper and gold. A silver miliaresion was developed with a cross on steps obverse and an inscription forming the reverse; the cup-shaped trachy were issued, but the silver content of these declined towards only a few per cent ending up as a pure copper coin after the Fourth Crusade. Muhammad established the Constitution of Medina in 622 in the Arabian Peninsula. After the death of Mohammed in 632, the state was governed by caliphs, thus named'the Caliphate'; as the caliphate expanded into Byzantine territories to the Northwest and conquered the Sassanian Empire to the Northeast, the question of a caliphal coinage became imminent.
The caliphate adapted the Sassanian drachm as their silver coin. Arabic inscriptions were added to the Sassanian coin type; the type was c
Iztaccíhuatl, is a 5,230 m dormant volcanic mountain in Mexico located on the border between the State of Mexico and Puebla. It is the nation's third highest, after Popocatépetl 5,426 m; the name "Iztaccíhuatl" is Nahuatl for "White woman", reflecting the four individual snow-capped peaks which depict the head, chest and feet of a sleeping female when seen from east or west. Iztaccíhuatl is to the north of Popocatépetl, to which it is connected by the high altitude Paso de Cortés. Depending on atmospheric conditions Iztaccíhuatl is visible much of the year from Mexico City some 70 km to the northwest; the first recorded ascent was made in 1889, though archaeological evidence suggests the Aztecs and previous cultures climbed it previously. It is the lowest peak containing permanent snow and glaciers in Mexico; the summit ridge of the massive 450 km3 volcano is a series of overlapping cones constructed along a NNW-SSE line to the south of the Pleistocene Llano Grande caldera. There have been andesitic and dacitic Pleistocene and Holocene eruptions from vents at or near the summit.
Areas near the El Pecho summit vent are covered in flows and tuff beds post-dating glaciation 11,000 years ago. The most recent vents are at El Pecho and a depression at 5,100 m along the summit ridge midway between El Pecho and Los Pies. In Aztec mythology, Iztaccíhuatl was a princess who fell in love with one of her father's warriors, Popocatépetl; the emperor sent Popocatépetl to war in Oaxaca, promising him Iztaccíhuatl as his wife when he returned. Iztaccíhuatl was falsely told that Popocatépetl had died in battle, believing the news, she died of grief; when Popocatépetl returned to find his love dead, he took her body to a spot outside Tenochtitlan and kneeled by her grave. The gods changed them into mountains. Iztaccíhuatl's mountain is called "White Woman" because it resembles a woman lying on her back, is covered with snow — the peak is sometimes nicknamed La Mujer Dormida, "The Sleeping Woman". Popocatépetl became an active volcano, raining fire on Earth in blind rage at the loss of his beloved.
Iztaccihuatl is listed at 5,286 m. SRTM data and the Mexican national mapping survey assert that a range of 5,220 to 5,230 m is more accurate; the Global Volcanism Program cites 5,230 m. List of mountain peaks of North America List of mountain peaks of Mexico List of volcanoes in Mexico List of Ultras of Mexico Iztaccíhuatl - Volcano World Iztaccíhuatl - Ski Mountaineer Iztaccíhuatl - Peakware World Mountain Encyclopedia Iztaccíhuatl - Stamps Legend of The Sleeping Lady and Smoking Mountain
Gold is a chemical element with symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright reddish yellow, soft and ductile metal. Chemically, gold is a group 11 element, it is solid under standard conditions. Gold occurs in free elemental form, as nuggets or grains, in rocks, in veins, in alluvial deposits, it occurs in a solid solution series with the native element silver and naturally alloyed with copper and palladium. Less it occurs in minerals as gold compounds with tellurium. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term acid test. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating.
Gold dissolves in mercury, forming amalgam alloys. A rare element, gold is a precious metal, used for coinage and other arts throughout recorded history. In the past, a gold standard was implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, the world gold standard was abandoned for a fiat currency system after 1971. A total of 186,700 tonnes of gold exists above ground, as of 2015; the world consumption of new gold produced is about 50% in jewelry, 40% in investments, 10% in industry. Gold's high malleability, resistance to corrosion and most other chemical reactions, conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices. Gold is used in infrared shielding, colored-glass production, gold leafing, tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine; as of 2017, the world's largest gold producer by far was China with 440 tonnes per year.
Gold is the most malleable of all metals. It can be drawn into a monoatomic wire, stretched about twice before it breaks; such nanowires distort via formation and migration of dislocations and crystal twins without noticeable hardening. A single gram of gold can be beaten into a sheet of 1 square meter, an avoirdupois ounce into 300 square feet. Gold leaf can be beaten thin enough to become semi-transparent; the transmitted light appears greenish blue, because gold reflects yellow and red. Such semi-transparent sheets strongly reflect infrared light, making them useful as infrared shields in visors of heat-resistant suits, in sun-visors for spacesuits. Gold is a good conductor of electricity. Gold has a density of 19.3 g/cm3 identical to that of tungsten at 19.25 g/cm3. By comparison, the density of lead is 11.34 g/cm3, that of the densest element, osmium, is 22.588±0.015 g/cm3. Whereas most metals are gray or silvery white, gold is reddish-yellow; this color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.
Similar effects impart a golden hue to metallic caesium. Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, both may be used to produce police and other badges. White gold alloys can be made with nickel. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. Blue gold can be made by alloying with iron, purple gold can be made by alloying with aluminium. Less addition of manganese, aluminium and other elements can produce more unusual colors of gold for various applications. Colloidal gold, used by electron-microscopists, is red. Gold has only one stable isotope, 197Au, its only occurring isotope, so gold is both a mononuclidic and monoisotopic element. 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. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, β+ decay; the exceptions are 195Au, which decays by electron capture, 196Au, which decays most by electron capture with a minor β− decay path. All of gold's radioisotopes with atomic masses above 197 decay by β− decay. At least 32 nuclear isomers have been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178Au, 180Au, 181Au, 182Au, 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 177m2Au with a half-life of only 7 ns. 184m1Au has three decay paths: β+ decay, isomeric