Key information
Atomic number: 
34
Atomic weight: 
78.96
Density: 
4790 kg/m³
Boiling point: 
958.16° K
Melting point: 
490.16° K
Heat vapour: 
13.99 kJ/mol
Heat fusion: 
5.23 kJ/mol

Elemental selenium exists in several allotropic forms. An amorphous red selenium precipitates when solutions of selenious acid (H2SeO3) are reduced. The precipitate heated below its melting point changes to red selenium. The stable grey form crystallises from molten selenium.

Most of the selenium required by industry is produced as a byproduct of copper mining. It also found in the residues from the manufacture of sulphuric acid.

Electron Shell: 
Amazon Books
Image of The Last Sorcerers: The Path from Alchemy to the Periodic Table
Author: National Academy of Sciences, Richard Morris
Publisher: Henry (Joseph) Press (2003)
Binding: Hardcover, 294 pages