Chromceladonite

Chemical formula: KMgCr<sup>3+</sup>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>

Chromceladonite is a rare, green mica group mineral, a chromium analog of celadonite, found in metamorphic rocks.

## Characteristics Chromceladonite is a mineral from the mica group, belonging to the layered silicates. It forms very fine, scaly crystals, which usually occur as dense, felted aggregates or as coatings and crusts on other minerals. Its characteristic feature is an intense, emerald-green to dark-green color, resulting from the presence of chromium in its chemical structure. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 2. It is light, with a density close to 3 g/cm³. The crystals exhibit perfect cleavage in one direction, typical of mica group minerals, which causes them to easily separate into thin, flexible flakes. The luster is dull to silky in aggregates. ## Colors and Varieties Chromceladonite occurs in shades of green, from emerald to dark green and greenish-black. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of chromium (Latin: *chromium*) and its structural similarity to celadonite. It was first described by A.I. Chashchukhin, V.V. Zaykov, and E.V. Vlasova in 1995 after being found in a chromium ore deposit in Russia. ## Uses Due to its rarity and occurrence in microscopic aggregates, chromceladonite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
2
Luster
Dull
Streak
Light green
Density
2.96
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Chromceladonite can be identified by its characteristic, intensely green color, very low hardness (it can be scratched with a fingernail), and occurrence in the form of fine-scaly, felted aggregates or coatings. Its green streak is also a diagnostic feature. ## Distinguishing from Similar Minerals It can be confused with other green micas, such as fuchsite, celadonite, or glauconite. Distinguishing it from celadonite and glauconite requires advanced chemical analysis to confirm the dominance of chromium. Fuchsite (a variety of muscovite) is usually harder (2-2.5) and often exhibits a more silvery or pearly luster. Other green secondary minerals, like malachite, react with acid, which chromceladonite does not. ## Crystal Forms It forms microscopic, pseudohexagonal crystals with a platy or scaly habit. Most often, it occurs as compact, earthy, or felted masses, as well as thin coatings and crusts.

Geological environment

## Genesis Chromceladonite is a low-temperature hydrothermal mineral. It forms as a result of metasomatic alteration of ultramafic rocks (e.g., serpentinites) or in hydrothermal zones associated with copper and zinc sulfide deposits (VMS type) and chromium ores. Its presence is strongly linked to a chromium-rich environment. ## Mineral Associations It often co-occurs with minerals such as: quartz, calcite, dolomite, pyrite, chalcopyrite, sphalerite, hematite, magnetite, chromite, as well as other micas (fuchsite) and serpentine group minerals. ## Localities The most important localities worldwide include the Aganozerskoye chromium ore deposit in the Polar Urals, Russia (type locality), the Isokangas sulfide deposit in Finland, and the Dzhusa deposit in the southern Urals, Russia.

Rarity

Rare

For collectors

## Quality Criteria The collector's appeal of a specimen primarily depends on the intensity and saturation of its green color. The most prized specimens are those where chromceladonite forms distinct, rich coatings or fillings of a vibrant, emerald color, contrasting with a light matrix rock (e.g., quartz or calcite). The size of the specimen and the abundance of the mineral on the matrix also significantly increase its value. ## Popular Localities Specimens from the Finnish Isokangas deposit and the Russian Dzhusa deposit in the Urals are the most well-known on the collector's market and are valued for their intense color.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its softness and possible reactivity, contact with water and any chemical agents should be avoided. ## What to Avoid Avoid washing in water, ultrasonic cleaning, and the use of any acids or detergents. The mineral is very soft and can be easily scratched or mechanically damaged. It should be protected from high temperatures. ## Storage Chromceladonite specimens should be stored in closed, dry containers or display boxes to protect them from dust and mechanical damage. It is best to keep them away from harder minerals that could scratch them.

Sources

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