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SILVER |
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Silver is found in native form, alloyed with gold or combined with sulfur, arsenic, antimony or chlorine in ores such as argentite (Ag2S), horn silver (AgCl), and pyrargyrite (Ag3SbS3). The principal sources of silver are the ores of copper, copper-nickel, lead, and lead-zinc.
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Formation of Silver |
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Many of the metals that are so important to us, such as gold, silver, copper, lead, zinc, are present in the Earth’s crust only in very small amounts. Silver is present as only about 5 parts in a million.
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Apart from gold, which is special, the other metals form compounds with sulphur, called sulphides. Deep in the Earth’s crust, where it is very hot, salty water (called brine) circulates and dissolves these metals, collecting them up and concentrating them in the hot brine. The brine can be as hot as 350°C. Sometimes, on the sea floor, this brine comes up through the surface out of holes we call vents. When the hot brine comes into contact with the cold sea water the metal sulphides cannot stay dissolved and precipitate onto the sea floor as various minerals. Copper is precipitated as chalcopyrite (copper sulphide), lead as galena (lead sulphide), and zinc as sphalerite (zinc sulphide). Silver precipitates as a mixture with the other sulphides. The sulphides build up on the seafloor around the vents, like chimneys. Because the water appears black with all the minerals in it, the chimneys are called Black Smokers.
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Properties of Silver |
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Silver has many special properties that make it a very useful and precious metal. It has an attractive shiny appearance, although it tarnishes easily. The tarnish is silver sulphide and it forms as the silver reacts with sulphur compounds in the atmosphere. Of all the metals, silver is the best conductor of heat and electricity known, in fact it has the highest electrical and thermal conductivity known for any material. It is strong, malleable and ductile, and can endure extreme temperature ranges. Silver is also able to reflect light very well.
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| The Properties of Silver |
| Chemical Symbol: |
Ag |
| Relative density: |
10.5 |
| Hardness: |
3.25 on Mohs scale |
| Malleability: |
High |
| Ductility: |
High |
| Electrical conductivity: |
Highest known |
| Thermal conductivity: |
Highest known |
| Melting point: |
961.93°C |
| Boiling point: |
2212°C |
| Atomic Mass: |
107.87 |
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Silver in India |
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In India, there are no native silver deposits except the small and unique Bharak deposit of silver in Rajasthan. This mineral occurs as an associate with most of copper and lead-zinc minerals. The important deposits where this mineral occurs are Zawar group, Dariba group, Bamina Kalan, Sindesar Khurd, Rampura Agucha, Sargipalli, Bandalamottu, Ghugra, etc. Silver is recovered as coproduct from Hutti Gold mines in Karnataka during refining of Gold and at Vizag Zinc smelter, Andhra Pradesh from lead concentrates.
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