Whiteite-(MnFeMg)

Chemical formula: Mn<sup>2+</sup>Fe<sup>2+</sup>Mg<sub>2</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>4</sub>(OH)<sub>2</sub>·8H<sub>2</sub>O

A rare mineral from the jahnsite group, a hydrated phosphate forming tabular crystals and rosettes in granitic pegmatites.

## Characteristics Whiteite-(MnFeMg) is a complex, hydrated phosphate belonging to the jahnsite group. It forms characteristic, well-developed tabular crystals, often aggregated into visually attractive rosettes or fan-like clusters. Crystals are typically small, measuring a few millimeters. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is 4, making it relatively soft and susceptible to scratching. The density is estimated at approximately 2.75 g/cm³. It exhibits good cleavage in one direction. ## Colors and Varieties The most common colors are shades of brown and yellow – from light yellow, through honey-brown, to dark brown. It is less commonly colorless. The name Whiteite-(MnFeMg) precisely defines the chemical variety in which manganese, iron, and magnesium dominate specific positions in the crystal structure. ## History and Name The name "whiteite" was given in honor of John Sampson White (born 1933), an American mineralogist and long-time curator of the mineralogical collection at the Smithsonian Institution. The suffix -(MnFeMg) was added in accordance with nomenclature rules to accurately define the chemical composition of this particular member of the whiteite subgroup. ## Applications Due to its rarity and small crystal size, whiteite-(MnFeMg) has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collectors of rare phosphate minerals.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
White
Density
2.75
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature is the crystal habit – tabular, often aggregated into characteristic rosettes. Its occurrence environment (granitic pegmatites) and associated minerals, such as other rare phosphates, are also important. ## Distinguishing from Similar Minerals It can be confused with other minerals from the jahnsite and whiteite groups, e.g., whiteite-(CaFeMg) or jahnsite-(CaMnMn). Definitive differentiation of these minerals is almost exclusively possible using advanced analytical methods, such as X-ray microanalysis (EDS/WDS). Visually, it may resemble some other brown pegmatite phosphates, such as laueite or stewartite, but it differs from them in crystal habit. ## Crystal Forms It forms flattened, tabular crystals, often with rectangular or hexagonal outlines. These crystals almost always occur in radial or fan-like aggregates, forming striking rosettes.

Geological environment

## Genesis Whiteite-(MnFeMg) is a secondary mineral. It forms as a result of hydrothermal alteration of primary phosphates, mainly triphylite, in phosphorus-rich zones within complex granitic pegmatites. ## Mineral Associations It often co-occurs with other phosphates, such as laueite, strunzite, rockbridgeite, siderite, as well as minerals from the jahnsite and childrenite-eosphorite groups. The primary mineral from which it forms is usually triphylite. ## Localities The most important and typical locality is the Hesnard pegmatite in Groton, Grafton County, New Hampshire, USA. Significant specimens also come from the Tip Top mine in Custer County, South Dakota, USA. These are the main sources of the best quality specimens of this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with sharp, well-formed rosettes of intense, honey-brown color are most highly valued. The contrast with the rock matrix and the presence of other rare associated minerals are of great importance. The size of the rosettes and the lack of damage are key factors influencing collectible value. ## Popular Localities Two localities in the USA are considered classic and provide the best specimens: the Hesnard pegmatite in New Hampshire and the Tip Top mine in South Dakota. Specimens from these locations are most sought after by collectors specializing in mineral systematics or pegmatite minerals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate crystals and their aggregates. ## What to Avoid As a hydrated mineral, it is sensitive to high temperatures, which can lead to dehydration and structural damage. It should be protected from contact with acids and other strong chemicals. Due to its low hardness (4 on the Mohs scale), it is susceptible to scratching – contact with harder minerals should be avoided. ## Storage It is recommended to store specimens in stable conditions, away from direct sunlight and heat sources. It is best to keep them in a separate, padded box or display case to prevent mechanical damage.

Sources

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