Naumannite

Silver(I) selenide

Names
Other names Naumannite
Identifiers
CAS Number	1302-09-6 Y
ECHA InfoCard	100.013.727
PubChem CID	6914520
Properties
Chemical formula	Ag2Se
Molar mass	294.7 g/mol
Density	8.216 g/cm3, solid
Melting point	896.85 °C (1,646.33 °F; 1,170.00 K)
Solubility in water	insoluble
Band gap	0.15 eV
Structure
Crystal structure	orthorhombic, oP12
Space group	P212121, No. 19
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

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-sulfur 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