Whitmoreite

Chemical formula: Fe²⁺Fe³⁺₂(PO₄)₂(OH)₂·4H₂O

Whitmoreite is a rare phosphate mineral, forming radial, acicular crystal aggregates with a characteristic dark brown to almost black color.

## Characteristics Whitmoreite is a hydrated iron phosphate belonging to the arthurite group. It forms characteristic radial or stellate aggregates composed of very fine, acicular or bladed crystals. Individual crystals rarely reach significant sizes, and entire aggregates typically range from a few to a dozen millimeters in diameter. This mineral is valued by collectors for its spectacular, radial forms. ## Physical Properties Whitmoreite crystals exhibit a luster ranging from vitreous to adamantine. They are brittle and translucent, and on thin edges, they can be almost transparent. The Mohs hardness is approximately 3, and the density ranges between 3.16 and 3.20 g/cm³. ## Colors and Varieties This mineral occurs in shades from dark brown and brownish-green to almost black. It sometimes exhibits a delicate pleochroism in shades of brown and green. No distinct color varieties or commercial varieties are recognized. ## History and Name Whitmoreite was first described in 1974 by Paul B. Moore, Anthony R. Kampf, and Anthony J. Irving. The mineral is named in honor of Robert W. Whitmore (1905-1979), an American mining engineer and mineral collector from New Hampshire, who first found this mineral in the Palermo No. 1 mine. ## Uses Whitmoreite has no industrial application. It is solely a mineral of scientific and collecting interest.

Properties

Mohs hardness
3
Color
Yellow-brown, green-brown
Luster
Vitreous to adamantine
Streak
Light brown
Density
2.87
Cleavage
Fair on {100}
Fracture
Uneven
Transparency
Transparent,Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The most characteristic feature of whitmoreite is its radial or stellate aggregates of fine, acicular crystals with a dark brown color. The luster, ranging from vitreous to adamantine, is also helpful in identification. It occurs in paragenesis with other secondary phosphates in granitic pegmatites. ## Distinguishing from Similar Minerals Whitmoreite can be confused with other minerals from the arthurite group or similar secondary iron phosphates, such as laueite or strunzite, which can form similar aggregates. Distinguishing it from these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). Geological context and associated minerals can be a crucial clue. ## Crystal Forms Crystals are prismatic, elongated, and often flattened, forming bladed or acicular shapes. They typically occur in radial, spherical, or hemispherical aggregates, as well as rosettes and fans. Single, well-formed crystals are less common.

Geological environment

## Genesis Whitmoreite is a secondary phosphate mineral that forms as a result of hydrothermal alteration or weathering of primary phosphates (mainly triphylite) in the oxidation zones of complex granitic pegmatites. It crystallizes in rock cavities and fissures. ## Mineral Associations This mineral often co-occurs with other phosphates, such as siderite, triphylite, ludlamite, strunzite, laueite, beraunite, rockbridgeite, jahnsite, quartz, and mitridatite. This paragenesis is typical for phosphate pegmatites. ## Localities The most important and classic locality (type locality) is the Palermo No. 1 mine in North Groton, New Hampshire, USA. This mineral has also been found in other pegmatites in the USA (e.g., in the Big Chief and Etta mines in South Dakota). Outside the United States, its occurrence has been confirmed in a few localities, including the Sapucaia mine in Brazil and the Hagendorf-Süd pegmatite in Germany.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued by collectors are specimens with well-defined, spherical or stellate aggregates of intense, dark brown color. High crystal luster and contrast with the light matrix rock are important. Specimens where the radial aggregates are complete, undamaged, and clearly separated from each other fetch higher prices. The size of the aggregates also matters, although even small but aesthetic aggregates are sought after. ## Popular Localities By far the most desirable and classic specimens come from the type locality – the Palermo No. 1 mine in New Hampshire, USA. Material from this location is considered exemplary for the species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to its brittleness and potential reactivity, washing with water, and especially with chemical agents, should be avoided. If it is necessary to remove loose contaminants, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The mineral is brittle, so it must be protected from impacts, vibrations, and falls. It should not be heated or exposed to prolonged strong sunlight. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust, mechanical damage, and sudden changes in humidity. It is best to keep it away from other, harder minerals that could scratch it.

External references

Sources

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