Tungusite

Chemical formula: Ca₁₄Fe²⁺₉Si₂₄O₆₀(OH)₂₂

Tungusite is a very rare, hydrated calcium and iron silicate, forming fine, fibrous aggregates of a greenish color.

## Characteristics Tungusite is a mineral from the silicate group, characterized by a complex chemical composition. It occurs extremely rarely, forming fibrous or lamellar aggregates that can take on forms resembling asbestos. Individual "fibers" or lamellae are flexible. It is usually found as thin veins or pockets within volcanic rocks. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 2. It is opaque, with a luster described as silky or dull, which is typical for its fibrous structure. The density of tungusite is similar to that of other silicates, around 2.76 g/cm³. ## Colors and Varieties Tungusite most often ranges in color from greenish to grayish-green. No distinct color or commercial varieties have been identified. ## History and Name The mineral's name comes from its discovery location and first description – the region of the Nizhnyaya Tunguska River in Siberia, Russia. It was first described in 1966 by V.I. Kudryashova. ## Applications Due to its extreme rarity, tungusite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness: 2
Color: Yellow-green, grass-green
Luster: Silky
Streak: White
Density: 2.59
Cleavage: Perfect on {001}
Fracture: Splintery
Transparency: Transparent
Crystal system: Triclinic

Diagnostic features

## Identification Characteristic features of tungusite include its fibrous or lamellar structure, silky luster, and greenish color. It occurs in the form of flexible aggregates. However, identification most often requires advanced research methods due to its similarity to other silicates. ## Distinguishing from Similar Minerals Tungusite can be confused with minerals from the serpentine group (e.g., chrysotile) or other fibrous silicates. Distinguishing it based on visual characteristics is very difficult and usually requires chemical analysis (EDS) or X-ray diffraction (XRD) to confirm its unique structure and composition. ## Crystal Forms This mineral does not form well-developed, single crystals. It occurs as fibrous, lamellar, or scaly aggregates, often forming felted aggregates resembling asbestos.

Geological environment

## Genesis Tungusite is a low-temperature hydrothermal mineral. It forms in voids and fissures within volcanic rocks, such as basalts and diabases, often in their alteration zones. ## Mineral Associations It most commonly co-occurs with calcite, zeolites (such as laumontite and analcime), prehnite, quartz, and minerals from the chlorite group. At its type locality, it was also found in association with apophyllite and tobermorite. ## Localities The most important and classic tungusite localities are in Russia, Siberia, in the region of the Nizhnyaya Tunguska and Angara rivers. These are the only confirmed locations from which well-studied specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the abundance and quality of tungusite aggregates on the rock matrix are most important. Specimens with clearly visible, dense fibrous aggregates of an intense, greenish color are highly valued. Association with other well-formed minerals, such as zeolites or calcite, is also important. ## Popular Localities The only source of collector specimens is Siberia in Russia, specifically localities along the Nizhnyaya Tunguska River. Specimens from this region are considered type material and are the most sought after.

Care and storage

## Cleaning Tungusite specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its fibrous and potentially fragile nature, avoid washing it in water, especially in ultrasonic cleaners. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The mineral is soft and susceptible to mechanical damage. Protect it from high temperatures and sudden temperature changes. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust, light, and physical damage. Due to its fibrous structure, avoid touching with bare hands to prevent damage to the delicate aggregates.

External references

https://www.mindat.org/min-4055.html