Carlosbarbosaite

Chemical formula: (U₆+O₂)₂Nb₅+₂O₆(OH)₂·₂H₂O

Carlosbarbosait is an extremely rare niobium and uranium mineral, forming acicular crystals of intense yellow color and silky luster.

## Characteristics Carlosbarbosait is a secondary mineral of the niobate group, chemically a hydrated uranyl niobo-hydroxide. It occurs as small, radial or tangled aggregates, composed of very fine, acicular or fibrous crystals. Its most characteristic feature is its intense, lemon-yellow to yellowish-brown color. Due to the presence of uranium, this mineral is radioactive. ## Physical Properties Crystals exhibit a silky luster, transitioning to adamantine on terminal faces. The mineral is translucent. Hardness has not been precisely determined due to the small size and fragility of the crystals. The density calculated based on chemical composition and unit cell parameters is 5.78 g/cm³. ## Colors and Varieties This mineral occurs in uniform shades, from light yellow and lemon-yellow to a darker, yellowish-brown. No varieties have been distinguished. ## History and Name Carlosbarbosait was first described in 2012. Its name honors Carlos do Prado Barbosa (1917–2003), a Brazilian mining engineer and mineralogist who made significant contributions to the study of Brazilian pegmatites. The type locality (locus typicus) is the Jaguaraçu pegmatite in the municipality of Coronel Murta, Minas Gerais state, Brazil. ## Applications As an extremely rare mineral, carlosbarbosait has no industrial applications. It is solely of scientific interest and is an object of interest for advanced collectors of rare minerals.

Properties

Luster: Silky to Adamantine
Streak: Light yellow
Density: 5.78
Cleavage: Perfect on {010}, Good on {100}
Transparency: Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Key features for identifying carlosbarbosait are: intense yellow color, acicular or fibrous habit of crystals forming radial aggregates, silky luster, and strong radioactivity. Occurrence in the oxidation zone of granite pegmatites rich in niobium is also an important clue. ## Distinguishing from Similar Minerals Carlosbarbosait can be confused with other secondary uranium minerals of yellow color, such as carnotite, meta-autunite, or uranophane. Visual distinction is very difficult and often impossible without advanced analysis. It is crucial to confirm the presence of niobium in the chemical composition (e.g., by EDS analysis), which distinguishes it from most common uranyl minerals. ## Crystal Forms It forms elongated, acicular or fibrous crystals with a bladed cross-section. These crystals usually occur as radial or tangled aggregates and spherulites, rarely as single needles.

Geological environment

## Genesis Carlosbarbosait is a secondary mineral, formed in the oxidation zones of complex granite pegmatites. It forms as a result of hydrothermal alteration or weathering of primary uranium and niobium-bearing minerals, such as columbite or betafite. ## Mineral Associations It co-occurs with minerals such as albite, muscovite, quartz, columbite-(Fe), and betafite. ## Localities This is an extremely rare mineral, known almost exclusively from its type locality – the Jaguaraçu pegmatite, located in Coronel Murta, in the Jequitinhonha Valley, Minas Gerais state, Brazil.

Rarity

Extremely rare

For collectors

## Quality Criteria Carlosbarbosait specimens are almost exclusively micromounts. Their value is primarily determined by the richness and aesthetics of the aggregates – the denser and better-formed radial clusters, the more valuable the specimen. The intensity of the color and the absence of damage to the delicate needles are also important. A contrasting matrix, e.g., white albite, enhances visual appeal. ## Popular Localities The only source of collector specimens is the type locality in Minas Gerais, Brazil. Material from this location is very limited and rarely appears on the market.

Care and storage

## Cleaning Carlosbarbosait specimens are extremely delicate and fragile. Cleaning should be kept to an absolute minimum. A soft brush or a photographic blower bulb can be used to remove dust. Avoid any contact with water and chemical agents. ## What to Avoid The mineral is highly radioactive. It is absolutely essential to avoid inhaling dust and direct, prolonged skin contact. Wash hands after every contact with the specimen. Do not store in areas of permanent human presence (desks, bedrooms). Protect from moisture, chemicals, and mechanical damage. ## Storage It is recommended to store specimens in sealed, lead-lined or glass containers, clearly marked as radioactive material. The best place is a dedicated display case or box, away from other minerals that could be damaged by radiation.

Sources

IMA Mineral List (CNMNC)