Ferroaluminoceladonite

Chemical formula: KFe²⁺AlSi₄O₁₀(OH)₂

Ferroaluminoceladonite is a rare, green or white mica group mineral, being the aluminum and ferrous iron analogue of celadonite.

## Characteristics Ferroaluminoceladonite is a mica group mineral belonging to the celadonite subgroup. It forms very fine, scaly crystals, which usually occur as compact, earthy, or massive aggregates. Its appearance is inconspicuous, and the aggregates have a dull, earthy luster. Due to the microscopic size of the crystals, the visual characteristics of individual specimens are difficult to assess with the naked eye. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2 to 2.5, meaning it can be scratched with a fingernail. It is translucent. The luster is typically earthy, dull. ## Colors and Varieties Ferroaluminoceladonite occurs in a characteristic, pale, celadon-green color, from which the name of the entire celadonite group is derived. White specimens are also found. No commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – indicating the dominance of iron (Ferro) and aluminum (alumino) and its relationship to the previously known celadonite. It was formally described and recognized as a new mineral in 1997. The type locality (the place of its first discovery and description) is the Hokonui Hills in the Southland region of New Zealand. ## Uses Ferroaluminoceladonite has no industrial applications. Its significance is purely scientific and collectible, as a rare member of the mica group.

Properties

Mohs hardness
2-2.5
Luster
Earthy
Streak
White, Pale grey
Density
0
Cleavage
(001)
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying ferroaluminoceladonite in the field is practically impossible without advanced analysis. Its characteristic features include very low hardness (2-2.5), celadon-green or white color, earthy, dull aggregates, and co-occurrence with other minerals in volcanic rocks. Identification requires chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Ferroaluminoceladonite is visually indistinguishable from celadonite, glauconite, and other similar green clay minerals. All of them form similar earthy coatings and fillings. Definitive differentiation is only possible based on detailed chemical composition analysis, which will show the appropriate proportions of iron, aluminum, magnesium, and potassium. ## Crystal Forms This mineral forms microscopic, platy or scaly crystals. It occurs as very fine-grained, massive, and earthy aggregates, often as fillings in gas vesicles or veins in host rocks.

Geological environment

## Genesis Ferroaluminoceladonite is a secondary mineral, formed as a result of low-temperature hydrothermal processes or metasomatism. It typically forms as an alteration product of primary minerals (such as pyroxenes, amphiboles, or biotite) in volcanic rocks, e.g., andesites, basalts, and tuffs. It fills gas vesicles and fractures in these rocks. ## Mineral Associations This mineral often co-occurs with other secondary minerals, such as quartz (chalcedony, agate), calcite, heulandite, laumontite, and other zeolites. At the type locality in New Zealand, it was found in association with quartz, laumontite, and prehnite. ## Localities The most important and best-documented locality is its type locality – the Hokonui Hills in New Zealand. It is a very rare mineral and known from only a few places worldwide. Confirmed occurrences are scarce and primarily of scientific importance.

Rarity

Very rare

For collectors

## Quality Criteria The quality of ferroaluminoceladonite specimens is assessed primarily based on the abundance of its occurrence on the rock matrix and the intensity and purity of its color. As it is a rare mineral, any specimen from a well-documented locality, with analytically confirmed identity, is valuable to specialized collectors of rare minerals and micromounts. ## Popular Localities The only significant collecting locality is the type locality in the Hokonui Hills, New Zealand. Specimens from this location are the most sought after.

Care and storage

## Cleaning Ferroaluminoceladonite specimens are very soft and fragile. They should be cleaned only with a soft brush, dry, to remove dust. Using water, especially under pressure, can damage the delicate, earthy aggregates. ## What to Avoid Avoid contact with water, chemicals, acids, and detergents. The mineral is susceptible to scratching and abrasion, so it must be protected from contact with harder minerals. It should not be heated or exposed to prolonged moisture. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust, mechanical damage, and moisture. This is not a mineral suitable for display in open showcases without adequate protection.

External references

Sources

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