Indigirite

Chemical formula: Mg<sub>2</sub>Al<sub>2</sub>(CO<sub>3</sub>)<sub>4</sub>(OH)<sub>2</sub>·15H<sub>2</sub>O

Indigirite is a very rare, hydrated magnesium and aluminum carbonate, occurring as soft, earthy or fibrous aggregates.

## Characteristics Indigirite is a mineral from the carbonate group, chemically a hydrated magnesium and aluminum carbonate. It occurs almost exclusively in the form of very fine-grained, soft, and brittle aggregates resembling chalk or clay. Less commonly, it forms fibrous aggregates or small spherulites (spherical aggregates). Due to the microscopic size of its crystals, its visual features are inconspicuous, and specimens most often appear as white, earthy coatings and masses. ## Physical Properties This mineral is exceptionally soft, with a Mohs hardness of about 2, meaning it can be scratched with a fingernail. It has a low density, ranging from 1.85 to 1.9 g/cm³. The luster on fracture surfaces can be pearly, but in the case of earthy aggregates, it is dull. Thin fragments of the mineral may be translucent, but its aggregates are completely opaque. ## Colors and Varieties Indigirite is usually white. It can take on yellowish or grayish hues, which is a result of admixtures or impurities. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from the Indigirka River in Yakutia (Russia), near which it was first found. Indigirite was described as a new mineral species in 1966 by a team of Russian researchers (K.N. Nikiforov et al.) based on samples from the Borie-Uriakh gold and antimony deposit. ## Uses Due to its extreme rarity and inconspicuous appearance, indigirite has no industrial application. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Mohs hardness
2
Luster
Pearly, Dull, Earthy
Streak
White
Density
1.85-1.9
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of indigirite include its chalky white color, earthy or fibrous habit, very low hardness (approx. 2 on the Mohs scale), and low density. It reacts vigorously with hydrochloric acid, which is typical for carbonates. A key diagnostic clue is its specific occurrence environment – oxidation zones in permafrost areas. ## Distinguishing from Similar Minerals Indigirite can be easily confused with other white, secondary carbonate minerals of similar hardness and appearance, such as hydromagnesite or artinite. It can also resemble some clay minerals, e.g., kaolinite. Reliable differentiation of these minerals under amateur conditions is practically impossible and usually requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Indigirite forms almost exclusively microcrystalline aggregates: earthy, chalk-like, or powdery masses. Less commonly, it is observed as fibrous aggregates or small spherulites. Well-formed crystals visible to the naked eye are not known.

Geological environment

## Genesis Indigirite is a secondary mineral, formed under specific climatic conditions. It forms in the oxidation zones of ore deposits (mainly gold and antimony) located within serpentinite rocks in permafrost areas. It results from the weathering and alteration of earlier minerals at low temperatures. ## Mineral Associations This mineral occurs in association with other secondary magnesium carbonates and hydroxides. It most commonly co-occurs with minerals from the serpentine group, hydromagnesite, artinite, pyroaurite, manasseite, brucite, as well as dolomite and calcite. ## Localities Indigirite is an extremely rare mineral. The main and typical locality for its occurrence is the Borie-Uriakh (Börö-Uryakh) gold and antimony deposit on the Indigirka River in Yakutia, Russia. This is practically the only locality from which well-documented specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The quality of indigirite specimens is assessed primarily based on the richness and purity of the aggregate on the matrix, rather than aesthetic values. Since it is a mineral mainly for systematic collectors, samples with well-identified associations of other rare minerals and with precisely determined localities (preferably from the type locality) are most desirable. The size of the specimen is less important than its representativeness. ## Popular Localities The only known and valued source of collectible indigirite specimens is its type locality – the Borie-Uriakh deposit in Yakutia (Russia). Specimens from this location are the standard for this mineral in collections worldwide.

Care and storage

## Cleaning Indigirite specimens are extremely delicate, soft, and brittle. They should only be dry cleaned, using a very soft brush to remove dust. Blowing dust with compressed air from a distance is also permissible. Contact with water or other liquids is not recommended, as it can damage or dissolve the mineral. ## What to Avoid Contact with acids, in which indigirite rapidly dissolves, should be strictly avoided. The mineral is sensitive to elevated temperatures, which can cause dehydration and destruction of its structure. It should be protected from moisture, all chemicals, and mechanical damage. ## Storage It is recommended to store specimens in closed, padded "micromount" boxes to protect them from physical damage, dust, and humidity changes. Display should be in stable conditions, away from heat sources and direct sunlight.

Sources

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