Klyuchevskite
Chemical formula: K₃Cu²⁺₃Fe³⁺O₂(S⁶⁺O₄)₄
Klyuchevskite is a rare potassium, copper, and iron sulfate, forming black, tabular crystals with a metallic luster.
Properties
- Mohs hardness
- 3.5
- Color
- Dark green to olive-green
- Luster
- Vitreous
- Streak
- Pale green
- Density
- 3.00
- Cleavage
- On {h0l}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Klyuchevskite is recognizable by its black color, metallic luster, and characteristic form of small, tabular crystals. Its specific occurrence environment – volcanic fumaroles – is key for identification. ## Distinguishing from Similar Minerals It can be confused with other black, microcrystalline minerals found in fumaroles, such as tenorite (CuO) or hematite (Fe₂O₃). It differs from tenorite in crystal habit (tenorite often forms earthy or acicular aggregates), and from hematite in luster and form. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline, as well as platy crystals. They usually occur as irregular aggregates, rosettes, or coatings on volcanic rocks.
Geological environment
## Genesis Klyuchevskite is a mineral of volcanic origin. It forms through sublimation from volcanic gases (exhalations) in high-temperature fumaroles (500-600°C). It crystallizes directly from the gas phase on the surface of lava or volcanic ash. ## Mineral Associations It co-occurs with other minerals formed under similar conditions, such as tenorite, hematite, aphthitalite, langbeinite, anglesite, chalcocyanite, as well as newly discovered copper and potassium sulfates. ## Localities The only confirmed occurrence of klyuchevskite in the world is its type locality – the fumaroles of the second cone formed during the great fissure eruption of Tolbachik volcano in 1975-1976, and the fumaroles of Klyuchevskaya Sopka volcano, both on Kamchatka, Russia.
Rarity
Very rare
For collectors
## Quality Criteria The quality of a klyuchevskite specimen is primarily judged by the abundance and development of its crystals. The most valued specimens are those with clearly visible, well-formed, lustrous tabular crystals, forming rich aggregates on a small fragment of the matrix rock. Contrast with a lighter substrate also enhances visual appeal. ## Popular Localities The only source of klyuchevskite specimens is the Tolbachik volcanic complex and Klyuchevskaya Sopka volcano on Kamchatka, Russia. Specimens from these localities are extremely rare and sought after by collectors specializing in minerals from specific localities (so-called "locality collectors") and systematic mineral collectors.
Care and storage
## Cleaning Due to the small size and fragility of the crystals, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid The mineral is a product of volcanic exhalations and may be unstable under conditions different from those in which it formed. Absolutely avoid contact with water, acids, cleaning agents, and high humidity. It should not be heated or exposed to temperature changes. ## Storage Klyuchevskite specimens should be stored under stable conditions, preferably in a sealed, airtight "micromount" box, away from moisture, dust, and direct sunlight. Storage in a room with controlled, low humidity is recommended.