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2. Mineral Occurrences
The average levels deduced from analyses carried out on samples of igneous rock taken from the surface are 0.8 ppm for Se and 0.01 ppm for Te. For the earth's crust as a whole, the "clarke" would be 0.01 ppm for selenium and 0.001 ppm for tellurium.
2.1 Selenium
Crystallized selenium is rarely found in nature, and is only reported in deposits in special cases, such as when the redox front in uranium deposits has shifted. On the other hand, selenides can be found :
copper (berzelianite, Cu 2 Se; krutaite, CuSe 2 );
lead (clausthalite, PbSe);
silver (naumannite,...
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Mineral Occurrences
Mining reserves
Bibliography
References
The world's leading producers of refined selenium and/or tellurium
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Germany
Norddeutsche Affinerie AG http://www.na-ag.com
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Belgium
Umicore (ex-Union Minière) http://www.umicore.com
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