Meurigite-Na

Chemical formula: [Na(H₂O)₂.₅][Fe₃+₈(PO₄)₆(OH)₇]·₄H₂O

A rare iron phosphate, forming characteristic, silky aggregates of acicular crystals with an intense yellow color.

## Characteristics Meurigite-Na is a hydrated sodium and iron phosphate, belonging to the meurigite group. It occurs as delicate, acicular crystals gathered in spherical or radial aggregates, as well as in bundles, coatings, and crusts. Its most characteristic features are its intense, golden-yellow color and silky luster, which give specimens an attractive appearance. Individual crystals are usually very small and visible only under magnification, but their dense aggregates can cover significant areas of the host rock. ## Physical Properties This mineral is relatively soft, with a hardness of about 3 on the Mohs scale, making it susceptible to scratching. Its crystals are brittle and easily damaged. The luster is most often silky, especially in dense, fibrous aggregates, and can also be vitreous on single, better-formed crystals. It is a translucent mineral. The calculated density is approximately 2.96 g/cm³. ## Colors and Varieties Meurigite-Na occurs in shades from pale yellow, through intense golden-yellow, to yellowish-brown. It does not form color varieties, and its name indicates that it is an analog of meurigite-K, in which sodium dominates over potassium in the crystal structure. ## History and Name The name "meurigite" honors the Welsh mineral collector, Sir Meurig Williams (1928–1993). The suffix "-Na" was added to distinguish it from the original meurigite (now meurigite-K), in accordance with the naming rules for minerals of this group. The original mineral (meurigite-K) was described in 1996. ## Applications Due to its rarity and small crystal size, meurigite-Na has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 3
Luster: Silky to Vitreous
Streak: Pale yellow
Density: 2.96
Cleavage: Perfect on {010}
Fracture: Fibrous
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The most important features allowing the identification of meurigite-Na are its characteristic habit in the form of radial, fibrous aggregates, intense golden-yellow color, and silky luster. It occurs as a secondary mineral in paragenesis with other phosphates. ## Distinguishing from Similar Minerals Meurigite-Na is sometimes confused with other secondary yellow phosphates. It is distinguished from cacoxenite by its usually lighter, more golden hue (cacoxenite can be more orange or brownish). Beraunite and rockbridgeite, with which it co-occurs, usually have darker, greenish or brownish colors. A definitive distinction from the very similar meurigite-K is almost exclusively possible through chemical analysis (e.g., EDS). ## Crystal Forms Crystals are strongly elongated, acicular or hair-like. They almost always form aggregates: radial aggregates resembling spheres or fans, dense, tangled masses with a felt-like structure, as well as crusts and coatings on other minerals.

Geological environment

## Genesis Meurigite-Na is a secondary mineral, forming in the oxidation zones of ore deposits or in phosphate-rich pegmatites. It forms as a result of weathering and alteration of primary phosphate minerals, such as triphylite, in the presence of iron- and sodium-rich solutions. It can also crystallize as a product of post-mining activity on dumps and in old workings. ## Mineral Associations It often co-occurs with other secondary phosphate minerals, such as strengite, phosphosiderite, rockbridgeite, dufrénite, beraunite, cacoxenite, as well as with iron oxides and hydroxides, mainly goethite. ## Localities Significant localities of meurigite-Na worldwide include the Fuchsbau quarry in Fichtelgebirge, Bavaria (Germany), the Santa Rosa mine in Itinga, Minas Gerais (Brazil), where high-quality collector specimens were found, and the Nagasumi quarry in Ehime Prefecture (Japan). It also occurs in some pegmatites in the Black Hills region of South Dakota (USA).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, radial aggregates of intense, golden-yellow color. The size and richness of the aggregates on a contrasting rock matrix are also highly rated. Due to the mineral's fragility, the absence of damage to the delicate, acicular crystals is crucial. Specimens from classic localities, such as Santa Rosa or Fuchsbau, are particularly sought after. ## Popular Localities The best localities for this mineral are considered to be in Brazil (Santa Rosa mine) and Germany (Fuchsbau quarry), from which many reference specimens originate. Attractive micromounts have also been obtained in Japan (Nagasumi) and the USA (Black Hills).

Care and storage

## Cleaning Meurigite-Na specimens are very delicate and should be handled with care. To remove dust, it is best to use a soft brush or compressed air from a safe distance. Due to its hydrated nature, prolonged contact with water should be avoided. If washing is necessary, use distilled water and dry the specimen as quickly as possible. ## What to Avoid The mineral is susceptible to mechanical damage, so ultrasonic cleaning, scrubbing, and impacts should be avoided. It should be protected from contact with acids and other chemicals. Prolonged exposure to moisture can lead to its degradation. ## Storage It is recommended to store specimens in closed, padded boxes (such as "membrane boxes" or display cases) to protect them from dust, moisture, and physical damage. Brittle, acicular aggregates are easily broken, so avoid touching their surfaces.

Sources

IMA Mineral List (CNMNC)