Erlianite

Chemical formula: Fe<sup>2+</sup><sub>4</sub>Fe<sup>3+</sup><sub>2</sub>Si<sub>6</sub>O<sub>15</sub>(OH)<sub>8</sub>

Erlianite is a very rare, black iron silicate mineral, forming fine, scaly aggregates in metamorphosed iron formations.

## Characteristics Erlianite is a black mineral with a metallic to submetallic luster. It occurs as very fine, scaly or platy crystals that form compact, earthy, or scaly aggregates. Due to the small size of the crystals, individual flakes are rarely visible to the naked eye. It is an opaque mineral. ## Physical Properties The luster of erlianite is described as metallic to submetallic. Its calculated density is approximately 3.45 g/cm³. The Mohs hardness has not yet been precisely determined. The mineral exhibits perfect cleavage in one plane, which is related to its platy structure. ## Colors and Varieties This mineral is monochromatic and occurs exclusively in black. No color or commercial varieties are known. ## History and Name Erlianite was recognized as a new mineral species by the International Mineralogical Association (IMA) in 1984. Its name comes from its discovery locality – the Erlian deposit, located in the Inner Mongolia Autonomous Region in China. ## Uses Erlianite has no industrial applications. Its significance is purely scientific and as a collector's item, being a very rare mineral species.

Properties

Luster
Metallic to Sub-Metallic
Streak
Black
Density
3.45
Cleavage
Perfect on {001}
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of erlianite include its black color, metallic luster, and occurrence as fine-scaly, compact aggregates. Key for identification is its specific occurrence environment – metamorphosed iron formations – and associated minerals. ## Distinguishing from Similar Minerals Erlianite can be confused with other black, platy minerals such as stilpnomelane, hematite, or graphite. It is distinguished from stilpnomelane by its geological context and harder associated minerals. Graphite is much softer and leaves a mark on paper. Final and certain identification is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Erlianite does not form well-developed, macroscopic crystals. It occurs as very fine, scaly or platy crystals gathered into dense, felted or earthy aggregates.

Geological environment

## Genesis Erlianite is a mineral of metamorphic origin. It forms under conditions of low-grade metamorphism acting on iron-rich sediments, known as banded iron formations (BIF). ## Mineral Associations This mineral occurs in association with other minerals typical of iron-rich rocks, such as magnetite, quartz, grunerite, stilpnomelane, and minnesotaite. ## Localities The only confirmed locality of erlianite in the world is its type locality – the Erlian deposit in Sonid Zuoqi (Inner Mongolia, China).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of erlianite specimens, being a typical "micromineral," is assessed based on the richness and extent of the aggregate on the host rock. Samples where black erlianite clusters create a clear contrast with other associated minerals, such as quartz, are most valued. Due to its rarity, every authentic specimen holds significant scientific value. ## Popular Localities The only source of erlianite specimens is its type locality in China. Material from this location is extremely difficult to obtain and rarely appears on the collector's market.

Care and storage

## Cleaning Erlianite specimens are typically very delicate. For dust removal, it is best to use canned compressed air or a small photographic blower. Wet cleaning, especially with detergents, should be avoided as they could penetrate the porous structure of the aggregates. ## What to Avoid Avoid contact with chemicals, acids, and bases. The mineral's structure is susceptible to mechanical damage, so it should be protected from impacts, scratching, and vibrations. Ultrasonic cleaners should not be used. ## Storage It is recommended to store specimens in closed, padded "micromount" boxes, which protect them from dust, light, and physical damage. Each specimen should be properly labeled, taking into account its fragility.

Sources

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