Bostwickite

Chemical formula: CaMn<sup>3+</sup><sub>6</sub>Si<sub>3</sub>O<sub>16</sub>·7H<sub>2</sub>O

Bostwickite is a very rare hydrated calcium manganese silicate, forming microscopic, dark red crystals and coatings.

## Characteristics Bostwickite is a very rare mineral from the silicate group, occurring as microscopic, bladed or acicular crystals. It typically forms rosetted aggregates, spherulitic clusters, or thin coatings and efflorescences on other minerals. Its crystals rarely exceed 1 mm in length, making it a mineral primarily accessible to advanced micromount collectors. ## Physical Properties Bostwickite crystals are flexible and exhibit a silky luster. Due to the microscopic size of the crystals, determining hardness and density is difficult; hardness is estimated at approximately 1 on the Mohs scale, and the calculated density is 2.93 g/cm³. It is transparent to translucent. ## Colors and Varieties This mineral is characterized by an intense, dark red to reddish-brown color. No color varieties or commercial varieties are known. ## History and Name Bostwickite was discovered in the Sterling Hill mine in Ogdensburg, Sussex County (New Jersey, USA) and described in 1983 by Pete J. Dunn and Ronald C. Ramik. The mineral is named in honor of Richard C. Bostwick (born 1942), an American mineral collector specializing in fluorescent minerals, who first noticed this mineral.

Properties

Mohs hardness
1
Luster
Silky
Streak
Red
Density
2.93
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Bostwickite is identified by its characteristic appearance – small, acicular or bladed crystals of an intense, dark red color, forming rosetted aggregates. Key to identification are the locality (Franklin and Sterling Hill mines) and associated minerals. ## Differentiation from similar minerals It can be confused with other rare, red manganese silicates from this locality, such as ruizite. Ruizite has a brighter, orange-red color and crystallizes in the monoclinic system, while bostwickite is darker and crystallizes in the orthorhombic system. Final differentiation requires advanced analytical methods (XRD, EDS). ## Crystal forms It forms elongated, bladed or acicular crystals, often flattened. These crystals combine into radial, rosetted, or spherulitic aggregates, and also form thin coatings on the surface of the host rock.

Geological environment

## Genesis Bostwickite is a secondary mineral, formed by hydrothermal processes in metamorphically altered zinc, iron, and manganese deposits. It forms in fractures and on rock cleavage surfaces. ## Mineral associations It most commonly co-occurs with calcite, franklinite, willemite, andradite, barite, cupriferous cuprite, tenorite, and other rare manganese minerals such as ruizite and orientite. ## Localities Bostwickite is known almost exclusively from two adjacent localities worldwide: the Sterling Hill mine in Ogdensburg and the Franklin mine in Franklin, Sussex County, New Jersey, USA. These are classic localities for many rare minerals.

Rarity

Very rare

For collectors

## Quality criteria As a "micromount" type mineral, the quality of a specimen is primarily determined by the richness and aesthetics of the aggregates. The most prized specimens are those with distinct, well-formed, radial crystal groups of an intense red color, contrasting with a light background of the host rock (e.g., with white calcite). The size of individual aggregates and the surface coverage also significantly influence the value. ## Popular localities The best and practically only specimens come from historical finds in the Sterling Hill and Franklin mines in New Jersey, USA. Specimens from these localities are the standard for this mineral.

Care and storage

## Cleaning Due to the extreme delicacy and small size of the crystals, mechanical cleaning is not recommended and can damage the specimen. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water and chemicals. ## What to avoid Avoid any contact with water, acids, bases, and organic solvents. The mineral is very soft and brittle, so it must be protected from shocks, friction, and any pressure. It should not be heated or exposed to ultrasound. ## Storage Bostwickite specimens should be stored exclusively in dedicated, sealed "micromount" boxes that protect them from dust and mechanical damage. Avoid exposure to direct sunlight and store in a location with stable, low humidity.

Sources

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