Tomcampbellite

Chemical formula: [KCl][Fe<sup>2+</sup><sub>14</sub>(OH)<sub>6</sub>(PO<sub>4</sub>)<sub>6</sub>(PO<sub>3</sub>OH)<sub>2</sub>]

Tomcampbellite is a rare phosphate mineral, forming aggregates of fine, tabular crystals with a characteristic dark green color.

## Characteristics Tomcampbellite is a complex hydrated iron, potassium, and chlorine phosphate, occurring as very fine, tabular or bladed crystals. It typically forms dense, felted aggregates or rosette-like clusters with an intense, dark green to almost black color. Individual crystals rarely exceed 1 mm in length, making their observation require magnification. ## Physical Properties Tomcampbellite crystals exhibit a vitreous luster. They are transparent to translucent. Due to the small size of the crystals, hardness and density have not been precisely determined, but based on their composition, they can be estimated as moderately hard and relatively dense. ## Colors and Varieties This mineral is monochromatic – it occurs exclusively in shades of dark green, often so saturated that it appears black. No varieties have been distinguished. ## History and Name Tomcampbellite was discovered in the Palermo No. 1 mine in Grafton County, New Hampshire (USA) and described in 2018. Its name honors Thomas (Tom) J. Campbell, a geology professor and mineral collector, for his contributions to pegmatite mineralogy. ## Uses Tomcampbellite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals, systematics, or minerals from granitic pegmatites.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Light green
Density
3.23
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Tomcampbellite is identified by its characteristic appearance – dark green, rosette-like or felted aggregates of fine, tabular crystals. Key to identification is its occurrence (granitic pegmatites) and co-occurrence with other rare phosphates. ## Differentiation from Similar Minerals It can be confused with other dark green phosphates, such as vivianite or rockbridgeite. Differentiation requires analysis of crystal habit (tomcampbellite forms thin tablets, often in rosettes) and advanced research methods, such as Raman spectroscopy or X-ray diffraction (XRD), which are essential for certain identification. ## Crystal Forms Crystals are very small, thin, and tabular, with a hexagonal or bladed outline. Most often they occur as dense, radial or rosette-like aggregates, as well as felted masses covering other minerals.

Geological environment

## Genesis Tomcampbellite is a secondary mineral, formed in the late stages of hydrothermal processes in complex granitic pegmatites. It crystallizes in vugs and fissures, often on the surface of previously crystallized minerals. ## Mineral Associations This mineral co-occurs with other phosphates, such as strengite, phosphosiderite, rockbridgeite, as well as with quartz, albite, and muscovite. Its presence is an indicator of specific chemical conditions prevailing in the final stage of pegmatite evolution. ## Localities The only confirmed and described locality of tomcampbellite in the world is its type locality – the Palermo No. 1 mine in North Groton, Grafton County, New Hampshire, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with clearly formed, undamaged rosettes of crystals, contrastingly set on a light rock matrix (e.g., on quartz or albite). The size of the aggregates and the intensity of the green color also affect the attractiveness of the specimen. Due to the nature of the mineral, crystal clarity is not a key criterion. ## Popular Localities The only source of collector specimens is the historic type locality in New Hampshire, USA. Material from this mine is very limited and sought after by specialists.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the delicacy and small size of the crystals, contact with water, especially ultrasonic cleaners, is absolutely inadvisable. ## What to Avoid Avoid all chemicals, acids, and detergents, which can damage or dissolve the fine crystals. The mineral may be sensitive to sudden temperature changes. It should not be exposed to prolonged strong sunlight. ## Storage Tomcampbellite specimens, as microminerals, are best stored in specialized "micromount" boxes, which protect them from dust, mechanical damage, and direct contact. Display should be in stable room conditions.

Sources

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