Merrihueite

Chemical formula: (K,Na)₂(Fe²⁺,Mg)₅Si₁₂O₃₀

Merrihueite is an extremely rare mineral from the osumilite group, found exclusively in meteorites, forming microscopic, blue grains.

## Characteristics Merrihueite is a very rare silicate from the osumilite group, occurring as small, rounded grains or aggregates typically not exceeding 1 mm in size. Its presence has only been confirmed in extraterrestrial matter – stony meteorites (chondrites). Due to the microscopic size of its crystals, its visual characteristics are difficult to observe without specialized equipment. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is approximately 5-6, and its density is close to 2.86 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Merrihueite has a characteristic pale blue or greenish-blue color. No distinct color varieties or commercial forms are recognized. ## History and Name It was discovered in 1965 in the Mezö-Madaras meteorite, which fell in what is now Romania in 1852. The mineral is named in honor of Craig M. Merrihue (1933-1965), an American geochemist from the University of California, Berkeley, a pioneer in the field of noble gas analysis in meteorites, who died in an accident in the Alps. ## Applications Merrihueite has no industrial applications. Its significance is purely scientific and collectible, as a component of rare meteorite types.

Properties

Mohs hardness
5-6
Color
Greenish-blue
Luster
Vitreous
Streak
White
Density
0
Cleavage
Imperfect on {0001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of merrihueite is possible only through advanced laboratory methods, such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD), due to its microscopic size and occurrence within a complex matrix. Under a microscope, it is distinguished by its pale blue color and weak pleochroism. ## Distinguishing from Similar Minerals It can be confused with other blue minerals found in chondrites, such as roedderite, which has a very similar composition and properties. Definitive differentiation requires precise chemical analysis, particularly the iron to magnesium ratio. ## Crystal Forms It typically occurs as anhedral (irregularly shaped), rounded grains or small granular aggregates embedded in the meteorite matrix.

Geological environment

## Genesis Merrihueite is an extraterrestrial mineral. It forms as a result of metamorphic processes occurring within the parent asteroids from which chondrites originate. It forms under conditions of high temperature and low pressure, in a reduced (oxygen-poor) environment. ## Mineral Associations It most commonly co-occurs with minerals typical of chondrites, such as olivine, pyroxene (enstatite, diopside), plagioclase, as well as roedderite, yagiite, whitlockite, and metals (kamacite, taenite). ## Localities Its occurrence has been confirmed in several stony meteorites (chondrites). In addition to the type locality – the Mezö-Madaras meteorite (Romania) – it has been identified in meteorites such as Tieschitz (Czech Republic), Yamato 74370 (Antarctica), Dar al Gani 474 (Libya), and Dhofar 224 (Oman).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a merrihueite specimen is identical to the quality of the meteorite itself in which the mineral occurs. For collectors and researchers, the size and richness of merrihueite aggregates visible in a cut and polished meteorite slice are important. Due to the microscopic nature of the mineral, specimens are primarily evaluated based on their scientific value and the rarity of the meteorite itself. ## Popular Localities The most well-known source is the Mezö-Madaras meteorite, however, it is a historical fall and material from it is extremely rare. Specimens from other confirmed localities, such as the Atacama Desert or Antarctica, are almost exclusively available in scientific institutions and specialized collections.

Care and storage

## Cleaning Specimens (meteorites) containing merrihueite should generally not be wet-cleaned. Dust can be removed very carefully using a soft brush or a photographic air blower. ## What to Avoid Avoid contact with water, chemicals, acids, and cleaning agents, which can damage both the mineral itself and the surrounding meteorite matrix. Protect it from moisture, which can cause corrosion of metallic phases in the meteorite. ## Storage Store in stable, dry conditions, preferably in an airtight container (e.g., a membrane box) with a desiccant (silica gel). Protect from dust and mechanical damage.

External references

Sources

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