Jeanbandyite

Chemical formula: Fe₃+Sn₄+(OH)₅O

Jeanbandyite is a rare tin and iron mineral, forming small, octahedral crystals with a characteristic dark brown to black color.

## Characteristics Jeanbandyite is a tin and iron hydroxide, belonging to the stottite group. It occurs as very small, sharply pointed octahedral crystals, rarely exceeding 1 mm in size. The crystals are usually well-formed and grown on other minerals, forming lustrous aggregates. Its color ranges from dark brown, reddish-brown to almost black, and on thin edges, it can be translucent red. ## Physical Properties This mineral is characterized by a hardness of 3.5 on the Mohs scale. It has a luster ranging from vitreous to submetallic. It is brittle, and its density is approximately 4.15 g/cm³. It is opaque, except for the thinnest fragments, which may be translucent. ## Colors and Varieties Jeanbandyite occurs in uniform colors from dark brown and reddish-brown to black. No color or commercial varieties are distinguished. ## History and Name The mineral was discovered in the Llallagua mine in Bolivia and described in 1982 by M.L. Drabble, P.J. Dunn, and Richard V. Gaines. The name honors Jean Bandy (1915-1980), an American mining engineer and mineral collector who worked in Bolivia and was the first to notice this mineral. ## Uses Due to its rarity and microscopic crystal size, jeanbandyite has no industrial application. It is solely an object of interest for collectors specializing in rare or systematic minerals.

Properties

Mohs hardness: 3.5
Luster: Vitreous to Sub-Metallic
Streak: Red-brown
Density: 4.15
Cleavage: None
Fracture: Conchoidal
Transparency: Translucent to Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Jeanbandyite can be identified by its characteristic, sharp, octahedral crystals of dark brown to black color and vitreous or submetallic luster. It usually occurs as small crystals grown on other minerals, especially in the oxidation zones of tin deposits. ## Differentiation from Similar Minerals It can be confused with other fine-grained, dark oxide minerals. Definitive differentiation from similar minerals, such as some spinels or wickmanite, requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Crystal Forms It forms exclusively small, well-formed crystals with an octahedral habit, often slightly modified. Crystals rarely exceed 1 mm and occur as single individuals or in small groups on the surface of the host rock.

Geological environment

## Genesis Jeanbandyite is a secondary mineral, forming in the oxidation zones of hydrothermal tin deposits. It forms as a result of the weathering of primary tin-bearing minerals, such as cassiterite, in the presence of iron minerals. ## Mineral Associations It most commonly co-occurs with cassiterite, quartz, pyrite, franckeite, cylindrite, and also with other secondary tin minerals, such as wickmanite. At the discovery site (Llallagua), it was found on franckeite. ## Localities The most important and classic locality is the Siglo XX mine in Llallagua, Potosí Department, Bolivia, where the mineral was discovered. Its occurrence has also been confirmed in the San José and Itos mines in Oruro, Bolivia. Outside Bolivia, it has been reported in small quantities in the Clara mine in Wolfach, in the German Black Forest.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with sharp, well-formed, lustrous crystals, clearly contrasting with a contrasting matrix (e.g., light quartz or metallic franckeite). Crystal size is a key factor - specimens with crystals approaching 1 mm are considered exceptional. The aesthetics of the overall composition and the absence of damage are also important. ## Popular Localities By far the most desirable and classic specimens come from the type locality - the Siglo XX mine in Llallagua, Bolivia. Specimens from this mine are the standard against which other finds are compared.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the brittleness and small size of the crystals, mechanical or ultrasonic cleaning is not recommended. If liquid is necessary, only distilled water should be used. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral. The crystals are brittle and sensitive to impact and scratches. Specimens should not be exposed to sudden temperature changes. ## Storage It is recommended to store jeanbandyite specimens in sealed "micromount" boxes to protect them from dust, mechanical damage, and direct contact. Display should be away from sources of vibration.

Sources

IMA Mineral List (CNMNC)