Braithwaiteite

Chemical formula: NaCu₂+₅(Ti₄+Sb₅+)O₂(As₅+O₄)₄[As₅+O₃(OH)]₂·₈H₂O

Braithwaiteite is a very rare, hydrated sodium, copper, titanium, and antimony arsenate, forming characteristic blue-green, platy crystals.

## Characteristics Braithwaiteite is a complex, hydrated arsenate from the tsumcorite group, distinguished by its unique chemical composition containing sodium, copper, titanium, and antimony. It forms elongated, platy or acicular crystals, which often occur as radial or tangled aggregates. Its intense, blue-green color makes it a distinctive and easily noticeable mineral within the paragenesis in which it occurs. ## Physical Properties Braithwaiteite crystals exhibit a vitreous luster. The mineral is translucent. Its Mohs hardness is 3, and its density is slightly greater than 4 g/cm³. It is a brittle mineral with perfect cleavage in one direction. ## Colors and Varieties Braithwaiteite occurs in a uniform, characteristic blue-green color. No color varieties or commercial varieties are known. ## History and Name The mineral was described in 2004 by Werner Krause and collaborators. Its name honors Richard S. W. Braithwaite (born 1935), a British chemist and mineralogist from the University of Manchester, in recognition of his contributions to research on secondary minerals, including arsenates. ## Uses Due to its extreme rarity, braithwaiteite has no industrial application. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Light blue
Density: 4.04
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of braithwaiteite include its intense blue-green color, platy or acicular crystal habit, radial aggregates, and occurrence in the oxidation zones of polymetallic deposits. Vitreous luster and perfect cleavage are also helpful in identification. ## Distinguishing from Similar Minerals Braithwaiteite can be confused with other secondary copper minerals of similar color, such as agardite, geminite, or some varieties of aurichalcite. Differentiation often requires advanced analytical methods (e.g., EDS/XRD), but the characteristic platy habit and paragenesis with titanium and antimony minerals can be an indication. ## Crystal Forms This mineral forms elongated, flattened, platy crystals, often with pointed terminations. These crystals combine into radial, star-shaped, or haphazardly tangled aggregates, as well as fibrous masses.

Geological environment

## Genesis Braithwaiteite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic ore deposits. It crystallizes in vugs and fissures in rocks, most often quartzites, as a result of the weathering of primary minerals containing copper, arsenic, antimony, and titanium. ## Mineral Associations This mineral co-occurs with other rare secondary minerals. In its type locality (Tsumeb mine), it was found in association with quartz, tennantite, chalcocite, gallite, germanite, renierite, cinnabar, hematite, as well as rare arsenates such as ludlockite, schneiderhöhnite, stottite, and leiteite. ## Localities The only confirmed and described occurrence of braithwaiteite in the world is the historic Tsumeb mine in Namibia, which is its type locality. This is one of the most famous mineralogical sites in the world, known for its extraordinary diversity and quality of specimens, including many unique secondary minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valued braithwaiteite specimens are those that exhibit well-formed, sharply terminated crystals of intense, blue-green color, forming aesthetic, radial aggregates. Contrast with a light matrix rock (quartz) significantly enhances visual appeal. Due to the microscopic size of the crystals, their quality and form visible under magnification are crucial. ## Popular Localities The only source of braithwaiteite specimens is the Tsumeb mine in Namibia. All specimens available on the collector's market come from this single, historic locality.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to the presence of arsenic, inhalation of dust should be avoided. Washing hands after contact with the mineral is recommended. The use of water is inadvisable due to the risk of damaging delicate crystals and potential reactions. ## What to Avoid Avoid contact with all chemicals, especially acids, which can destroy the mineral. Protect it from high temperatures, which can lead to dehydration and structural changes. It is a brittle mineral, so avoid ultrasound, vibrations, and impacts. ## Storage Braithwaiteite specimens are best stored in sealed, stable containers (e.g., "micromount boxes") to protect them from dust, mechanical damage, and sudden changes in humidity. Store away from heat sources and direct sunlight.

Sources

IMA Mineral List (CNMNC)