Ferri-pedrizite
Chemical formula: NaLi<sub>2</sub>[Fe<sup>3+</sup><sub>2</sub>Mg<sub>2</sub>Li]Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>
Ferri-pedrizite is an extremely rare mineral from the amphibole group, characterized by a dark green to black color and a complex chemical composition.
Properties
- Mohs hardness
- 6
- Luster
- Vitreous
- Streak
- Light gray
- Density
- 3.21
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying ferri-pedrizite in the field is practically impossible and requires advanced analytical techniques, such as spectroscopy and chemical analysis (EDS/WDS). In a collection, it can be tentatively identified based on its dark color, prismatic habit, and co-occurrence with other rare lithium minerals. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as arfvedsonite, riebeckite, or ferro-actinolite. Definitive differentiation is possible only through detailed chemical analysis, especially the lithium content and the Fe²⁺ to Fe³⁺ ratio. ## Crystal Forms Ferri-pedrizite forms columnar or acicular crystals, often gathered in radial or fibrous aggregates. Well-formed, single crystals are exceptionally rare.
Geological environment
## Genesis This is a magmatic mineral, crystallizing in the late stages in granitic pegmatites, especially in zones rich in lithium and sodium. It forms under conditions of low pressure and relatively low temperatures compared to other magmatic processes. ## Mineral Associations It most commonly co-occurs with albite, quartz, microcline, and also with other lithium minerals such as lepidolite or elbaite (lithium tourmaline). ## Localities The only confirmed and thoroughly described locality for this mineral in the world is the Água Boa pegmatite in the municipality of Capelinha, Minas Gerais state, Brazil. This is the type locality for this mineral.
Rarity
Extremely rare
For collectors
## Quality Criteria The most desirable specimens are those that contain clearly formed, even if small, prismatic crystals with an intense, dark green color. A well-defined association with other pegmatitic minerals is also crucial, as it enhances the aesthetic and scientific value of the specimen. Due to its rarity, every authentic specimen is valuable. ## Popular Localities The only source of ferri-pedrizite specimens is its type locality in Minas Gerais, Brazil. Material from this location is extremely difficult to acquire on the collector's market.
Care and storage
## Cleaning It is recommended to clean only with a soft brush to remove dust. Avoid contact with water and any chemical agents that could react with the mineral. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, and sudden temperature changes. The mineral should be protected from prolonged exposure to direct sunlight. ## Storage Ferri-pedrizite specimens, due to their rarity and potential fragility, are best stored in individual, padded collector boxes (e.g., "perky boxes") to prevent mechanical damage and abrasion. Store in stable humidity conditions.