Ekplexite

Chemical formula: (Nb<sup>5+</sup>,Mo)S<sub>2</sub>·(Mg<sub>1-x</sub>Al<sub>x</sub>)(OH)<sub>2+x</sub>

Ekplexite is an extremely rare, layered niobium and molybdenum sulfide, occurring as hexagonal platelets in serpentinites.

## Characteristics Ekplexite is a mineral with a metallic luster and lead-gray color, forming very small, hexagonal crystals in the form of platelets or flakes. Its maximum observed size is only 0.2 mm. It typically occurs as inclusions in other minerals, mainly in lizardite, a variety of serpentine. ## Physical Properties Due to the extremely small size of its crystals, most of ekplexite's physical properties have not been precisely determined. Hardness and density are unknown. The mineral exhibits perfect cleavage in one direction, which is typical for its layered crystal structure. It has a metallic luster and is opaque. ## Colors and Varieties This mineral is lead-gray with a metallic luster. No color varieties or commercial varieties are known. ## History and Name Ekplexite was discovered and described in 2007 by N.V. Chukanov and co-workers. Its name comes from the Greek word *έκπληξη* (ekplexi), meaning "surprise" or "astonishment," referring to its unexpected chemical composition and structure, which is a combination of sulfide and hydroxide layers. ## Uses Ekplexite has no industrial application and is solely an object of scientific and collecting interest for specialists accumulating type minerals (from the type locality) or microminerals.

Properties

Luster
Metallic
Streak
Black
Cleavage
Perfect on {0001}
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identification of ekplexite is possible only through advanced analytical methods, such as electron spectroscopy (EDS/WDS) combined with X-ray diffraction (XRD), due to its extremely small size and occurrence as inclusions. Visually, under high magnification, small, hexagonal, metallic flakes can be observed. ## Distinguishing from Similar Minerals It can be confused with other fine-grained sulfides of similar appearance, such as molybdenite or graphite, which also form hexagonal flakes with a metallic luster. Differentiation requires chemical analysis – the presence of niobium, molybdenum, magnesium, and aluminum is characteristic of ekplexite. ## Crystal Forms Ekplexite forms thin, hexagonal crystals in the form of platelets and flakes, with a maximum diameter of up to 0.2 mm and a thickness of up to 0.01 mm.

Geological environment

## Genesis Ekplexite forms as a result of hydrothermal or metamorphic processes within serpentinized ultramafic rocks (serpentinites). It is a secondary mineral, crystallizing at low temperatures. ## Mineral Associations This mineral occurs in paragenesis with lizardite (a variety of serpentine), magnesite, chromite, coomite, native nickel, awaruite, heazlewoodite, and other nickel sulfides. ## Localities The only confirmed locality of ekplexite in the world (type locality) is the chromite deposit in the Uktus massif, located on the outskirts of Yekaterinburg in the Middle Urals, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an ekplexite specimen is primarily assessed based on the confirmation of its identity by analytical methods. From a collector's perspective, the most desirable specimens are those where ekplexite crystals, although microscopic, are as well-formed, visible, and distinct from the surrounding mineral matrix (lizardite) as possible. Every specimen from the type locality is valuable due to the extreme rarity of the mineral. ## Popular Localities The only source of specimens is the type locality – the Uktus massif in the Urals, Russia. Collector material is virtually non-existent on the commercial market and is mainly found in institutional and specialized collections.

Care and storage

## Cleaning Specimens containing ekplexite, which are typically microminerals, should not be cleaned mechanically or chemically. Any attempts at cleaning may damage or dislodge the tiny crystals. If dust removal is necessary, a gentle stream of compressed air can be used from a safe distance. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. Do not expose specimens to ultrasound. Due to its nature (sulfide), it should be protected from moisture and conditions conducive to oxidation. ## Storage Micromineralogical specimens of ekplexite are best stored in specialized, sealed "micromount" boxes, which protect them from dust, moisture, and mechanical damage.

External references

Sources

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