Serrabrancaite
Chemical formula: Mn<sup>3+</sup>PO<sub>4</sub>·H<sub>2</sub>O
Serrabrancaite is a rare, hydrated manganese phosphate, forming characteristic black, fibrous aggregates with a metallic luster.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Black
- Density
- 3.11
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features of serrabrancaite are its occurrence as black, radial or felt-like aggregates, strong metallic luster, and genesis associated with pegmatites. Its black streak is also characteristic. ## Distinguishing from Similar Minerals Serrabrancaite can be confused with other black, fibrous manganese minerals, such as some oxides (e.g., hollandite, pyrolusite). Differentiation often requires advanced research methods, such as X-ray diffraction (XRD). In field conditions, distinguishing it from similar minerals may be impossible. It differs from pyrolusite by a slightly harder streak and the absence of soiling fingers. ## Crystal Forms This mineral exclusively forms very fine, acicular or hair-like crystals (acicular habit), which combine into radial, spherulitic, or tangled, felt-like aggregates.
Geological environment
## Genesis Serrabrancaite is a secondary mineral, forming in the weathering zones of granite pegmatites rich in phosphates. It forms as a result of hydrothermal alteration or oxidation of earlier manganese and phosphorus minerals under low-temperature conditions. ## Mineral Associations This mineral co-occurs with other phosphates, such as strengite, hureaulite, trolleite, rockbridgeite, as well as with quartz, muscovite, and manganese oxides. ## Localities The most important and type locality is the Serra Branca pegmatite, Pedra Lavrada, in the state of Paraíba, Brazil. This is the only confirmed and well-documented locality for this mineral worldwide.
Rarity
Very rare
For collectors
## Quality Criteria The most desirable serrabrancaite specimens are those that exhibit well-formed, radial aggregates with an intense metallic luster, set on a contrasting matrix (e.g., white quartz). The size and completeness of these delicate "suns" or "hedgehogs" are key evaluation criteria. The purity of the specimen and the absence of mechanical damage significantly increase its value. ## Popular Localities The only source of collector specimens is the discovery site – the Serra Branca pegmatite in Brazil. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Due to the fibrous and delicate nature of the aggregates, mechanical cleaning is not recommended. Only careful dust removal with a soft brush or a stream of compressed air from a safe distance is permissible. Do not use water or any cleaning fluids. ## What to Avoid Avoid contact with water, acids, and other chemicals that may react with phosphates. The aggregates are very brittle and sensitive to shocks and touch – they can easily disintegrate. Do not expose the specimen to ultrasound. ## Storage Serrabrancaite specimens require storage under stable conditions, in closed boxes or display cases, to protect them from dust and mechanical damage. It is best to store them away from vibrations and in a place where they will not be exposed to accidental touching.