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Silver

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Silver is an element with the chemical symbol Ag and atomic number 47. Opaque and bright silvery white with a slightly pink tint, it readily tarnishes to either gray or black. Natural crystals of silver are uncommon, but when found they are cubic, octahedral, or dodecahedral. It is usually found in granular habit and as wiry, branching, lamellar, or scaly masses. Widely distributed in nature, it is a primary hydrothermal mineral. It also forms by alteration of other silver-bearing minerals. Much of the world’s silver production is a by-product of refining lead, copper, and zinc. It is the second most malleable and ductile metal, and it is important in the photographic and electronic industries. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. It has long been valued as a precious metal. Silver metal is used in many bullion coins, sometimes alongside gold: while it is more abundant than gold, it is much less abundant as a native metal.

Name: From an Old English word for the metal soelfer, related to the German silber and the Dutch zilver; the chemical symbol from the Latin argentum

Association: Acanthite, chlorargyrite, embolite, silver sulfosalts, gold, copper

Polymorphism & Series: Forms a series with gold; the cubic form is 3C; hexagonal stacking polytypes 2H and 4H are known

Mineral Group: Copper Group

Cell Data: Space Group: Fm3m. a = 4.0862 Z = 4

Morphology: Crystals are cubic, octahedral, dodecahedral to a cm. Often elongated to many cms in herringbone twins and wires (crystals elongated along the [111] axis).

Chemical Properties

Chemical Classification Native – members of Copper Group
Formula Ag
Common Impurities Au,Hg,Cu,Sb,Bi

Silver’s Physical Properties

Color Silver-white, tarnishes dark gray to black
Streak Silver white
Luster Metallic
Cleavage None Observed
Diaphaneity Opaque
Mohs Hardness 2.5-3 on Mohs scale
Crystal System Isometric
Tenacity Malleable
Density 10.1 – 11.1 g/cm3 (Measured)    10.497 g/cm3 (Calculated)
Fracture None observed

It is an extremely soft, ductile and malleable transition metal, though it is slightly less malleable than gold. Crystallizes in a face-centered cubic lattice with bulk coordination number 12, where only the single 5s electron is delocalized, similarly to copper and gold.

It has a brilliant white metallic luster that can take a high polish, and which is so characteristic that the name of the metal itself has become a color name.

Very high electrical and thermal conductivity is common to the elements in group 11, because their single s electron is free and does not interact with the filled d subshell, as such interactions (which occur in the preceding transition metals) lower electron mobility. The electrical conductivity of it is the greatest of all metals, greater even than copper, but it is not widely used for this property because of the higher cost. An exception is in radio-frequency engineering, particularly at VHF and higher frequencies where silver plating improves electrical conductivity because those currents tend to flow on the surface of conductors rather than through the interior.

Silver Optical Properties

Type Isotropic
Color / Pleochroism Non-pleochroic
Color in reflected light Brilliant silver white
Internal Reflections None
Twinning Penetration twins on (111) with cubes from Kongsberg and tetrahexahedrons from Michigan (bearpaws). Arborescent growths twinned on (100) and on (111).

Silver Occurrence

A primary hydrothermal mineral, also formed by secondary processes, especially in the oxidized portions of mineral deposits.

The abundance of silver in the Earth’s crust is 0.08 parts per million, almost exactly the same as that of mercury. It mostly occurs in sulfide ores, especially acanthite and argentite, Ag2S. Argentite deposits sometimes also contain native when they occur in reducing environments, and when in contact with salt water they are converted to chlorargyrite (including horn silver), AgCl, which is prevalent in Chile and New South Wales. Most other this minerals are pnictides or chalcogenides; they are generally lustrous semiconductors. Most true silver deposits, as opposed to argentiferous deposits of other metals, came from Tertiary period vulcanism.

It is usually found in nature combined with other metals, or in minerals that contain silver compounds, generally in the form of sulfides such as galena (lead sulfide) or cerussite (lead carbonate). So the primary production of requires the smelting and then cupellation of argentiferous lead ores, a historically important process. Lead melts at 327 °C, lead oxide at 888 °C and silver melts at 960 °C. To separate the silver, the alloy is melted again at the high temperature of 960 °C to 1000 °C in an oxidizing environment. The lead oxidises to lead monoxide, then known as litharge, which captures the oxygen from the other metals present. The liquid lead oxide is removed or absorbed by capillary action into the hearth linings.

Silver Uses Area

The earliest known coins were minted in the kingdom of Lydia in Asia Minor around 600 BC. The coins of Lydia were made of electrum, which is a naturally occurring alloy of gold and silver, which available within the territory of Lydia. Since that time, standards, in which the standard economic unit of account is a fixed weight of silver, have been widespread throughout the world until the 20th century.

Today, silver bullion has the ISO 4217 currency code XAG, one of only four precious metals to have one (the others being palladium, platinum, and gold).

Applications

The major use of silver besides coinage throughout most of history was in the manufacture of jewellery and other general-use items, and this continues to be a major use today.

Electrolytically refined pure silver plating is effective at increasing resistance to tarnishing.

Wound dressings containing silver sulfadiazine or silver nanomaterials are used to treat external infections. It is also used in some medical applications, such as urinary catheters (where tentative evidence indicates it reduces catheter-related urinary tract infections) and in endotracheal breathing tubes (where evidence suggests it reduces ventilator-associated pneumonia).

It and its nanoparticles are used as an antimicrobial in a variety of industrial, healthcare, and domestic application: for example, infusing clothing with nanosilver particles thus allows them to stay odourless for longer

Silver and its alloys are used in cranial surgery to replace bone, and silver–tin–mercury amalgams are used in dentistry.

Silver diammine fluoride, the fluoride salt of a coordination complex with the formula [Ag(NH3)2]F, is a topical medicament (drug) used to treat and prevent dental caries (cavities) and relieve dentinal hypersensitivity.

It is very important in electronics for conductors and electrodes on account of its high electrical conductivity even when tarnished. Bulk silver and silver foils were used to make vacuum tubes, and continue to be used today in the manufacture of semiconductor devices, circuits, and their components.

Containing brazing alloys are used for brazing metallic materials, mostly cobalt, nickel, and copper-based alloys, tool steels, and precious metals.

Equipment made to work at high temperatures is often silver-plated. It and its alloys with gold are used as wire or ring seals for oxygen compressors and vacuum equipment.

The photosensitivity of the silver halides allowed for their use in traditional photography, although digital photography, which does not use silver, is now dominant.

Pure silver metal is used as a food colouring. It has the E174 designation and is approved in the European Union.

Distribution

Numerous localities even for fine specimens. Well-crystallized examples from:

  • in Germany, near Freiberg and Marienberg, Saxony, and at St. Andreasberg, Harz Mountains.
  • Exceptionally developed at Kongsberg, Norway.
  • From Prıbram and Jachymov (Joachimsthal), Czech Republic.
  • In Italy, from Monte Narba, Sarrabus, Sardinia.
  • In the USA, on the Keweenaw Peninsula, Houghton and Keweenaw Cos., Michigan; at Aspen, Pitkin Co., and from Creede, Mineral Co., Colorado; and in Arizona, in the Silver King mine, Pinal Co. In Canada, in large amounts from Cobalt; and in the Thunder Bay district, at Silver Islet, on the north shore of Lake Superior, Ontario. Important production from Mexico, in many states; finely crystallized from Batopilas, Chihuahua; masses over 1500 kg from Arizonac, Sonora.
  • At Chanarcillo, south of Copiapo, Atacama, Chile.
  • In Australia, at Broken Hill, New South Wales.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Orpiment: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].
  • Wikipedia contributors. (2019, June 7). Silver. In Wikipedia, The Free Encyclopedia. Retrieved 14:35, June 10, 2019, from https://en.wikipedia.org/w/index.php?title=Silver&oldid=900845751
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