Chromphyllite

Chemical formula: KCr₃+₂(Si₃Al)O₁₀(OH)₂

Chromophyllite is a rare, green mica group mineral, being the chromium analog of muscovite, found in metamorphic rocks.

## Characteristics Chromophyllite is a mineral from the mica group, belonging to the phyllosilicates. It is the chromium (Cr³⁺) analog of muscovite. It forms flakes, scales, and scaly aggregates, rarely forming distinct, tabular crystals with a pseudohexagonal outline. Its characteristic feature is an intense, emerald-green to dark-green color, resulting from its high chromium content. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 2.5, which is typical for micas. It has perfect, unidirectional cleavage, allowing for easy separation of thin, flexible flakes. Its luster is vitreous, and on cleavage planes, it can be pearly. It is translucent to opaque in thicker fragments. ## Colors and Varieties Chromophyllite occurs in shades from emerald-green to dark-green. Its color is so characteristic that it serves as a key diagnostic feature. No named varieties are distinguished, and the intensity of the color depends on the chromium content. ## History and Name The mineral's name, given in 1998 by Werner Schreyer, Klaus-Martin Gebert, Thomas Armbruster, and Christian Schmitz, comes from two Greek words: *chroma* (χρώμα) meaning "color" and *phyllon* (φύλλον) meaning "leaf". The name refers to its intense green color and its flaky, leafy structure, typical of micas. It was approved by the IMA as a new mineral in 1997 (IMA1997-013). The type locality is the Saranovskaya (Saranovskii) iron ore mine in the Urals, Russia. ## Applications Due to its extreme rarity, chromophyllite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and scientists studying chromium parageneses.

Properties

Mohs hardness: 2.5
Luster: Vitreous, Pearly
Streak: Light green
Density: 3.06
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Chromophyllite is primarily identified by its intense, emerald-green color, perfect unidirectional cleavage typical of micas, and its occurrence in the form of flakes and scales. Its characteristic co-occurrence with other chromium minerals in specific metamorphic rocks is also diagnostic. ## Distinguishing from Similar Minerals Chromophyllite can be confused with other green micas, mainly fuchsite (a chromium variety of muscovite) and chromceladonite. Distinguishing it from fuchsite is particularly difficult and often requires advanced chemical analyses (EDS, WDS), as fuchsite has a significantly lower chromium content. Chromceladonite has a similar composition but differs in structural details and elemental proportions. Its intensely green color distinguishes it from common muscovite. ## Crystal Forms Chromophyllite crystals are rare, usually appearing as small, tabular crystals with a pseudohexagonal outline. Most often, it occurs as scaly, flaky, or rosette-like aggregates, embedded in the host rock.

Geological environment

## Genesis Chromophyllite is a mineral of metamorphic origin. It forms under low-grade metamorphic conditions (greenschist facies) in rocks rich in potassium and chromium, and poor in aluminum. Its formation is associated with hydrothermal or metamorphic alteration of ultramafic rocks (e.g., chromitites) or within quartzites containing chromium minerals. ## Mineral Associations This mineral co-occurs with other chromium minerals and silicates. In the type locality (Saranovskaya, Russia), it was found in association with quartz, eskolaite, chromite, uvarovite, chromceladonite, pyrite, and rutile. In other localities, it may occur with fuchsite and other micas. ## Localities The most important and type locality for chromophyllite is the Saranovskaya (Saranovskii) chromite and iron ore mine in the Northern Urals, Russia. This is the only locality from which well-characterized specimens of this mineral originate, making it extremely rare on a global scale.

Rarity

Very rare

For collectors

## Quality Criteria The most prized chromophyllite specimens are those that contain rich aggregations of flakes with an intense, emerald-green color, contrasting with a light host rock (most often quartz). Rare, well-formed, pseudohexagonal crystals are exceptionally sought after. The size of the aggregates and the purity of the color significantly increase the collector's value of a specimen. ## Popular Localities The only source of collector specimens is the Saranovskaya mine in the Urals, Russia. Material from this locality is considered exemplary for this species, and practically all specimens available on the market come from there.

Care and storage

## Cleaning Chromophyllite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its low hardness and perfect cleavage, mechanical washing and ultrasonics should be avoided. If liquid is necessary, distilled water is recommended, followed by gentle drying without rubbing. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the mineral's structure. Chromophyllite flakes are flexible but easily permanently bent or broken, so any mechanical pressure should be avoided. Do not heat the specimen or expose it to sudden temperature changes. ## Storage Chromophyllite specimens are best stored in individual, padded collector boxes to protect them from scratching and mechanical damage. They should be protected from dust, which can accumulate between the flakes and be difficult to remove.

Sources

IMA Mineral List (CNMNC)