Bobshannonite

Chemical formula: Na₂KBa(Mn₂+,Na)₈(Nb₅+,Ti₄+)₄(Si₂O₇)₄O₄(OH)₄(O,F)₂

Bobshannonite is a rare mineral from the seidozerite group, characterized by its complex chemical composition and occurrence as dark, tabular crystals.

## Characteristics Bobshannonite is a very rare and complex silicate from the seidozerite group. It forms small, tabular or lath-like crystals, usually not exceeding 1 mm in length. It most often occurs as aggregates or clusters. Its color ranges from dark brown to almost black, and it can be translucent brown on thin edges. It is an opaque to translucent mineral. ## Physical Properties The mineral is characterized by a Mohs hardness of 4. It has a vitreous luster and a density of 3.65 g/cm³. It exhibits perfect cleavage in one direction. Its streak is light brown. ## History and Name Bobshannonite was first described in 2014. Its name honors Robert (Bob) D. Shannon (born 1935), an American crystal chemist and retired DuPont scientist, for his fundamental contributions to the study of ionic radii and their application in mineralogy and inorganic chemistry. The discovery was made on material from the Poudrette quarry at Mont Saint-Hilaire, Quebec, Canada.

Properties

Mohs hardness: 4
Luster: Vitreous
Streak: Light brown
Density: 3.65
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Triclinic

Diagnostic features

## Identification Identifying bobshannonite under amateur conditions is practically impossible. It requires advanced analytical techniques, such as X-ray diffraction (XRD) and chemical analysis (e.g., EDS/WDS), due to its complex composition and similarity to other rare minerals from Mont Saint-Hilaire. ## Differentiation from similar minerals It can be confused with other dark minerals from the seidozerite and lamprophyllite groups, such as jinshajiangite, perraultite, or lamprophyllite. Differentiation relies solely on detailed chemical and crystallographic analysis. ## Crystal forms Bobshannonite forms flattened, tabular or lath-like crystals, often grouped into rosette-like or radial aggregates.

Geological environment

## Genesis Bobshannonite occurs in sodalite syenite xenoliths within a nepheline syenite intrusive complex. It formed in the late stage of hydrothermal processes, crystallizing in rock cavities and fractures. ## Mineral associations This mineral coexists with aegirine, albite, microcline, nepheline, sodalite, eudialyte, catapleiite, sérandite, steacyite, as well as other rare minerals like perraultite and jinshajiangite. ## Localities The only confirmed occurrence of bobshannonite in the world is its type locality – the Poudrette quarry, located at Mont Saint-Hilaire, in the Montérégie region of Quebec, Canada.

Rarity

Extremely rare

For collectors

## Quality criteria As a mineral of primarily scientific and systematic importance, every specimen is valuable. The most desirable ones are those with well-formed, sharp crystals, even if microscopic. Aesthetic composition with other well-defined associated minerals, typical for this locality, is also important. ## Popular localities The only source of specimens is the Poudrette quarry at Mont Saint-Hilaire (Quebec, Canada), which is world-renowned for hundreds of unique and rare mineral species.

Care and storage

## Cleaning Due to its rarity and potential fragility, cleaning should be kept to an absolute minimum. If necessary, compressed air can be used to remove dust. Contact with water and any chemical agents should be avoided. ## What to avoid Avoid ultrasonic cleaners, steam cleaning, acids, and detergents. The mineral should be protected from sudden temperature changes and direct, prolonged exposure to sunlight, although its specific light sensitivity is not known. ## Storage Bobshannonite specimens, being extremely rare and usually microscopic, should be stored under stable conditions, preferably in sealed "micromount" boxes. This protects them from dust, mechanical damage, and sudden changes in humidity.

Sources

IMA Mineral List (CNMNC)