Berndtite-4H

Chemical formula: SnS<sub>₂</sub>

Berndtite-4H is a rare tin sulfide, forming small, hexagonal plates with a metallic luster and yellowish-brown color.

## Characteristics Berndtite-4H is a tin sulfide and one of the polytypes of berndtite. It occurs as very small, hexagonal, tabular or platy crystals, rarely exceeding 1 mm. It also forms rosette aggregates and coatings. Its characteristic features include a yellowish-brown to brown color and a metallic luster. ## Physical Properties Berndtite-4H crystals are very soft, with a Mohs hardness of only 1, meaning they can be scratched with a fingernail. They are flexible but inelastic. This mineral exhibits perfect cleavage in one direction, which is typical for its layered structure. It has a relatively high density, approximately 4.96 g/cm³. ## Colors and Varieties Berndtite-4H occurs in shades from yellowish-brown and brown to brownish-gray. No color or commercial varieties are distinguished. ## History and Name The name "berndtite" honors Dr. Fritz Berndt (1899–1945), a German mineralogist and expert on ore deposits. The suffix "-4H" refers to its hexagonal symmetry (H) and four-layered unit cell (4), distinguishing it from other polytypes, such as berndtite-2T. The mineral was first described in 1963 based on material from the Uncía mine in Bolivia. ## Uses Berndtite-4H has no industrial applications. It is of purely scientific and collector's interest as a rare tin mineral.

Properties

Mohs hardness: 1
Luster: Metallic
Streak: Pale brownish-yellow
Density: 4.96
Cleavage: Perfect on {0001}
Fracture: Micaceous
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Berndtite-4H is recognized by its characteristic appearance: small, hexagonal, yellowish-brown plates with a metallic luster. Key features include extreme softness (Mohs hardness 1) and perfect cleavage in one direction. It occurs as very fine crystals, often requiring magnification for identification. ## Distinguishing from Similar Minerals It can be confused with other minerals of similar appearance, such as molybdenite, which is, however, silvery-gray, not brown. Other tin sulfides, like teallite, have a different, lead-gray color and different crystal forms. It can only be distinguished from other berndtite polytypes using advanced analytical methods, such as X-ray diffraction. ## Crystal Forms Crystals are usually very small, thin, and tabular, with a distinctly hexagonal outline. They often form rosette or radial aggregates, as well as thin coatings and crusts on other minerals.

Geological environment

## Genesis Berndtite-4H is a hydrothermal mineral. It forms in low-temperature ore veins, usually in paragenesis with other tin and lead sulfides. ## Mineral Associations It most commonly co-occurs with cassiterite, pyrite, sphalerite, franckeite, cylindrite, and teallite. It occurs directly on these minerals or in their close vicinity. ## Localities The most important and classic locality (type locality) is the Siglo XX mine in Uncía, Potosí Department, Bolivia. This is the main locality from which the best-formed specimens of this mineral originate. Other confirmed occurrences are very few.

Rarity

Very rare

For collectors

## Quality Criteria The most prized berndtite-4H specimens are those with well-formed, sharp, hexagonal crystals forming aesthetic, rosette aggregates. Contrast with the host rock (matrix) on which they occur is important. Due to the small size of the crystals, specimens are usually "micromount" type, and their value increases with the size and perfection of the crystals. ## Popular Localities The only source of collector-quality specimens is the historical locality in Uncía, Bolivia. Specimens from this location are considered classic and most sought after by collectors specializing in rare minerals or systematics.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to its extreme softness and perfect cleavage, contact with water, brushes, or cloths should be avoided, as these can permanently damage the delicate crystals. ## What to Avoid All chemicals, including acids and detergents, should be avoided. The mineral is very soft and easily scratched or delaminated. It should be protected from vibrations, impacts, and high temperatures. ## Storage Berndtite-4H specimens should be stored in stable, sealed "micromount" containers, lined with soft material to prevent any mechanical damage. They should be kept away from other minerals to avoid scratches.

Sources

IMA Mineral List (CNMNC)