Ferromerrillite

Chemical formula: Ca₉NaFe₂+(PO₄)₇

Ferromerrillite is an extremely rare phosphate from the merrillite group, found exclusively in meteorites, distinguished by the presence of iron.

## Characteristics Ferromerrillite is a mineral belonging to the merrillite group, occurring as microscopic, anhedral (not exhibiting its own crystallographic form) grains. It is typically colorless and has a vitreous luster. Due to its extreme rarity and occurrence only in meteorites, observation of well-formed specimens is impossible. This mineral is important for scientists studying the composition and history of extraterrestrial bodies. ## Physical Properties Due to the microscopic size of the grains, most physical properties, such as hardness, density, or fracture, have not been precisely determined. The mineral is transparent and exhibits a vitreous luster. No cleavage has been observed. ## Colors and Varieties Ferromerrillite is usually colorless. No colored varieties are known. ## History and Name The name "ferromerrillite" refers to its chemical composition – the dominance of iron (ferro) and its relation to the associated mineral, merrillite. It was officially recognized by the International Mineralogical Association (IMA) in 2006. The mineral was identified in meteorites found in various parts of the world, including the Suizhou meteorite, which fell in China. ## Uses Ferromerrillite has no commercial or industrial applications. Its significance is purely scientific, serving as an indicator of processes occurring in the parent bodies of meteorites.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 3.12
Cleavage: None
Fracture: Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of ferromerrillite is impossible without advanced analytical techniques. This requires the use of an electron microprobe (for chemical composition analysis) and X-ray diffraction (for determining crystal structure). It occurs as microscopic, colorless grains embedded in the meteorite matrix. ## Distinguishing from Similar Minerals Microscopically, it is almost identical to other minerals from the merrillite group, such as merrillite, whitlockite, or brianite. Differentiation is based solely on precise chemical analysis, which shows the dominance of iron (Fe²⁺) over magnesium (Mg) in a specific position within the crystal structure. ## Crystal Forms Ferromerrillite forms exclusively anhedral, irregular grains with sizes not exceeding several hundred micrometers.

Geological environment

## Genesis Ferromerrillite is a mineral of extraterrestrial origin. It crystallizes under conditions of very low oxygen fugacity and absence of water, as prevailed within the parent bodies of some meteorites (e.g., asteroids). It forms as a result of metamorphic processes or crystallization from magma in a phosphorus-rich environment. ## Mineral Associations It co-occurs with other minerals typical of meteorites, such as olivine, pyroxene, plagioclase, troilite, kamacite, taenite, and other phosphates, e.g., apatite and brianite. ## Locations Its occurrence has been confirmed exclusively in meteorites. It has been identified, among others, in chondrites (e.g., Suizhou, Zag, Sahara 98222) and in mesosiderites (e.g., Vaca Muerta). These are the only known localities for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria Ferromerrillite is not a collector's mineral in the traditional sense. It does not form aesthetic specimens. Its value is purely scientific and contextual – it depends on the significance of the meteorite in which it was found. Meteorite collectors may value specimens in which the presence of this rare mineral has been confirmed, but its presence does not affect the external appearance of the specimen.

Care and storage

## Cleaning Specimens containing ferromerrillite (meteorites) are extremely valuable and sensitive. Cleaning should be kept to an absolute minimum and performed only by specialists in laboratory conditions, typically using compressed air or very gentle, dry methods. ## What to Avoid Contact with water, chemicals, as well as sudden changes in temperature and humidity should be avoided. Meteorites containing ferromerrillite may contain minerals sensitive to oxidation and corrosion. ## Storage Storage requires stable conditions. It is best to keep specimens in sealed containers with a desiccant (e.g., silica gel), in a dark and cool place. Display should take place in a controlled environment.

Sources

IMA Mineral List (CNMNC)