Gold
Cultural history
The Turin Papyrus Map
Funerary mask of Tutankhamun
Jason returns with the golden fleece on an Apulian red-figure calyx krater, ca. 340– 330 BC.
Gold artifacts found at the Nahal Kana cave cemetery dated during the 1980s, showed these to be from within the Chalcolithic, and considered the earliest find from the Levant (Gopher et al. 1990). Gold artifacts in the Balkans also appear from the 4th millennium BC, such as those found in the Varna Necropolis near Lake Varna in Bulgaria, thought by one source (La Niece 2009) to be the earliest "well-dated" find of gold artifacts. 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. 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. 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.[60] 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[61]
The Portuguese overseas expansion started in 1415 with the taking of Ceuta, to control the gold trade coming across the desert. Although the caravan trade routes were then diverted, the Portuguese continued expansing southwards along the coast and eventually buying the gold directly (or less indirectly) from the Africans in the Gulf of Guinea.[citation needed] 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).[62] 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.[63] 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 was not to check if the coin was gold (90% gold coins are fairly strong) but to see if the coin was gold plated lead. A lead coin would be very soft and thus teeth marks would result. Fake gold coins were a common problem before 1932 so weighing a coin and also sliding a coin through a "counterfeit detector" slot was common (making a lead coin thicker would add weight thus why slide it through a measured slot). Most establishments (especially US Western saloons) would never accept a gold (or silver) coin of high value before weighing such an item.[citation needed] Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.[64] It has been estimated that all gold ever refined would form a single cube 20 m (66 ft) on a side (equivalent to 8,000 m3).[64] 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 the philosopher's stone. 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. Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another Atomic Number: 79 Symbol: Au Atomic Weight: 196.9665
Discovery: known since prehistoric time Electron Configuration: [Xe]6s14f145d10 Word Origin: Sanskrit Jval; Anglo-Saxon gold; meaning gold - also Latin aurum, shining dawn Isotopes: There are 36 known isotopes of gold ranging from Au-170 to Au-205. There is only one stable isotope of gold: Au-197. Gold-198, with a half-life of 2.7 days, has been used to treat cancer and other illnesses. Density (g/cc): 19.3 Melting Point (°K): 1337.58 Boiling Point (°K): 3080 Appearance: soft, malleable, yellow metal Atomic Radius (pm): 146 Atomic Volume (cc/mol): 10.2 Covalent Radius (pm): 134 Ionic Radius: 85 (+3e) 137 (+1e) Specific Heat (@20°C J/g mol): 0.129 Fusion Heat (kJ/mol): 12.68 Evaporation Heat (kJ/mol): ~340 Debye Temperature (°K): 170.00 Pauling Negativity Number: 2.54 First Ionizing Energy (kJ/mol): 889.3 Oxidation States: 3, 1. The oxidation states -1, +2 and +5 exist but are rare. Lattice Structure: Face-Centered Cubic (FCC) Lattice Constant (Å): 4.080 Specific Gravity (20°C): 18.88
CAS Registry Number: 7440-57-5 Properties: In mass, gold is a yellow-colored metal, although it may be black, ruby, or purple when finely divided. Gold is a good conductor of electricity and heat. It is not affected by exposure to air or to most reagents. It is inert and a good reflector of infrared radiation. Gold is usually alloyed to increase its strength. Pure gold is measured in troy weight, but when gold is alloyed with other metals the term karat is used to express the amount of gold present. Uses: Gold is used in coinage and is the standard for many monetary systems. Gold is used for jewelry, dental work, plating, and reflectors. Chlorauric acid (HAuCl4) is used in photography for toning silver images. Disodium aurothiomalate, administered intramuscularly, is a treatment for arthritis. Sources: Gold is found as the free metal and in tellurides. It is widely distributed and almost always associated with pyrite or quartz. Gold is found in veins and in alluvial deposits. Gold occurs in sea water in the amount of 0.1 to 2 mg/ton, depending on the location of the sample. Production 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.[73][74] 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 Gold Trivia: • •
Gold is one of the few elements that can be found in its native state. Gold is the most malleable and ductile metal. One ounce of gold can be beaten out to 300 ft2 or stretched into a wire 2000 kilometers long (1 μm thick).
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The melting point of gold is an assigned value, which serves as a calibration point for the International Temperature Scale and International Practical Temperature Scale.
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The gold ion in the +1 oxidation state (Au(I)+) is called the aurous ion.
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The gold ion in the +3 oxidation state (Au(III)3+) is called the auric ion.
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Compounds containing gold in the -1 oxidation state are called aurides. (Cesium and rubidium can form auride compounds)
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Gold is one of the noble metals. Noble metal is an alchemical term for metals that do not corrode under normal conditions.
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Gold is the seventh most dense metal.
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Gold has been used as jewelry since prehistoric times. Today, gold in jewelry is not 'pure' gold. Jewelry gold is made of many different gold alloys.
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Gold is resistant to most acids. The acid aqua regia is used to dissolve gold.
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Elemental gold metal is considered non-toxic and occasionally used as a food additive.
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Transmuting lead into gold was one of the major gold of the alchemists. Modern nuclear chemists have found methods to accomplish this historic task.
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952) International Atomic Energy Agency ENSDF database (Oct 2010) Return to the Periodic Table of the Elements New posts to the Chemistry forums: • •
Biochemistry how to protect mylar?
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Scientific Subject
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History & Etymology • The elements Copper, Silver, and Gold are collectively known as the "coinage metals" because of their former usage. These elements were almost certainly the first three metals known to man. All of them occur in the elemental, or "native", form and must have been used as primitive money long before the introduction of gold coins in Egypt around 3400 BC.
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Cold-hammering was used in the late Stone Age to produce plates of gold for ornamental purposes, and this metal has always been synonymous with beauty, wealth and power. Gold ornaments of great variety and elaborate workmanship have been discovered on sites belonging to the earliest known civilizations; Minoan, Egyptian, Assyrian, Etruscan, and in ancient literature Gold is the universal symbol of the highest purity and value. Cf. passages in the Old Testament, e.g. Ps. xix, 10:
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"More to be desired are they than gold, yea, than much fine gold."
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Some of the early rich finds of gold artifacts were from the cemeteries in Bulgaria in Europe (5th millennium BC) with accouterments of hammered and sheet gold. Some of the most elegant gold vessels made by the repousse technique come from the Mesopotamia (ca 2500 BC). The Babylonian name for gold - hurasu has a distant resemblance to the Ancient Greek word Χρυσος [chrysos], which is found in the earliest texts. Possibly, this word originates from the name of the place where Gold was found. Spectacular gold castings are known from ancient Egypt, such as the coffin of
Tutankhamun (a minor Pharaoh who was only 18 when he died), which contained no less than 112 kg of gold. The Gold mines of Egypt were in Nubia. Hence the ancient Egyptian name for gold - nub. Early gold and silver ornaments from the Indian subcontinent are found from Indus Valley sites such as Mohenjodaro (ca 3000 BC). The ancient Indian word ayas for Gold was later used in other languages for the designation of copper, which, possibly, serves as indication of propagation in the antiquity of false gold. • The legendary Aztec and Inca hoards in Mexico and Peru were a major reason for the Spanish conquests of Central and South America in the early sixteenth century. •
From the earliest times gold was compared with the sun, it was called the solar metal or simply by the sun (Sol). The alchemist symbol for gold - a circle with a dot in the center, is identical with the symbol for the sun. In the alchemic literature gold was indicated with many words, usually encoded, such as: zaras, trikor, sol, sonir, secur, senior, etc., and also several words with an Arab origin, for example al-bahag (gladness), hiti (cat dung), ras (head, principle), su'a (ray), diya (light), and alam (peace).
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In astrology alchemy the seven heavenly bodies known to the ancients were associated with seven metals also known in antiquity: Sun (Sol)
Gold (Aurum)
Mercury (Mercurius) Mercury (Hydrargyrum)
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Venus
Copper (Cuprum)
Moon (Luna)
Silver (Argentum)
Mars
Iron (Ferrum)
Jupiter
Tin (Stannum)
Saturn Lead (Plumbum) The long history of Gold is reflected in the many different words for this metal, although many names seem to mean originally "yellow (metal)". See the list of names to the left and in the overview of Gold in over 100 languages (click here). We can identify many diffent roots, even the three main European branches of the IndoEuropean language group have different roots for their name of this common metal: aurum, the Germanic gold and the Slavic золото (zoloto). 1. Aurum (Italic branch) The Latin (Etruscan) name aurum (ancient ausom) means "yellow". This word is compared well with the the ancient-roman aurora or ausosa (the morning glow, the
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eastern country, the east). The word is also derived from a Sanskrit word "hari", meaning "yellow". Most of the Roman languages and the Celtic languages use derivations of aurum. 2. Gold (Germanic branch) The Germanic word gold was already used in the old "Germanic" languages, some of the modern languages use a derivation of it (as goud in Dutch). The root of gold is *gelwa, yellow, which came from Sanskrit "jval", to shine. Literally gold means "the yellow, shining metal". Also the Finnish and Estonian words seems to be derivations of "gold". The Latvian words means yellow too. 3. Золото (zoloto) (Slavic branch) The Slavic languages use different forms of золото, zlato. This word, used from the earliest times, is undoubtedly is connected with the earliest Indo-European Sol (sun). 4. Altın (Altaic languages) 5. Dhahab, zahav (Afro-Asiatic languages) 6. Amalãmã (Aromanian) This word comes from Greek "malagma", (Medieval Latin amalgama), soft mass. (information by Prof. Emil Vrabie). Reaksi Kimia Unsur
Tingginya nilai potensial reduksi emas mengakibatkan logam ini selalu terdapat di alam dalam keadaan bebas. Untuk keperluan ektraksi dari bijihnya, proses dengan melibatkan senyawa sianida dapat diterapkan seperti halnya pada ekstraksi logam perak. Emas membentuk berbagai senyawa kompleks, tetapi hanya sedikit senyawa anorganik sederhana. Emas (I) oksida, Au2O, adalah salah satu senyawa yang stabil dengan tingkat oksidasi +1, seperti halnya tembaga, tingkat oksidasi +1 ini hanya stabil dalam senyawa padatan, karena semua larutan garam emas (I) mengalami disproporsionasi menjadi logam emas dan ion emas (III) menurut persamaan reaksi : 3Au+(aq) → 2Au(s) + Au3+(aq) Secara kimiawi emas tergolong inert sehingga disebut logam mulia. Emas tidak bereaksi dengan oksigen dan tidak terkorosi di udara di bawah kondisi normal. Namun emas terurai dalam larutan sianida dalam tekanan udara. Emas juga tidak bereaksi dengan asam atau basa apapun. Akan tetapi emas bereaksi dengan halogen dan aqua regia. Reaksi emas dengan halogen Logam emas bereaksi dengan klorin, Cl2, atau bromin, Br2, untuk membentuk trihalida emas (III) klorida, AuCl3, atau emas (III) bromida, AuBr3. 2Au(s) + 3Cl2(g) → 2AuCl3(s) 2Au(s) + 3Br2(g) → 2AuBr3(s) AuCl3 dapat larut dalam asam hidroksida pekat menghasilkan ion tetrakloroaurat (III), [AuCl4]-, suatu ion yang merupakan salah satu komponen dalam “emas cair”, yaitu suatu campuran spesies emas dalam larutan yang akan mengendapkan suatu film logam emas jika dipanaskan.
Di lain pihak, logam emas bereaksi dengan iodin, I2, untuk membentuk monohalida, emas (I) iodida, AuI. 2Au(s) + I2(g) → 2AuI(s) Emas dapat larut pada aqua regia, yaitu campuran tiga bagian volum asam klorida pekat dan atau bagian volum asam nitrat pekat ( Jabir ibn-Hayyan, ca. 760-815 ) : Au(s) + 4HCL (aq) + HNO3(aq) → HAuCl4(aq) + NO (g) + 2H2O(l) Sejarah Emas Emas ( Sanskrit jval, Yunani χρυσος = chrysos, Latin aurum, berarti fajar yang cerah, AngloSaxon gold, China 金 [jīn], Jepang 金 [kin] ) telah diketahui sebagai sangat berharga sejak zaman prasejarah. Emas, merupakan salah satu logam tertua yang digunakan oleh manusia. Emas dikenal antara lain di Mesopotamia dan Mesir. Referensi ke awal mula penemuan emas didasari legendaris atau mitos. Oleh karena itu, beberapa penulis menyebutkan bahwa penemu emas pertama kali adalah Cadmus, bangsa Phoenicia. Sedangkan yang lainnya mengatakan bahwa Thoas, raja Taurian, yang pertama kali menemukan logam berharga dalam legenda Pangaeus Mountains di Thrace. Legenda dan mitos serupa tentang awal penemuan emas juga terdapat dalam sastra kuno dari Hindu ( the Vedas ) serta Cina dan bangsa lainnya... Emas dari estetika properti fisik dikombinasikan dengan properti sudah lama menjadi logam yang berharga. Sepanjang sejarah, emas telah sering menjadi penyebab konflik : misalnya ada awal tahun 1500-an Raja Ferdinand dari Spanyol menetapkan prioritas kepada para conquistador – penakluk - hambanya yang akan berangkat mencari Dunia Baru, "Bawa pulanglah emas," perintahnya kepada mereka, "kalau bisa, dapatkan semanusiawi mungkin, tapi apapun risikonya, bawalah emas." Titah sang raja tersebut menjadi awal pemusnahan peradaban Aztec dan Inca. Konflik karena perebutan emas juga terjadi pada awal ketika Amerika berburu emas ke Georgia, California, dan Alaska. Pada abad pertengahan, begitu kuat orang mendambakan emas, sehingga lahir ilmu alkimia, dengan tujuan membuat emas. Manusia modern berhasil mencapai cita-cita itu dengan mengekstrak emas dari air laut dan mengubah timbel atau merkurium menjadi emas dalam mempercepat partikel. Namun emas yang murah tetaplah emas alamiah yang harus ditambang. Biji emas dikategorikan dalam 4 ( empat ) kategori : 1. Biji tipis dimana kandungannya sebesar 0.5 g/1000 kg atau 0.5 g/ton atau 0.5 ppm ( part per million, per satu juta bagian ) 2. Biji rata-rata ( typical ) dengan mudah digali, nilai biji emas khas dalam galian terowongan terbuka yakni kandungan 1-5 g/1000 kg (1 -5 ppm ) 3. Biji bawah tanah/harrdrock dengan kandungan 3 g/1000 kg ( 3 ppm ) 4. Biji nampak mata ( visible ) dengan kandungan minimal 30 g/1000 kg ( 30 ppm )
Kelimpahan relatif emas di dalam kerak bumi diperkirakan sebesar 0,004 g/ton, termasuk sekitar 0,001 g/ton terdapat di dalam perairan laut. Menurut Greenwood dkk (1989), batuan bijih emas yang layak untuk dieksploitasi sebagai industri tambang emas, kandungan emasnya sekitar 25 g/ton (25 ppm). Emas di dunia mulai ditambang sejak tahun 2.000 sebelum masehi oleh bangsabangsa di dataran Mesir ( bangsa Mesir, Sudan dan Arab Saudi ). Pada sekitar abad ke-19, pencarian emas muncul kapanpun ketika ditemukan adanya deposit emas, termasuk di California, Colorado, Otago, Australia, Black Hills, dan Klondike. Sedangkan deposit emas terbesar ditemukan di Precambrian Witwatersrand, Afrika Selatan, dengan luasan ratusan mil dan dengan kedalaman di lebih dari dua mil. Sejak tahun 1880-an, Afrika Selatan telah menjadi sumber untuk sebagian besar sediaan emas dunia. Pada tahun 1970, produksinya mencapai hingga 70 % dari persediaan dunia, yaitu memproduksi sekitar 1000 ton, namun produksi di tahun 2004 hanya 342 ton. Penurunan ini berhubungan dengan bertambahnya kesulitan dalam ektraksi dan faktor ekonomi yang memperngaruhi industri Afrika Selatan. Produsen utama lainnya adalah Kanada, Australia, bekas Uni Soviet, dan Amerika Serikat ( Arizona, Colorado, California, Montana, Nevada, South Dakota, dan Washington ). Sebelum Perang Dunia II, Indonesia adalah penghasil emas terbesar di Asia Tenggara. Satusatunya pengelola tambang emas di Indonesia pada awal tahun 1980-an adalah PT Aneka Tambang, sebuah BUMN di bawah Departemen Pertambangan dan Energi. Tiga penambang emas besar di Indonesia menurut data tahun 1987 adalah: • • •
PT Freeport Indonesia Inc. yang berlokasi di Tembagapura, Papua dengan jumlah produksi 2,2 ton/tahun ( 1986 ). PT Lusang Mining yang berlokasi di Bengkulu dengan jumlah produksi 300 kg/tahun ( 1986 ). PT Aneka Tambang ( Persero ) berlokasi di Cikotok, Jawa Barat dengan jumlah produksi 240 kg/tahun ( 1986 ).
