Element Gold, Au, Transition Metal
History of Gold
|Gold may have been the first known metal used for ornamentation since Neolithic age, 5000 - 4000 years BC. In Egypt, Mesopotamia, India, China and other ancient countries golden ornamentation had been used since 3-2 millennia BC. Gold s mentioned in Bible, and in many masterpieces of ancient literature such as Homer's Iliad and the Odyssey. Alchemists called it "the king of metals"; the symbol for gold was identical with the symbol for the sun. The primary goal of the alchemists was to produce gold from other metals. Gold has been esteemed a precious metal from prehistoric times. The high value placed on it is indicated by the writings of Homer and of Biblical authors. The locality of the ancient sources of supply is now a matter of doubt, but there appear to have been extensive deposits, now probably worked out. |
In the code of Menes, who was King of Egypt about 3600 b.c., the ratio in value between gold and silver is given as 1 part of gold to 2.5 parts of silver. Corresponding with the period about 2500 b.c. there are extant Egyptian rock-carvings illustrating the washing of auriferous sands and the subsequent smelting. The sands were washed over smooth, sloping rocks by running water, and the gold was caught in the hair of raw hides spread on rocks. The " Legend of the Golden Fleece " probably originated in the use of sheepskins for this purpose. It narrates the story of a piratical expedition made about 1200 b.c. with the object of stealing gold obtained from rivers by the aid of sheep or goat skins in the region now termed Armenia.
Chikashige found gold associated with other metals in a Buddhist statue of the third century a.d., and also in a Corean bronze mirror of the tenth century a.d.
The word " gold " is probably derived from the Sanskrit Jvalita, from Jval, meaning to shine.
Gold coins were first made in the Western world about 700 b.c. The parting of gold and silver was then practised, ancient Greek coins containing 99.7 to 99.8 per cent, of gold. The process was one of cementation. At a later period, parting was accomplished by means of nitric acid. At the present time the parting of gold from silver is effected by chlorine in Australia, by electrolysis in America, and by sulphuric acid in Europe.
|Transition Metal Gold is a trace element; its abundance is 4.3x10-7 mass % in crust and less than 5x10-6 mg/l in sea and ocean water. More than 20 gold minerals are known, the most important of which is the native gold (electrum, copper gold, palladium gold, bismuth gold) which is solid solution of silver in gold from trace concentrations to 43% and contains also copper, iron, lead and more rare the metals of platinum group, manganese, bismuth etc. Chemical compounds of gold are very rare in nature and consist mostly of tellurides - calaverite AuTe2, krennerite (Ag, Au)Te2, sylvanite AuAgTe4, petzite Ag3AuTe2, muthmannite (Ag, Au)Te, montbrayite Au2Te3 and others. Gold is also present in quartz, carbonates, pyrite, arsenopyrite, galena, sphalerite and chalcopyrite. Gold is present in ores as inclusions with usual sizes 0.1-1000 µm; however nuggets with weight up to several kilograms also may be found. Genetic types of commercially important deposits include those of hydrothermal high-temperature gold-arsenopyrite formations, hydrothermal medium temperature quartz-sulphide and gold-quartz formations, metamorphized and weathered deposits and alluvial placers.|
The greater part of the world's gold is found in the metallic state either in primary deposits in veins in association with quartz, or as alluvial gold in secondary deposits in the form of dust, grains, fine leaves, or in larger pieces.
In the quartz-veins the metal is found in varying degrees of fine division, and is usually associated with arsenic or sulphur compounds such as iron pyrites, arsenical pyrites, copper pyrites, zinc-blende, galena, antimony-glance, and various silver ores. The metal is frequently present in crystalline form, examples being cubes and octahedra belonging to the cubic system, and also hexagonal forms. The amount of gold in the ore ranges from a few grams per ton up to several hundred grams per ton in different localities, and also varies at different levels in the same locality, diminishing with increase of depth. Such is the value of the metal that 3 ounces of gold per 50 tons of gangue can be profitably worked.
Alluvial gold is a product of the disintegration of gold-bearing rocks, due to weathering by the atmosphere and water. It is present in river-sand and in sand-deposits in all auriferous regions, as well as in districts where quartz-gold formerly occurred. It is usually associated with such materials as quartz-sand, clay, mica, titaniferous iron ore, chrome iron ore. magnetic iron ore, tinstone, granite, spinell, zirconium, platinum, and diamonds. Large pieces, or nuggets, weighing several kilograms are sometimes found.
Combined gold is always found in union with tellurium. Muthmannite contains a considerable proportion of gold, and is represented by the formula (Ag, Au)Te. The molecular proportion of the gold is always less than that of the silver. Other examples of such minerals are sylvanite, with 24.30 per cent, of gold, 3.15 per cent, of silver, and 58.62 per cent, of tellurium, found in Transylvania, California, and Colorado; hessite, or silver telluride, with part of the silver replaced by gold; calaverite, AuTe2, containing a small proportion of silver; petzite, with a large proportion of silver; nagyagite, containing lead, copper, sulphur, tellurium, and antimony; and white tellurium, containing silver, lead, tellurium, and antimony; these ores are found in Transylvania.
Gold is almost always associated with silver and copper. It is found in South Africa, America, Russia, Australia, Hungary, Sweden, and Norway. The cyanide-process has been highly developed in South Africa, and the electrolytic separation from copper in America.