Naumannite
A variety of Minerals
What is Naumannite?
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 (Se) 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 and Idaho.
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Naumannite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Naumannite Localities Map
See where Naumannite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Key Characteristics
Composition of Naumannite
Silver selenide has two crystal phases. At lower temperatures, it has an orthorhombic structure, β-Ag2Se. This orthorhombic phase, stable at room temperature, is a narrow-gap semiconductor, with space group P212121. The exact size of the band gap has been given variously from 0.02 eV to 0.22 eV. There is also a high temperature cubic phase, α-Ag2Se., which it transforms into at temperatures above 130 °C. This high temperature phase has space group Im3m, No. 229, Pearson symbol cI20. The phase transition increases ionic conductivity by 10,000 times to about 2 S/cm.
Quick Facts
Physical Properties
- Color
- grey-black
- Hardness (Mohs)
- 2.5
- Density
- 8.24 g/cm³
- Streak
- black
Chemical Properties
- Chemical Formula
- Ag2Se
- Elements
- Ag, Se
Also Known As
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Naumannite FAQs
How do I identify Naumannite?
Naumannite can be identified by its hardness of 2.5 on the Mohs scale, grey-black color. Look for these key characteristics when examining specimens.
What color is Naumannite?
Naumannite typically appears in grey-black. Color can vary depending on impurities and formation conditions.
How hard is Naumannite?
Naumannite has a hardness of 2.5 on the Mohs scale. This makes it a soft mineral that can be scratched easily.
What is the composition of naumannite of Naumannite?
Silver selenide has two crystal phases. At lower temperatures, it has an orthorhombic structure, β-Ag2Se. This orthorhombic phase, stable at room temperature, is a narrow-gap semiconductor, with space group P212121. The exact size of the band gap has been given variously from 0.02 eV to 0.22 eV. There is also a high temperature cubic phase, α-Ag2Se., which it transforms into at temperatures above 130 °C. This high temperature phase has space group Im3m, No. 229, Pearson symbol cI20. The phase transition increases ionic conductivity by 10,000 times to about 2 S/cm.
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