Revdite
Chemical formula: Na₁₆Si₁₆O₂₇(OH)₂₆·28H₂O
Rewdite is a rare, colorless or white sodium silicate, forming flexible, fibrous aggregates with a silky luster.
Properties
- Mohs hardness
- 2
- Color
- Colourless, white
- Luster
- Silky
- Streak
- White
- Density
- 1.94
- Cleavage
- Perfect on {100}, less perfect on {010}
- Fracture
- Splintery
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of rewdite is its mode of occurrence - aggregates of very fine, flexible, white fibers with a silky luster, resembling cotton wool or asbestos. Its low hardness and water solubility are also characteristic. ## Distinguishing from Similar Minerals Rewdite can be confused with other fibrous minerals, such as natrolite, okenite, or some serpentines (chrysotile). It differs from natrolite by the greater elasticity of its fibers. Okenite forms similar aggregates but is insoluble in water. Chrysotile (asbestos) has more elastic and resistant fibers. Final differentiation often requires advanced studies, e.g., by XRD method. ## Crystal Forms Rewdite forms elongated, acicular or bladed crystals that combine into tangled, fibrous or felted aggregates. Individual crystals are rarely visible to the naked eye.
Geological environment
## Genesis Rewdite is a hydrothermal mineral. It forms in the late stages of crystallization in ultra-alkaline pegmatites and associated hydrothermal veins, cutting nepheline syenites and other alkaline rocks. It forms as a result of the activity of sodium- and silica-rich solutions at relatively low temperatures. ## Mineral Associations This mineral coexists with other rare alkaline minerals. In the Khibiny and Lovozero massifs (Kola Peninsula, Russia), its associations include natrite, thermonatrite, eudialyte, lorenzenite, nepheline, microcline, aegirine, as well as other rare sodium silicates like canasite or tinaksite. ## Localities The most important and best-documented occurrences of rewdite in the world are located in Russia, on the Kola Peninsula, in the alkaline massifs of Khibiny (Mount Rasvumchorr) and Lovozero (Mount Karnasurt, Alluaiv). These are its discovery sites and the main source of collector specimens.
Rarity
Very rare
For collectors
## Quality Criteria The most prized rewdite specimens are those that form rich, "fluffy" aggregates of pure, white fibers, free from impurities and mechanical damage. Contrast with a darker host rock (matrix) significantly enhances the visual appeal of the specimen. Due to the mineral's delicacy, its integrity and lack of broken fibers are crucial. ## Popular Localities The vast majority, if not all, collector specimens of rewdite come from its type locality and surrounding occurrences on the Kola Peninsula in Russia, especially from the Khibiny and Lovozero massifs. Specimens from these locations are the standard for this mineral.
Care and storage
## Cleaning Rewdite specimens are extremely delicate and fragile. Wet cleaning should be avoided, as the mineral is water-soluble. Dust can be removed very carefully with a soft brush or a stream of compressed air from a distance and at low pressure. ## What to Avoid Contact with water and other liquids that can dissolve or damage the delicate fibers must be absolutely avoided. The mineral is sensitive to acids. It should be protected from shocks, impacts, and pressure, which can destroy its structure. ## Storage Rewdite specimens are best stored in closed, padded boxes or "micromount" containers, which protect them from dust, moisture, and mechanical damage. It should not be touched with fingers to avoid transferring moisture and contaminants.