Taneyamalite

Chemical formula: (Na,Ca)Mn₂+₁₂(Si,Al)₁₂(O,OH)₄₄

Taneyamalite is a rare mineral from the pyroxenoid group, forming dark brown to black, platy or fibrous aggregates.

## Characteristics Taneyamalite is a complex sodium, calcium, and manganese silicate, belonging to the pyroxenoid group. It occurs as platy, bladed, or fibrous crystals, often forming radial aggregates. Its color is typically dark brown to black, giving it an inconspicuous appearance. ## Physical Properties This mineral is opaque and characterized by a vitreous luster. It is relatively brittle. Its Mohs hardness is approximately 5.5-6, and its density ranges between 3.45 and 3.55 g/cm³. ## History and Name The name taneyamalite comes from its discovery locality – the Taneyama mine in Kagoshima Prefecture, Japan. The mineral was first described in 1991 by Japanese mineralogists who identified it in manganese deposits.

Properties

Mohs hardness: 5.5 - 6
Luster: Vitreous
Streak: Brown
Density: 3.45 - 3.55
Cleavage: Perfect on {100}, Good on {010}
Fracture: Uneven
Transparency: Opaque
Crystal system: Triclinic

Diagnostic features

## Identification Taneyamalite is identified by its dark, brownish-black color, mode of occurrence (fibrous or bladed aggregates), and association with other manganese minerals. Its vitreous luster on fresh surfaces is also characteristic. ## Distinguishing from Similar Minerals It can be confused with other dark manganese minerals, such as pyrolusite or hausmannite. Differentiation often requires advanced research methods, such as chemical analysis (EDS) or X-ray diffraction (XRD), due to similarities in physical properties. ## Crystal Forms Taneyamalite crystals are usually very small, with a platy or bladed habit. Most often, they form fibrous, radial, or felted aggregates in rock fissures.

Geological environment

## Genesis Taneyamalite forms as a result of metamorphic processes in manganese ore deposits. It forms in veins cutting through these deposits, often in the presence of other manganese silicates. ## Mineral Associations This mineral co-occurs with other manganese minerals, such as rhodochrosite, tephroite, sonolite, galaxite, as well as quartz and calcite. ## Localities The most important and type locality for taneyamalite is the Taneyama mine in Kagoshima Prefecture, Japan. It has also been identified in several other locations worldwide, including the N’Chwaning mine in South Africa and in Sweden.

Rarity

Very rare

For collectors

## Quality Criteria The collector quality of taneyamalite primarily depends on the richness and development of the crystals. Specimens with clearly visible, radial aggregates on a contrasting matrix are most valued. Due to its rarity, even microscopic but well-identified crystals are valuable to collectors specializing in rare or systematic minerals. ## Popular Localities Undoubtedly, the most sought-after specimens come from the type locality – the Taneyama mine in Japan. Material from other localities, such as South Africa, is also valuable from a scientific and collecting perspective.

Care and storage

## Cleaning It is recommended to clean taneyamalite specimens only with a soft, dry brush to remove dust. Avoid water and chemical agents, which could react with the mineral or its surroundings. ## What to Avoid Avoid contact with acids and other chemicals. Due to its brittleness, protect it from impacts and sudden temperature changes. ## Storage Taneyamalite specimens should be stored in stable conditions, in a dry place, away from direct sunlight. It is best to place them in a closed display box to limit dust accumulation and the risk of mechanical damage.

Sources

IMA Mineral List (CNMNC)