19 Mart 2013 Salı

Texas State Mineral

Texas State Mineral


Official State Metal of Nevada
The element silver, when freshly exposed to air, is bright and silver-white in color. It eventually tarnishes with exposure to sulfur or sulfides. This tarnished layer of silver sulfide can be black, brown, yellow, or gray. Silver is a member of the copper group and is often found in association with copper. Silver is found pure in the earth as native silver, and frequently has traces of gold, arsenic, and antimony.
Franciscan friars discovered silver in Texas in about 1680, and operated mines near El Paso. Several mines operated throughout the state from the 1880s until 1952, when Texas silver production came to a halt. Mining was briefly renewed in the late 1970s when the price of silver rose. The extensively developed Presidio Mine near Shafter was one of the biggest silver producers in the state and the country. In 2007, the Texas Legislature designated silver the state precious metal. 
Silver was also designated the official metal of Nevada in 1977. 
The word "silver" comes from the Old English word seolfer. "Silver" is also related to the German word silber and the Dutch word zilfer. The Latin word for silver is argentum, which led to the element’s chemical symbol, Ag. An early Latin word for silver was luna, which means "moon", referring to its bright luster. Silver has also been associated with the sea and various lunar goddesses.
Silver is primarily found in hydrothermal veins, and is also formed by secondary processes, especially in the oxidized portions of mineral deposits. In the United States, silver is mostly produced as a byproduct from copper, copper-molybdenum, gold, and lead-zinc ores, although four mines produce silver as a principal product.
Silver is widespread. Only a few localities for fine specimens are listed here.
  • Germany: Freiberg and Marienberg, Saxony; and St. Andreasberg, Harz Mountains
  • Norway: Kongsberg
  • Czech Republic: Příbram and Jáchymov (Joachimsthal)
  • Italy: Monte Narba, Sarrabus, Sardinia
  • United States: Keweenaw Peninsula, Houghton and Keweenaw Counties, Michigan; Aspen, Pitkin County, Colorado; Creede, Mineral County, Colorado; and Silver King mine, Pinal County, Arizona; Nevada
  • Canada: Cobalt, Ontario; and Thunder Bay district, at Silver Islet, on the north shore of Lake Superior, Ontario
  • Mexico: Batopilas, Chihuahua; Arizonac, Sonora; and many other locations
  • Chile: Chañarcillo, south of Copiapó, Atacama
  • Australia: Broken Hill, New South Wales
Silver has been used for decorative purposes since approximately 300 BCE. It was first used for jewelry, decorative items, and mirrors.
Silver is the best conductor of electricity, superior even to copper, and the second most malleable and ductile metal. Today, silver has many applications, including coin and medal fabrication, electrical and electronics components, jewelry, silverware, scientific equipment, musical instruments, and photography. The use of silver in televisions using flat screens has increased recently, and silver use in this application is expected to double in the next few years. The use of silver radio-frequency identification devices, or RFIDs, an alternative to bar codes used by a variety of industries as a way to track stock and shipments, is expected to increase. Antibacterial uses of silver in wound and burn care are increasing. A powder that contains silver clots blood on contact and also prevents growth of bacteria. According to the U.S Geological Survey, the use of silver in electronics, medicine, superconductivity, water purification, and wood preservatives is expected to continue to increase.
The 1804 U.S. silver dollar, composed of 90 percent silver and 10 percent copper, is considered to be one of the world’s rarest and most famous coins. Specimens are among the most sought-after coins due to their interesting history. U.S. silver dollars dated 1804 did not actually appear until 1834, when coins were minted as gifts for the Sultan of Muscat and Oman, and the King of Siam. Coins were minted using old dies in an effort to cut costs. Several specimens of the 1804 silver dollar are on display at the American Numismatic Association Museum in Colorado Springs, Colorado, and two are part of the National Coin Collection held by the Smithsonian Institution. In 2008, one specimen sold at auction for $3.7 million, and in 2009, one was auctioned for $2.3 million.
According to the Giant Crystal Project, the largest silver crystal ever found is about 1.2 inches (3 cm) long and the longest silver crystalline wires are 78.7 inches (2 m) long. Both are on display at the Norsk Bergverksmuseum in Kongsberg, Norway. The largest native silver aggregate is reportedly from the famous silver mining area known as the Silver Sidewalk in Cobalt, Ontario, Canada. A specimen from that location measures approximately 328 feet by 197 feet by 1.3 feet (100 m x 60 m x 0.4 m).
Since pure silver is soft and tarnishes easily, substitutes are important in many applications. Sterling silver, an alloy of 92.5 percent silver and 7.5 percent copper or other metals, is frequently used in jewelry and flatware. Argentium sterling silver contains 7.5 percent germanium, an element that adds higher tarnish resistance, elimination of firescale, increased ductility, and other advantages to the silver alloy. Stainless steel can be used to make flatware and other items. Platinum is harder, heavier, and does not tarnish, but is also more expensive. Digital photography and digital imaging may reduce the demand for silver-based films.
State Mineral
Silver Nuggets
State Mineral
Extracting Silver Ore
State Mineral
Tarnished Silver Platter
State Mineral
Coins Have Been Made of Silver Throughout History
Group: Transition metal
Chemical Formula: Ag
Crystal Structure: Face-centered cubic
Hardness (Mohs): 2½-3
Color: Silver-white, tarnishes dark gray to black
Transparency: Opaque
Luster: Metallic
Density: 10.1-11.1 g/cm3
Streak: Silver white
Cleavage: None Observed
Fracture: None observed
Tenacity: Malleable
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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