Krennerite

Chemical formula: Au₃AgTe₈

Krennerite is a rare gold-silver telluride, forming characteristic, striated prismatic crystals with a metallic luster.

## Characteristics Krennerite is a rare mineral from the telluride group, chemically classified as a gold-silver telluride. Its crystals are typically small, prismatic in habit, often elongated and distinctly striated along the main axis. The crystal surfaces exhibit a strong, metallic luster. This mineral is brittle and opaque. It occurs as single crystals or in intergrowths with other tellurides. ## Physical Properties Krennerite is characterized by a hardness of 2.5 on the Mohs scale, making it a soft mineral. Its density is high, approximately 8.62 g/cm³. The luster is strongly metallic, and the mineral is completely opaque. It possesses perfect cleavage in one direction. ## Colors and Varieties The color of krennerite ranges from silvery-white to brass-yellow. On fresh surfaces, it is very bright, but over time it may tarnish or develop a patina. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral was first described in 1877 by the Hungarian mineralogist Joseph Krenner (1839–1920), after whom it is named. The discovery was made in the Săcărâmb mine in Romania, which is its type locality. ## Uses Due to its gold content, krennerite is a minor source of this precious metal in deposits where it occurs in larger quantities. For collectors, it is primarily a valuable and sought-after mineral due to its rarity and well-formed crystals.

Properties

Mohs hardness: 2-3
Color: Silver white
Luster: Metallic
Streak: Greenish-black
Density: 8.62
Cleavage: on {001}; Ramdohr (1969) mentions as second "very indistinct" cleavage without specifying orientation.
Fracture: Irregular/Uneven,Sub-Conchoidal
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Krennerite can be identified by its silvery-white to brass-yellow color, strong metallic luster, and characteristic, striated prismatic crystals. Its high density is also an important diagnostic feature. It is a soft and brittle mineral. ## Distinguishing from Similar Minerals Krennerite is very similar to sylvanite and calaverite, with which it often co-occurs. It differs from sylvanite by the absence of the characteristic graphic intergrowths. Distinguishing it from calaverite, which crystallizes in the monoclinic system, without laboratory analysis (e.g., XRD) is often impossible, although calaverite less frequently forms such distinctly prismatic and striated crystals. Pyrite is much harder (6-6.5) and has a different crystal form. ## Crystal Forms Krennerite crystals are columnar or prismatic, often with vertical striations on the faces. They usually occur as single, embedded crystals or in small aggregates. More rarely, it forms granular or massive aggregates.

Geological environment

## Genesis Krennerite is a hydrothermal mineral. It forms in low-temperature ore veins rich in gold and tellurium. It typically forms in the late stages of crystallization, in association with other tellurides and sulfides. ## Mineral Associations This mineral often co-occurs with other gold and silver tellurides, such as calaverite, sylvanite, petzite, and hessite. It is also accompanied by native gold, pyrite, sphalerite, tetrahedrite, quartz, dolomite, and fluorite. ## Localities The most important and historical occurrences of krennerite are in Săcărâmb (formerly Nagyág) in Romania. Other known localities include Cripple Creek in Colorado (USA), Kalgoorlie in Western Australia, and Kirkland Lake in Ontario (Canada). Occurrences have also been reported in the Fiji region (Vatukoula).

Rarity

Rare

For collectors

## Quality Criteria The most prized krennerite specimens are those with sharply terminated, well-formed, and distinctly striated crystals with a strong metallic luster. Crystal size is also very important – specimens exceeding one centimeter are exceptionally rare and sought after. The attractiveness is further enhanced by a contrasting matrix, such as white quartz, and association with other rare tellurides or native gold. ## Popular Localities Classic and most desirable specimens come from the historical locality of Săcărâmb in Romania. Very good quality crystals, often of significant size, were also provided by mines in Cripple Creek, Colorado, which are now considered the best source of this mineral.

Care and storage

## Cleaning Krennerite specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to its softness and perfect cleavage, avoid washing with water and mechanical cleaning. Ultrasonic cleaning is absolutely forbidden. ## What to Avoid Avoid contact with chemicals, acids, and detergents. The mineral is sensitive to scratches and impacts. It should not be heated or exposed to sudden temperature changes. Prolonged exposure to humid air can cause slow oxidation and tarnishing of the surface. ## Storage Krennerite should be stored in separate, padded boxes to avoid contact with harder minerals. It is best kept in stable conditions, away from sources of vibration, humidity, and direct sunlight.