Barbosalite
Chemical formula: Fe<sup>2+</sup>Fe<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>
Barbosalite is a rare, dark blue to black phosphate mineral, forming aggregates of small crystals in granitic pegmatites.
Properties
- Mohs hardness
- 5.5-6
- Luster
- Vitreous to Sub-Metallic
- Streak
- Greenish-grey
- Density
- 3.60
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Barbosalite is identified by its characteristic very dark bluish-black or greenish-black color, relatively high hardness (5.5-6), and occurrence as massive, granular, or radial aggregates in pegmatites. A greenish-gray streak is also an important diagnostic feature. ## Distinguishing from Similar Minerals Barbosalite can be confused with other dark phosphates such as lazulite, scorzalite, or rockbridgeite. From lazulite and scorzalite, with which it forms isomorphic series, it is usually distinguished by its darker, almost black color and chemical composition (dominance of iron). Distinguishing it from rockbridgeite, which often co-occurs, can be difficult without advanced analyses (XRD), although rockbridgeite more often forms fibrous aggregates with a more greenish hue. ## Crystal Forms Barbosalite crystals are rare and usually small. They take the form of short, prismatic columns, often with a square outline. Most commonly, however, this mineral occurs as massive, fine-grained aggregates, as well as in the form of radial aggregates and crusts on other minerals.
Geological environment
## Genesis Barbosalite is a secondary mineral, formed in hydrothermal zones and as a result of alteration in complex granitic pegmatites rich in phosphates. It forms from the oxidation and transformation of primary iron and manganese phosphates, such as triphylite or lithiophilite. ## Mineral Associations This mineral often co-occurs with other phosphates. Its typical associated minerals include: triphylite, heterosite, rockbridgeite, frondelite, strengite, cyrilovite, as well as quartz, muscovite, and other pegmatite minerals. ## Localities The most important and classic locality for barbosalite is the Sapucaia mine in Minas Gerais, Brazil, where it was discovered. It is also known from other pegmatites in Brazil. In the USA, it occurs in pegmatites in South Dakota (e.g., in the Keystone area), New Hampshire (Palermo mine), and Maine. It has also been reported in Rwanda (Buranga deposit), Germany (Hagendorf), and Portugal.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, even if small, lustrous crystals, which is a great rarity for this mineral. Rich radial aggregates on a contrasting rock matrix are also highly valued. Specimen purity and lack of damage are crucial. Co-occurrence with other rare phosphates enhances its appeal. ## Popular Localities Specimens from the type locality, the Sapucaia mine in Brazil, hold particular historical value. High-quality collector material, including rare crystals, also comes from pegmatites in South Dakota and New Hampshire in the USA.
Care and storage
## Cleaning Barbosalite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, compressed air can be used. Due to possible reactivity, contact with water and any chemical agents should be avoided. ## What to Avoid Contact with acids and detergents, which can damage the mineral's surface, should be avoided. Barbosalite is sensitive to sudden temperature changes. It should not be exposed to prolonged direct sunlight, which may cause it to fade. ## Storage Specimens should be stored in stable conditions, in a dry place, away from heat sources and moisture. It is best to keep them in separate, padded boxes or display cases to prevent scratches and mechanical damage.