Paratobermorite
Chemical formula: [Ca(H₂O)₃]Ca₄(Al₀.₅Si₀.₅)₂Si₄O₁₆(OH)(H₂O)₂
A rare calcium silicate of white color and silky luster, forming tiny, acicular crystals within metasomatically altered limestone rocks.
Properties
- Mohs hardness
- 3.5
- Color
- Colourless, pale yellowish, pale beige, or pinkish
- Luster
- Silky
- Streak
- White
- Density
- 2.51
- Cleavage
- on (001)
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Paratobermorite is difficult to identify visually without specialized equipment. Its characteristic forms of occurrence are radial aggregates and spherulites composed of very fine, acicular or bladed crystals. White color, silky luster, and occurrence in a specific geological environment (altered manganese rocks) are important clues. ## Distinguishing from Similar Minerals It can be confused with other white, fibrous zeolite minerals or silicates, such as tobermorite, okenite, or thomsonite. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), due to subtle differences in crystal structure and chemical composition. ## Crystal Forms Paratobermorite crystals are elongated, bladed, or acicular. They typically form radial, spherical aggregates (spherulites) or chaotic, felted clusters. Less commonly, they are observed as rosettes or coatings on other minerals.
Geological environment
## Genesis Paratobermorite is a secondary mineral, formed by low-temperature hydrothermal or metasomatic processes. It forms within manganese ore deposits that have undergone alteration, often in voids and fractures of rocks. Its formation is associated with the circulation of solutions rich in calcium and silica. ## Mineral Associations This mineral co-occurs with other rare minerals characteristic of the Kalahari manganese deposits. The most common associations include: hausmannite, calcite, hematite, barite, as well as other silicates such as tobermorite, oyelite, or marokite. ## Localities The most important and best-documented paratobermorite localities in the world are found in the Kalahari manganese field in South Africa, especially in the Wessels and N'Chwaning II mines in the Hotazel area. These are the localities from which the best specimens of this mineral originate.
Rarity
Very rare
For collectors
## Quality Criteria Paratobermorite's collector appeal depends on several factors. Specimens with well-formed, spherical aggregates (spherulites) with a distinctly radial structure are most highly valued. The size of these aggregates is important – the larger they are, the more valuable the specimen. Contrast with dark matrix rock (most often hausmannite) significantly enhances aesthetic qualities. Purity (lack of damage to delicate fibers) is crucial. ## Popular Localities By far the most prized and sought-after paratobermorite specimens by collectors come from the Wessels and N'Chwaning mines in the Kalahari Basin, South Africa. Specimens from these localities are considered the global standard for this mineral.
Care and storage
## Cleaning Paratobermorite specimens are very delicate and brittle. They should only be cleaned very carefully, using compressed air to remove dust. Any contact with water or chemicals is inadvisable and can lead to damage or disintegration of the aggregates. ## What to Avoid Contact with water, acids, and other chemical agents should be strictly avoided. The mineral's structure is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. Vibrations and impacts can easily destroy the delicate, fibrous crystals. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "membrane box" type or in boxes with soft lining) that protect them from dust, humidity, and mechanical damage. Display should occur under controlled, low humidity conditions.