Quijarroite

Chemical formula: Cu₁+₆Hg₂+Pb₂+₂Bi₃+₄Se₂-₁₂

Quijarroite is a rare, lead-gray selenide of copper, lead, mercury, and bismuth, forming microscopic, spindle-shaped crystals.

## Characteristics Quijarroite is a very rare mineral belonging to the sulfosalt group, specifically a selenosalt. Its complex chemical composition includes copper, mercury, lead, bismuth, and selenium. It forms very small, spindle-shaped or platy crystals, rarely exceeding 100 micrometers in length. It typically occurs as inclusions within other minerals, mainly umangite. Observed under a reflected light microscope, it appears cream-white to gray, with a slight reddish tint. ## Physical Properties Due to the microscopic size of its crystals, most physical properties have not been precisely determined. Hardness is estimated based on similar minerals and is approximately 2.5-3 on the Mohs scale. It has a metallic luster and is opaque. The density calculated from its chemical formula and unit cell parameters is 7.64 g/cm³. ## History and Name The mineral was discovered in the El Dragón mine in the Potosí Department, Bolivia. It was officially recognized by the International Mineralogical Association (IMA) in 2016 (IMA2016-013). The name honors Telésforo Quijarro, a 19th-century Bolivian mine owner and mineral collector whose collection formed the basis of the Natural History Museum in Paris.

Properties

Mohs hardness: 2.5-3
Luster: Metallic
Streak: Black
Density: 7.64
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of quijarroite is only possible using advanced laboratory methods, such as electron microprobe analysis (EDS/WDS) for chemical composition and X-ray diffraction (XRD). Visually, under a reflected light microscope, its cream-white color and characteristic pleochroism from gray to reddish-gray can be observed. ## Differentiation from Similar Minerals Under the microscope, it can be confused with other bismuth selenides and sulfosalts, such as klockmannite, umangite, clausthalite, or watkinsite. Definitive differentiation requires chemical analysis, which will show the simultaneous presence of copper, lead, mercury, and bismuth in characteristic proportions. ## Crystal Forms Quijarroite forms elongated, spindle-shaped or platy crystals with a rhombic cross-section. It occurs as single, isolated crystals or small, randomly oriented aggregates, most often as inclusions in umangite.

Geological environment

## Genesis Quijarroite forms under hydrothermal conditions, in selenium-rich veins. In its type locality (El Dragón mine), it is associated with mineralization processes occurring in Cretaceous sedimentary rocks (sandstones). ## Mineral Associations This mineral co-occurs with other selenides. It is most commonly found as inclusions in umangite. It is also accompanied by klockmannite, clausthalite, watkinsite, chalcomenite, as well as hematite and siderite. ## Localities The only confirmed and described occurrence of quijarroite worldwide is its type locality – the El Dragón mine, in Antonio Quijarro Province, Potosí Department, Bolivia.

Rarity

Extremely rare

For collectors

## Quality Criteria Quijarroite is a mineral of purely scientific interest and for highly specialized collectors ("micromounters"). As it does not form macroscopic crystals, its collector's value is negligible. The most valuable samples are those where the mineral has been unequivocally identified and analytically documented, originating from the type locality. The visual appeal of a specimen depends on the quality of the associated minerals, primarily umangite.

Care and storage

## Cleaning Specimens containing quijarroite, due to its microscopic nature and occurrence as inclusions, generally do not require and should not be subjected to mechanical or chemical cleaning. Any attempt at cleaning may damage the associated minerals and quijarroite itself. It is best to leave the specimen in its untouched state. ## What to Avoid Avoid contact with any chemicals, acids, and cleaning agents. Also, protect the specimen from ultrasound, high temperatures, and sudden temperature changes. Due to the presence of mercury and selenium, avoid inhaling dust and wash hands after handling the specimen. ## Storage Specimens should be stored under stable conditions, in a closed collector's box, to protect them from dust and mechanical damage. Storage in darkness is not necessary, but prolonged exposure to intense light is not recommended.

Sources

IMA Mineral List (CNMNC)