|Molar mass||294.7 g/mol|
|Density||8.216 g/cm3, solid|
|Melting point||896.85 °C|
|Solubility in water||insoluble|
|Band gap||0.15 eV |
|Crystal structure||orthorhombic, oP12|
|Space group||P212121, No. 19|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the source of the selenide (Se2-) anion combining with the silver in the toning process.
It is found in nature as the mineral naumannite, a comparatively rare silver mineral which has nevertheless become recognized as important silver compound in some low-sulfer silver ores from mines in Nevada.
Silver selenide normally exists in the orthorhombic β-phase but at temperatures above 130 °C transforms into the cubic α-Ag2Se (Space group Im-3m, No. 229, Pearson symbol cI20). The phase transition increases ionic conductivity by 10,000 times to about 2 S/cm 
- O. Madelung (2004). Semiconductors: data handbook. Birkhäuser. p. 461. ISBN 3-540-40488-0.
- http://nevada-outback-gems.com/Reference_pages/sulfide_ores.htm Notes on naumannite.
- Kirchhoff F., Holender J.M., Gillan M.J. (1996). "Structure, dynamics, and electronic structure of liquid Ag-Se alloys investigated by ab initio simulation". Physical Review B 54: 190–202. doi:10.1103/PhysRevB.54.190.
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