Clinoferrosilite

Chemical formula: Fe<sup>₂+</sup>SiO<sub>₃</sub>

Clinoferrosilite from the pyroxene group, a monoclinic polymorph of ferrosilite, found mainly in meteorites and metamorphic rocks.

## Characteristics Clinoferrosilite is a mineral from the pyroxene group, belonging to the inosilicates. It is a monoclinic, high-temperature polymorphic variety of ferrosilite (FeSiO₃). It usually occurs in granular or fibrous aggregates, and well-formed crystals are rare. Its appearance is inconspicuous, most often having dark, muted colors. ## Physical Properties Clinoferrosilite is characterized by a hardness ranging from 5-6 on the Mohs scale. It has a vitreous luster and is a relatively dense mineral, which results from its high iron content. It is brittle, and its crystals exhibit good cleavage in two directions, typical for pyroxenes. ## Colors and Varieties This mineral takes on colors from greenish, through brownish-green, to almost black. Its color is directly related to its high iron content. No named color or commercial varieties are distinguished. ## History and Name The name "clinoferrosilite" refers to its monoclinic crystallography and chemical composition – high content of iron (*ferro*) and silicon (*silite*). It was described as a distinct mineral in 1935. It is recognized by the International Mineralogical Association (IMA). ## Applications Clinoferrosilite has no industrial application. Its significance is purely scientific, as an indicator of conditions prevailing during rock formation, and as a collector's item, although it is a mineral sought mainly by specialized collectors and scientific institutions.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Grayish green
Density: 3.89-3.96
Cleavage: Good on {210}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Clinoferrosilite is difficult to identify unequivocally by visual inspection. Key features include its dark, greenish-brown color, vitreous luster, and pyroxene-typical cleavage at an angle close to 90 degrees. It occurs in characteristic parageneses, often in iron-rich metamorphic rocks or in meteorites. ## Distinguishing from Similar Minerals It can be confused with other dark pyroxenes, such as hedenbergite or augite. Differentiation requires advanced research methods, such as chemical analysis (EDS/WDS) to confirm its composition (almost pure iron silicate) or X-ray diffraction (XRD) to determine its crystal structure. It differs from orthorhombic ferrosilite in its crystallographic system. ## Crystal Forms Well-formed crystals are rare and appear as short, thick prisms. Most often, it forms granular, fibrous, or radial aggregates within the rock mass.

Geological environment

## Genesis Clinoferrosilite is a mineral that forms under conditions of high temperature and relatively low pressure. It occurs in iron-rich metamorphic rocks, such as eulysites and metamorphosed iron formations. It is also found as a component of some igneous rocks and, importantly, in meteorites (both chondrites and achondrites, e.g., in ureilites), where it is a product of magma crystallization under reducing conditions. ## Mineral Associations In terrestrial rocks, it coexists with other iron-rich minerals such as fayalite (an olivine variety), hedenbergite, garnets (almandine), quartz, magnetite, and grunerite. In meteorites, it is accompanied by olivine, pigeonite, graphite, and diamond, among others. ## Localities Significant occurrences of clinoferrosilite in terrestrial rocks have been reported in Broken Hill, Australia; in the Skaergaard igneous complex, Greenland; in the Labrador region, Canada; and in the Gunflint iron formation in Minnesota, USA. It is also identified in many meteorites that have fallen to Earth.

Rarity

Rare

For collectors

## Quality Criteria The collector's appeal of clinoferrosilite is low for the average collector but high for specialized collectors and institutions. Most valued are specimens with well-formed, even if small, crystals with a visible prismatic habit. A well-documented locality is also important, especially if it is a classic site (a "type locality") or a rare one. Specimens of extraterrestrial origin (identified in meteorites) have particular scientific and collector value. ## Popular Localities For collectors specializing in rock-forming minerals, the most sought-after specimens come from classic localities such as the Skaergaard complex (Greenland) or Obsidian Cliff in Yellowstone National Park (USA). Valuable microminerals also come from Mt. Vesuvius in Italy.

Care and storage

## Cleaning Clinoferrosilite specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to potential reactivity with acids and the possibility of oxidation, contact with water and any chemical agents should be avoided. ## What to Avoid Ultrasonic cleaners should be avoided, as they can damage brittle crystals. The mineral is sensitive to acids. Prolonged exposure to humid air can lead to slow oxidation of iron and a change in the surface color to rusty brown. ## Storage It is recommended to store specimens in a dry place, preferably in closed display boxes or cabinets, to limit access to moisture and dust. Avoid storing with minerals that could scratch it (harder than 6 on the Mohs scale).

Sources

IMA Mineral List (CNMNC)