Peterandresenite

Chemical formula: Mn²⁺₄Nb⁵⁺₆O₁₉(H₂O)₁₂·₂H₂O

Peterandresenite is a very rare, orange hydrated manganese niobate, forming small, tabular crystals in syenitic pegmatites.

## Characteristics Peterandresenite is a hydrated manganese niobate that visually manifests as very small, hexagonal or pseudohexagonal crystals with a tabular habit. They typically do not exceed 0.2 mm in diameter and often form rosette-like or radial aggregates. The crystals are transparent and characterized by an intense, orange color and a vitreous luster. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 2.5. Its density, calculated based on the chemical formula and unit cell parameters, is 3.45 g/cm³. The crystals exhibit perfect cleavage in one direction, perpendicular to the longest crystal axis. ## Colors and Varieties The dominant and only observed color of peterandresenite is an intense, pure orange. No color varieties or commercial varieties of this mineral have been described. ## History and Name Peterandresenite was first described in 2012 by Roy

Properties

Mohs hardness: 2-2.5
Color: Orange
Luster: Vitreous
Streak: Pale orange
Density: 3.10
Cleavage: Perfect on {0001}
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The key diagnostic feature of peterandresenite is its intense, orange color, vitreous luster, and occurrence as very small, hexagonal, tabular crystals, often in radial aggregates. Its characteristic reaction to water is also distinctive – contact with water causes the mineral to turn white and opaque. This feature can be observed under a microscope by applying a drop of water. ## Distinguishing from Similar Minerals Due to the unique combination of color, crystal form, and occurrence environment, it is unlikely to be confused with other minerals. Its reactivity with water is almost unique and serves as a decisive distinguishing test. ## Crystal Forms Peterandresenite crystallizes in the form of thin, hexagonal plates. These crystals rarely occur individually, most often forming fan-shaped, radial, or rosette-like aggregates and clusters on the surface of other minerals.

Geological environment

## Genesis Peterandresenite is a secondary mineral, formed by hydrothermal processes in the late stage of syenitic pegmatite crystallization. It forms in rock cavities and fissures as a result of the alteration of earlier niobium minerals. ## Mineral Associations This mineral occurs in association with other rare pegmatitic minerals. In the type locality (AS Granit, Langesundsfjorden), it was found in association with microcline, aegirine, kupletskite, catapleiite, lorenzenite, serandite, and manganoneptunite. ## Localities The only confirmed and described locality of peterandresenite in the world is the AS Granit quarry in the Langesundsfjorden area, Larvik municipality, Norway. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of peterandresenite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. The most desirable specimens are those with clearly formed, radial or rosette-like clusters of intense orange color, contrasting well with the light background of the host rock (most often microcline). Due to the microscopic size of the crystals, their large number and dense surface coverage are crucial. The purity and transparency of individual crystals, visible under magnification, also increase the value of the specimen. ## Popular Localities The only source of specimens, including those of collector quality, is the AS Granit quarry in Norway. All peterandresenite available on the collector's market originates from this single locality.

Care and storage

## Cleaning Peterandresenite specimens should be cleaned only with the utmost care. It is permissible to use a soft brush to remove loose contaminants. Due to its reactivity with water, washing in water, especially tap water, should be avoided. If liquid is necessary, crystals can be very carefully wiped with a cotton swab minimally moistened with pure alcohol or acetone, ensuring rapid evaporation. ## What to Avoid Contact with water must be absolutely avoided, as it causes decomposition and loss of transparency. The mineral is sensitive to atmospheric moisture, so it should not be stored in humid conditions. It should also be protected from acids and other chemicals. It is soft and brittle, making it susceptible to mechanical damage. ## Storage Peterandresenite requires storage in dry conditions. The best solution is a sealed container (a so-called perky box) with a desiccant, such as silica gel. Display should be in a closed cabinet, away from sources of moisture and direct sunlight.