Madeiraite

Chemical formula: Na<sub>2</sub>Ca<sub>2</sub>Fe<sup>2+</sup><sub>2</sub>Zr<sup>4+</sup><sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>O<sub>2</sub>F<sub>2</sub>

Madeiraite is a very rare sorosilicate mineral, discovered on the Portuguese island of Madeira, from which it takes its name.

## Characteristics Madeiraite is an extremely rare mineral belonging to the sorosilicate group and the wöhlerite supergroup. It occurs as very small, tabular or bladed crystals, reaching up to 0.3 mm in size. It typically forms radial aggregates or appears as single crystals embedded in rock. Its small size makes it an object of interest primarily for specialized micromineral collectors. ## Physical Properties Madeiraite crystals exhibit a vitreous luster. The mineral is transparent to translucent. Due to the small size of the crystals, precise determination of hardness and density is difficult, but based on its composition and structure, these can be estimated as typical for silicates. ## Colors and Varieties Madeiraite is characterized by a pale yellow to yellowish-brown color. No pleochroism has been observed. No named varieties of this mineral are recognized. ## History and Name The mineral was discovered in the Água de Pau volcanic massif on São Miguel Island in the Azores archipelago (Portugal), and not, as its name might suggest, on Madeira. However, the name "madeiraite" was given in honor of the Madeira archipelago, a location with a similar geological structure. It was officially approved by the International Mineralogical Association (IMA) in 2007 (IMA2007-030). It was described by an international team of researchers led by Alexander R. Chakhmouradian. ## Uses Madeiraite has no industrial application. Its significance is purely scientific and collectible, as a unique representative of its mineralogical group.

Properties

Mohs hardness
5.5-6
Luster
Vitreous
Streak
White
Density
3.44
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of madeiraite is practically impossible due to its microscopic size and occurrence as inclusions. Definitive identification requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) combined with X-ray diffraction (XRD), which allow for the determination of chemical composition and crystal structure. ## Differentiation from Similar Minerals Madeiraite can be confused with other rare zirconium silicates from the wöhlerite supergroup, such as wöhlerite, lavenite, or hiortdahlite, which may occur in similar geological environments and have a similar color. Differentiation is possible only through precise analysis of chemical composition, especially the content of sodium, calcium, iron, and fluorine. ## Crystal Forms Madeiraite forms very small, thin, tabular or bladed crystals, often flattened parallel to the {100} plane. These crystals typically combine into radial or stellate aggregates.

Geological environment

## Genesis Madeiraite is a mineral of magmatic origin. It forms in the late stages of crystallization within highly differentiated, silica-undersaturated alkaline rocks, such as nepheline syenites. It crystallizes in vugs and miarolitic cavities within these rocks. ## Mineral Associations This mineral co-occurs with other minerals typical of advanced crystallization stages of nepheline syenites. In its type locality (Água de Pau), it was found in association with aegirine, nepheline, sodalite, eudialyte, astrophyllite, lorenzenite, and fluorite. ## Localities The only confirmed and described locality for madeiraite in the world is its type locality: the Água de Pau volcanic massif on São Miguel Island, Azores, Portugal. It is an endemic mineral to this location.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a madeiraite specimen is primarily assessed based on the richness and development of crystals within the aggregate. The most desirable specimens are those with clearly visible, sharp, radial clusters of an intense, yellowish-brown color. Contrast with the surrounding rock (matrix) and the presence of rare associated minerals are also important. ## Popular Localities The only source of madeiraite specimens is its type locality in the Azores, Portugal. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Madeiraite specimens, due to their extreme rarity and small size, should be cleaned with the utmost care. It is recommended to use compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a very soft brush, avoiding any mechanical pressure. ## What to Avoid Avoid contact with any chemicals, including acids and strong bases. Do not subject specimens to ultrasonic cleaning. The mineral should be protected from sudden temperature changes and prolonged exposure to intense sunlight, which could theoretically affect its color. ## Storage Madeiraite specimens, as microminerals, are best stored in specialized "micromount" boxes, which protect them from dust, mechanical damage, and humidity. Display should be in stable room conditions.

Sources

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