Dickinsonite-(KMnNa)

Chemical formula: K(NaMn₂+)CaNa₃AlMn₂+₁₃(PO₄)₁₂(OH)₂

Dickinsonite-(KMnNa) is a very rare phosphate mineral, occurring as small, platy crystals of a greenish color.

## Characteristics Dickinsonite-(KMnNa) is a complex phosphate belonging to the arrojadite group. It forms very small, most often microscopic, platy or bladed crystals, rarely exceeding 1 mm in length. They usually occur as radial or chaotically arranged aggregates. The mineral is characterized by a vitreous luster and a color ranging from pale green to greenish-yellow. ## Physical Properties The mineral has a hardness of 3.5-4 on the Mohs scale. It has a vitreous luster and is transparent to translucent. It exhibits perfect cleavage in one direction. ## Colors and Varieties The observed colors of dickinsonite-(KMnNa) are mainly shades of green - from pale green to greenish-yellow. Due to its extreme rarity, no commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition - it is a member of the dickinsonite group, in which potassium (K), manganese (Mn), and sodium (Na) are the dominant cations in specific structural positions. It was formally described as a new mineral in 2006 by Ian E. Grey and co-workers based on material from the original dickinsonite locality. ## Uses Dickinsonite-(KMnNa) has no industrial applications. Its significance is purely scientific and collectible, being a coveted object for specialized collectors of rare minerals (so-called "micromounts").

Properties

Mohs hardness: 3.5-4
Luster: Vitreous
Streak: Pale greenish white
Density: 3.43
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification under collecting conditions is extremely difficult and relies on visual analysis under a microscope. Key features include the form of small, platy crystals, greenish color, vitreous luster, and co-occurrence with other rare phosphates in granitic pegmatites. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals This mineral can be confused with other rare, green phosphates found in pegmatites, such as other minerals from the arrojadite or dickinsonite group. "On-the-fly" differentiation is practically impossible without specialized equipment. ## Crystal Forms Crystals are very small, platy or bladed, often flattened. They form radial or irregular aggregates and clusters on the surface of other minerals.

Geological environment

## Genesis Dickinsonite-(KMnNa) is a hydrothermal mineral, crystallizing in the late stages of the evolution of complex granitic pegmatites, rich in phosphorus, lithium, and sodium. It forms as a result of metasomatism and alteration of primary phosphates, such as triphylite. ## Mineral Associations This mineral co-occurs with other pegmatitic phosphates, such as eosphorite, fairfieldite, vivianite, as well as with quartz, albite, and muscovite. ## Localities The only confirmed and described occurrence of this mineral in the world is the Branchville quarry in Branchville, Fairfield County, Connecticut, USA. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity and microscopic size, the main quality criterion is the mere presence of the identified mineral on the rock matrix. Specimens with better-formed crystals, richer clusters, and clear visibility against other minerals are more highly valued. A contrasting matrix enhances the visual appeal of the specimen under the microscope. ## Popular Localities The only source of specimens is the historical type locality - the Branchville quarry in Connecticut, USA. Material from this location is highly prized by specialized collectors.

Care and storage

## Cleaning Specimens should be handled with utmost care. Cleaning is generally not recommended due to the delicacy and small size of the crystals. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and all forms of mechanical cleaning (e.g., brushes). The mineral is brittle and has perfect cleavage, making it susceptible to damage. ## Storage It is recommended to store specimens exclusively in specialized, sealed micromount boxes to protect them from dust, shocks, and mechanical damage. Display should only be done under a microscope.

Sources

IMA Mineral List (CNMNC)