Hureaulite

Chemical formula: Mn<sup>2+</sup><sub>5</sub>(PO<sub>4</sub>)<sub>2</sub>(PO<sub>3</sub>OH)<sub>2</sub>·4H<sub>2</sub>O

Hureaulite is a hydrated manganese phosphate, forming characteristic, vitreous crystals with colors ranging from pink and orange to reddish-brown.

## Characteristics Hureaulite is a hydrated manganese phosphate, valued by collectors for its well-formed crystals with vibrant colors. It typically forms short, prismatic or tabular crystals, often grouped into radial, fan-shaped, or nearly spherical aggregates. It can also occur as granular or massive masses. Its crystals can be transparent to translucent, with an attractive, vitreous luster. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5. It is quite brittle, and its density ranges from 3.16 to 3.29 g/cm³. The luster is vitreous, and on fracture surfaces, it can be somewhat resinous. Some specimens may exhibit weak, greenish-yellow fluorescence under ultraviolet light. ## Colors and Varieties The color spectrum of hureaulite is wide and includes shades from pale pink, through yellow, orange, reddish, to brown and reddish-brown. The coloration primarily depends on the manganese content and its oxidation state. No formal varieties of this mineral are distinguished, and classification is mainly based on color and aggregate form. ## History and Name The name hureaulite comes from its first discovery site in 1825 – the Les Hureaux quarry in the town of Saint-Sylvestre in the Limousin region of France. The mineral was described by the French mineralogist François-Sulpice Beudant. ## Uses Hureaulite has no industrial significance. It is a mineral of purely scientific and collector interest, sought after for its attractive crystals and diversity of forms.

Properties

Mohs hardness
3.5
Luster
Vitreous, Resinous
Streak
White
Density
3.16-3.29
Cleavage
Good on {100}, poor on {010}
Fracture
Uneven, Subconchoidal
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of hureaulite include its monoclinic, often prismatic crystals, grouped into radial or fan-shaped aggregates. Its vitreous luster and colors in shades of pink, orange, and red are also typical. Its occurrence in granitic pegmatites in association with other manganese phosphates is a strong diagnostic indicator. ## Distinguishing from Similar Minerals It can be confused with other phosphates of similar coloration, such as strengite, phosphosiderite, or rhodonite. It differs from strengite and phosphosiderite in crystal habit (strengite and phosphosiderite crystallize in the monoclinic system but often form different aggregates, e.g., reniform). It is distinguished from rhodonite (a silicate) by its lower hardness (3.5 versus 5.5-6.5 for rhodonite) and typical occurrence environment. ## Crystal Forms Hureaulite crystals are monoclinic, usually short, prismatic, often with a rich number of faces. It commonly forms radial aggregates, rosettes, fans, as well as granular and massive masses. Crystals can be twinned.

Geological environment

## Genesis Hureaulite is a secondary mineral, forming in the oxidation zones of manganese-bearing deposits. It most commonly forms as a result of hydrothermal alteration of primary phosphates, such as triplite, in granitic pegmatites. It can also form in sediments rich in manganese and phosphorus. ## Mineral Associations It often co-occurs with other phosphate minerals, such as strengite, phosphosiderite, rockbridgeite, stewartite, as well as with quartz, muscovite, albite, and manganese oxides (e.g., goethite). ## Localities The classic locality is Hureaux in France. Beautiful, well-formed crystals come from pegmatites in Brazil (Sapucaia, Cigana, Jocão mines in Minas Gerais state). Significant specimens have also been found in the USA (Tip Top mine in South Dakota; Newport in New Hampshire), Portugal (Mangualde), Germany (Hagendorf), Namibia (Clementine II mine), and Rwanda.

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued hureaulite specimens are characterized by large, well-formed, transparent crystals with an intense orange or reddish-orange color. The aesthetic appeal is enhanced by beautifully formed, radial aggregates set on a contrasting rock matrix. Crystal clarity and the absence of mechanical damage are also important. ## Market Prices Hureaulite prices vary. Small, single crystals or miniature clusters can be purchased for several tens to several hundreds of Polish zlotys. High-grade specimens from classic localities, with large, gemmy crystals on matrix, can fetch prices from several hundred to several thousand US dollars, depending on quality and aesthetics. ## Popular Localities Specimens from Brazilian pegmatites in Minas Gerais, especially from the Sapucaia and Cigana mines, are considered among the best in the world. Historical specimens from France and large crystals from the Tip Top mine in the USA are also highly prized.

Care and storage

## Cleaning Hureaulite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen should be immediately and thoroughly dried. ## What to Avoid The mineral is sensitive to acids, which can damage it. Ultrasonic cleaners and steam cleaning should be avoided. As a hydrated mineral, it is sensitive to high temperatures, which can lead to dehydration, color change, and loss of luster. It should also be protected from prolonged exposure to direct sunlight. ## Storage Due to its low hardness and brittleness, hureaulite should be stored separately in a padded box to prevent scratches and mechanical damage. It should not come into contact with harder minerals. It is best displayed in a closed cabinet, protected from dust and sudden temperature changes.

External references

Sources

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