Fedotovite

Chemical formula: K<sub>2</sub>Cu<sup>2+</sup><sub>3</sub>O(S<sup>6+</sup>O<sub>4</sub>)<sub>3</sub>

Fedotovite is a rare copper and potassium sulfate, forming characteristic, dark green to black, tabular crystals in volcanic fumarole environments.

## Characteristics Fedotovite is a mineral from the sulfate group, chemically a basic copper and potassium sulfate. It occurs as small, tabular or bladed crystals, often forming radial or bladed aggregates. Its crystals are typically very dark green, brownish-green to almost black, which is typical for copper minerals forming at high temperatures. ## Physical Properties This mineral is characterized by a vitreous luster. It is translucent, and in thin fragments, even transparent. Its Mohs hardness is approximately 2.5, making it relatively soft. The density ranges from 3.23 to 3.27 g/cm³. ## Colors and Varieties Fedotovite occurs in a uniform color range, from dark green, through brownish-green, to black. No color or commercial varieties are distinguished. ## History and Name The mineral was named in honor of Sergei Aleksandrovich Fedotov (1931-2019), a Russian volcanologist and seismologist, director of the Institute of Volcanology of the Russian Academy of Sciences in Petropavlovsk-Kamchatsky. It was discovered and described in 1987 based on samples from the Tolbachik volcano in Kamchatka, Russia. ## Uses Fedotovite has no industrial application. Its significance is purely scientific and collectible, as a rare and interesting mineral associated with volcanic environments.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
Light green
Density
3.23-3.27
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Fedotovite can be identified by its characteristic dark green to black color, tabular crystal habit, and occurrence as aggregates. Its origin is key – it forms as a product of volcanic exhalations (fumaroles). ## Distinguishing from Similar Minerals It can be confused with other dark copper sulfates found in fumaroles, such as piipite or kamchatkite. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Field identification is very difficult. ## Crystal Forms Fedotovite crystals are typically tabular, flattened along the {001} plane, or bladed. They often form radial or bladed aggregates, as well as thin crusts and coatings on volcanic rocks.

Geological environment

## Genesis Fedotovite is a mineral of volcanic origin. It forms by sublimation from volcanic gases (exhalations) in high-temperature fumaroles, ranging from 400 to 600°C. It crystallizes directly on the surface of volcanic rocks, such as basalt. ## Mineral Associations This mineral co-occurs with other sulfates and oxides formed under similar conditions. It is most commonly associated with: tenorite, hematite, piipite, kamchatkite, langbeinite, aphthitalite, chalcocyanite, and dolerophanite. ## Localities The most important and type locality for fedotovite is the Tolbachik volcano on the Kamchatka Peninsula in Russia. This is the main locality from which the best-formed specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, sharp crystals of intense, dark green color. Rich aggregates of crystals on a contrasting rock matrix are also highly valued. Due to the rarity of the mineral, any well-identified specimen has collectible value. ## Popular Localities The only significant source of collectible fedotovite specimens is the Tolbachik volcanic complex in Kamchatka, Russia, particularly the fumaroles formed after the Great Fissure Eruption in 1975-1976.

Care and storage

## Cleaning Fedotovite specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its potential solubility in water, contact with liquids, especially water and acids, should be avoided. ## What to Avoid Contact with water, moisture, and chemicals must be strictly avoided. The mineral is sensitive to changes in humidity and can be damaged. It should not be heated or subjected to ultrasound. It should be protected from direct sunlight, which can cause changes in its structure. ## Storage It is recommended to store fedotovite specimens in dry conditions, preferably in tightly sealed containers or display cases with a desiccant. It should be kept away from other minerals that it might scratch or that might damage it.

Sources

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