Krennerite is a gold–silver telluride mineral belonging to the telluride group. Its idealized chemical formula is (Au,Ag)Te₂, indicating that gold is the dominant metal but silver frequently substitutes for a portion of the gold in the crystal lattice. The mineral is closely related to calaverite, another AuTe₂ telluride, and is distinguished primarily by its crystallographic symmetry.
Chemical composition
- Formula: (Au,Ag)Te₂
- Molar mass: Approximately 497 g mol⁻¹ (varying with the Ag/Au ratio)
- Elemental constituents: Gold (Au), silver (Ag), tellurium (Te)
Crystallography
- Crystal system: Orthorh‑omic (the orthorhombic polymorph of AuTe₂)
- Space group: Pma2 (or a closely related orthorhombic group, as reported in mineralogical literature)
- Unit‑cell parameters: a ≈ 12.08 Å, b ≈ 5.58 Å, c ≈ 9.88 Å (values dependent on compositional variations)
The orthorhombic symmetry distinguishes krennerite from the monoclinic calaverite, although both share the same chemical composition.
Physical properties
- Color: Silver‑white to pale golden‑yellow; may appear tarnished with exposure to air
- Crystal habit: Typically occurs as massive aggregates; rarely forms well‑developed orthorhombic prisms or tabular crystals
- Hardness: 2.5–3 on the Mohs scale
- Specific gravity: 8.2–8.5, reflecting its high gold and silver content
- Luster: Metallic, with a bright, reflective surface when freshly broken
- Streak: Greenish‑gray to black
Occurrence and associated minerals
Krennerite is most commonly found in hydrothermal gold‑bearing veins, particularly in environments where tellurium is present. It frequently occurs together with other telluride minerals such as calaverite, native gold, sylvanite, and petzite, as well as sulfide minerals like pyrite and arsenopyrite. Notable localities include:
- Spain: Historic telluride deposits of the Iberian Peninsula.
- United States: Vein deposits in Nevada (e.g., the Carissa and Goldfield districts).
- Other occurrences: Reported from ore bodies in Australia, Canada, and the Democratic Republic of the Congo.
History and nomenclature
The mineral was first described in the mid‑19th century from specimens collected in European telluride districts. It was named in honor of the Austrian mineralogist Krenner, who made significant contributions to the study of telluride minerals. The exact given name of the honoree varies among historical sources, but the eponym reflects his recognized authority in mineralogy at the time of the mineral’s identification.
Uses
Because krennerite contains gold, it is of economic interest in gold‑bearing ore processing. However, its relatively rare occurrence and the difficulty of separating tellurides from associated sulfides often limit direct exploitation. In mineral collections, well‑preserved specimens are valued for their distinctive metallic appearance and as representatives of telluride mineralogy.
See also
- Calaverite – the monoclinic polymorph of AuTe₂.
- Sylvanite – a silver‑gold telluride with formula AgAuTe₄.
- Telluride mineral group – a class of minerals containing tellurium combined with metals.
References
- Mindat.org. “Krennerite.” Accessed 2026.
- Palache, C., H. Berman, and C. Frondel. Dana’s System of Mineralogy, 7th ed., Wiley, 2002.
- Deer, W. A., et al. An Introduction to the Rock-Forming Minerals, 2nd ed., Longman, 1997.
This entry presents information compiled from established mineralogical references and databases. No speculative statements are included.
