Miguelromeroite

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

Miguelromeroite is a rare, hydrated manganese arsenate, forming characteristic, radiating aggregates of an intense, red-orange color.

## Characteristics Miguelromeroite is an arsenate mineral belonging to the hureaulite group. It forms elongated, prismatic or bladed crystals, most commonly occurring as radiating or fan-shaped aggregates, as well as spherical clusters. Its most distinctive feature is its intense, vivid color, ranging from red-orange to brownish-red, which makes it a recognizable and prized specimen. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its hardness on the Mohs scale is 3 to 4, classifying it as a relatively soft mineral. The density of miguelromeroite is approximately 3.45 g/cm³. ## Colors and Varieties The dominant and virtually sole color range for this mineral includes shades of red and orange, from bright red-orange to a deeper, brownish-red. No color varieties or commercial varieties are distinguished. ## History and Name Miguelromeroite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2007. Its name honors Miguel Romero Sánchez (1928–2006), a distinguished Mexican mineral collector, for his contribution to the preservation of Mexico's mineralogical heritage. The type locality (locus typicus) is the Veta Negra mine in the Atacama Region, Chile. ## Uses Due to its rarity and small accumulations, miguelromeroite has no industrial applications. It is solely an object of scientific interest and a valued acquisition in advanced collections of rare minerals.

Properties

Mohs hardness
3-4
Luster
Vitreous
Streak
Light reddish-brown
Density
3.45
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key features for identifying miguelromeroite are its unique red-orange color, radiating or spherical aggregates, and vitreous luster. Hardness (3-4) and relatively high density are also helpful. Occurrence in paragenesis with other rare arsenates in oxidized zones of polymetallic deposits is a strong indicator. ## Distinguishing from Similar Minerals Miguelromeroite is sometimes confused with other colorful arsenates. It is distinguished from erythrite by its orange-red, rather than pinkish-purple, color and its association with manganese, not cobalt. It differs from pharmacosiderite in crystal habit (prismatic, not isometric) and aggregate form. Geological context and associated minerals are crucial for correct identification. ## Crystal Forms Crystals are prismatic to bladed, almost always gathered into characteristic, radiating aggregates resembling fans, rosettes, or complete spheres. Single, well-formed crystals are extremely rare.

Geological environment

## Genesis Miguelromeroite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal polymetallic deposits. It crystallizes as a result of alterations of earlier arsenic- and manganese-bearing minerals under conditions of low temperatures and pressures. ## Mineral Associations It most commonly co-occurs with other, often rare, manganese and calcium arsenates, such as picropharmacolite, villyaellenite, sainfeldite, as well as with manganese oxides (cryptomelane, hollandite) and quartz. ## Localities The most important and well-known worldwide locality, from which the best specimens originate, is the Veta Negra mine in Pampa Larga, Copiapó Province (Atacama Region, Chile). It is also known from several other localities worldwide, including the Gozaisho mine in Japan, but specimens from there are much rarer and usually of lower quality.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized miguelromeroite specimens are characterized by an intense, saturated, red-orange color. The form of the aggregates is crucial – ideal, complete spheres or symmetrical "fans" with sharp, undamaged crystals command the highest prices. The size of the aggregates and the aesthetic contrast with a light matrix rock are also important. ## Popular Localities By far the most desirable and well-known source of collector specimens is the type locality – the Veta Negra mine in Chile. Specimens from this location are considered the global standard for this mineral.

Care and storage

## Cleaning Miguelromeroite specimens should be cleaned with great care, preferably dry, using a soft brush or compressed air. Brief rinsing in distilled water is permissible, after which the specimen should be immediately and thoroughly dried. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to high temperatures, which can lead to its dehydration (loss of water from the crystal lattice) and structural damage. Contact with acids and other chemicals should be avoided. As an arsenate, it is toxic – hands should be thoroughly washed after any contact with the mineral. ## Storage It is recommended to store specimens in stable conditions, in closed boxes or display cases, away from direct sunlight and heat sources. Its low hardness makes it susceptible to scratching, so it should be stored separately from harder minerals.

External references

Sources

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