Geology Reference
In-Depth Information
in integrated circuits and photovoltaic cells are made of thinly cut slices of simple
silicon crystals.
B.2.59 Silver
Silver is widely distributed in sulphide ores of which argentite (Ag 2 S) is the most
important. It can also be found in its native form in nature and associated with
chlorine as AgCl. Only about 10% of all silver mined is obtained from deposits
primarily exploited for the metal; 90% or more stems from copper, lead, zinc and
gold mining where silver is a byproduct.
In addition to coinage, silver is used mainly in tableware, mirrors, electronic
products, photography, jewellery and as a catalyst in oxidation reactions.
B.2.60 Sodium
Sodium is a white-silvery metal, belonging to the alkali group and is hence highly
reactive. Sodium is a very abundant element in the Earth's crust. After chloride,
sodium is also the second most abundant element dissolved in seawater. Sodium
occurs as rock-salt (NaCl) and in various forms: as a carbonate, nitrate, sulphate,
borate, etc.
Sodium in its metallic form is very important in the making of esters and in the
manufacture of organic compounds. Sodium chloride NaCl, is a very important
compound found everywhere in the environment. Other applications include: in
alloys to improve their structure, in soap, in the purification of molten metals, in
sodium vapour lamps, as a heat transfer fluid and as a desiccant for drying solvents.
B.2.61 Strontium
Strontium is a bright silvery alkaline-earth metal. It commonly occurs in Nature,
averaging about 0.034% of all igneous rocks. It is found chiefly in the form of the
sulphate mineral celestine SrCO 4 and the carbonate strontianite SrCO 3 .
Principal uses of strontium compounds are in pyrotechnics, vacuum tubes to
remove the last traces of air and as the carbonate in special glass for television
screens and visual display units. Further uses of strontium and its compounds are
in toothpastes, in aerosol paint or for the medical treatment of osteoporosis.
B.2.62 Sulphur
Sulphur is a yellow solid non-metal widely distributed in Nature. The three most
important commercial sources are: 1) elemental sulphur in the caprock salt domes
in the U.S. and Mexico and the sedimentary evaporite deposits in eastern Poland
and western Asia; 2) as H 2 S in sour natural gas and as organosulphur com-
pounds in crude oil; 3) from pyrites FeS 2 and other metal-sulphide minerals.
 
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