Nabokoite

Chemical formula: Cu₂+₇Te₄+O₄(S₆+O₄)₅·KCl

Nabokoite is a very rare copper tellurate-sulfate, forming characteristic, small, tabular crystals of an intense green color.

## Characteristics Nabokoite is a mineral from the sulfate group, also containing tellurium, copper, potassium, and chlorine. It occurs as very small, tabular or platy crystals, rarely exceeding 1 mm. These crystals often form rosette-like or radial aggregates, as well as thin coatings and crusts on rocks. Its most characteristic feature is its intense, emerald-green to grass-green color. ## Physical Properties Nabokoite crystals exhibit a vitreous luster. The mineral is brittle and has perfect cleavage in one direction, corresponding to the flat surface of the tabular crystals. Due to the small size of the crystals, most physical properties are difficult to observe without specialized equipment. ## Colors and Varieties This mineral is known exclusively in shades of green, from emerald-green to grass-green. No varieties have been described. ## History and Name Nabokoite was discovered in the products of fumarolic activity of Tolbachik volcano in Kamchatka, Russia. It was described and recognized as a new mineral in 1987. Its name honors Sofia Ivanovna Naboko (1909-2005), a Russian geologist and volcanologist who studied Kamchatka's volcanoes, including Tolbachik, for many years. ## Uses Nabokoite has no industrial or commercial applications. Its significance is purely scientific and as a collector's item, being a very rare and interesting mineral associated with volcanic environments.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Green
Density: 4.23
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of nabokoite is based on its unique occurrence environment (volcanic fumaroles), characteristic habit of small, tabular crystals forming rosette-like aggregates, intense green color, and co-occurrence with other rare tellurium minerals. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or EDS spectroscopy. ## Distinguishing from Similar Minerals Nabokoite can be confused with other secondary, green copper minerals, such as brochantite, malachite, or other rare sulfates and tellurates. However, it is distinguished by its specific tabular crystal habit and mineral associations. It differs from brochantite in crystal form (brochantite forms acicular or prismatic crystals), and from malachite by its lack of reaction with hydrochloric acid. Final distinction from very similar minerals from the type locality (e.g., fedotovite) requires chemical analysis. ## Crystal Forms Nabokoite forms thin, tabular crystals with a square or rectangular outline. These crystals often combine into subparallel or rosette-like aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis Nabokoite is an exhalative mineral. It forms as a result of sublimation and reaction of high-temperature volcanic gases (fumaroles) (400-600°C) with surrounding rocks. It is a product of volcanic activity, crystallizing directly from the gas phase near fumarole vents. ## Mineral Associations This mineral occurs in association with other rare fumarolic minerals, such as tenorite, hematite, aphthitalite, langbeinite, and especially other copper sulfates and tellurates, e.g., atlasovite, fedotovite, kamchatite, klyuchevskite, and piipite. Co-occurrence with these minerals is a key diagnostic clue. ## Localities The only confirmed and detailed described occurrences of nabokoite in the world are fumaroles associated with the Great Fissure Eruption of Tolbachik volcano (1975-1976) on the Kamchatka Peninsula in Russia. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria The quality of nabokoite specimens is primarily assessed based on the richness and definition of the crystals. Most desirable are specimens with well-formed, sharp, tabular crystals forming aesthetic, rosette-like aggregates. The intensity and purity of the emerald-green color also increase its value. Due to the microscopic size of the crystals, their abundance on the rock matrix and contrast with the substrate are crucial. Specimens with visible, well-formed aggregates, free from damage, are highly prized. ## Popular Localities The only source of collector specimens is the type locality – Tolbachik volcano in Kamchatka. Specimens from historical collections from this locality are extremely rare and sought after by specialized collectors of systematic minerals and "micromounts."

Care and storage

## Cleaning Due to its extreme rarity, fragility, and small crystal size, mechanical cleaning is highly inadvisable. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust. Contact with water and any chemicals should be avoided. ## What to Avoid Contact with water, acids, detergents, and other liquids must be strictly avoided, as the mineral may be soluble or damaged. The crystals are very brittle and sensitive to mechanical damage, vibrations, and temperature changes. The specimen should not be exposed to direct sunlight. ## Storage Nabokoite specimens should be stored under stable conditions, in a closed, padded "micromount" box that protects them from dust, moisture, and physical damage. It is best to keep them in a dry place, away from heat and light sources.

Sources

IMA Mineral List (CNMNC)