Ferroindialite
Chemical formula: (Fe<sup>2+</sup>,Mg)<sub>2</sub>Al<sub>3</sub>(AlSi<sub>5</sub>)O<sub>18</sub>
Ferroindialite is an extremely rare cyclosilicate mineral, an iron-rich analog of cordierite and indialite.
Properties
- Mohs hardness
- 7-7.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.76
- Cleavage
- Distinct on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identification of ferroindialite is impossible without advanced laboratory techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the dominance of iron over magnesium, and structural analysis (e.g., X-ray diffraction - XRD) to determine the hexagonal symmetry of the crystals. Visual identification in the field or in a collection is unfeasible. ## Distinguishing from Similar Minerals Ferroindialite is visually indistinguishable from indialite, cordierite, and sekaninaite. All these minerals form isomorphic series, and their differentiation is based solely on precise determination of chemical composition (ratio of Mg, Fe²⁺, Mn) and, in the case of cordierite, crystallographic system (orthorhombic vs. hexagonal indialite). ## Crystal Forms This mineral forms very small, hexagonal, tabular or prismatic crystals. It also occurs as irregular grains embedded in other minerals of the host rock.
Geological environment
## Genesis Ferroindialite forms under conditions of high-grade contact metamorphism (sanidinite facies) or pyrometamorphism. It forms at extremely high temperatures (above 800°C) and low pressure. It is a product of the alteration of iron-rich and aluminosilicate sediments or clay rocks that have undergone melting and recrystallization in contact with a magmatic intrusion or as a result of the burning of underground coal seams (paralavas). ## Mineral Associations This mineral coexists with other high-temperature minerals such as tridymite, cristobalite, mullite, hematite, magnetite, hercynite, fayalite, sanidine, and silica glass. ## Localities The most important and well-documented localities worldwide include: - Bokaro coalfields in Jharkhand, India (type locality) - product of burnt coal shales. - Schicklersspitze in the Ötztal Alps, Tyrol, Austria - in metamorphic xenoliths. - Mount Carmel in Israel - in pyrometamorphic rocks of the Hatrurim Complex.
Rarity
Extremely rare
For collectors
## Quality Criteria From a collector's perspective, the only criterion for evaluation is the scientific significance of the specimen. Since ferroindialite occurs as microscopic crystals, their aesthetics, color, or transparency are irrelevant. The value of a specimen lies in its confirmed authenticity (supported by analysis), the abundance of its occurrence on the matrix, and its association with rare accompanying minerals. Specimens from the type locality (Bokaro) or other classic localities are most sought after by specialized micromount collectors. ## Market Prices The market for this mineral is very limited and niche. Prices for analyzed microspecimens can range from tens to several hundred dollars, depending on the scientific quality and origin of the material.
Care and storage
## Cleaning Ferroindialite specimens, due to their microscopic size and embedding in the host rock, do not require and should not be subjected to cleaning. Any attempt at mechanical or chemical intervention risks irreversible damage or destruction of the material. ## What to Avoid All forms of cleaning should be avoided, including ultrasonics, chemical agents, and even water. Specimens should be protected from abrasion, impacts, and extreme temperature changes. ## Storage Storage should take place under stable conditions, preferably in a specialized "micromount" box, which protects the delicate material from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided.