Ferrokinoshitalite

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

Ferrokinoshitalite is a rare mica group mineral, brittle, with a dark brown to black color and a vitreous luster.

## Characteristics Ferrokinoshitalite is a mineral from the mica group, belonging to the phyllosilicates. It forms small, tabular or platy crystals, often aggregated into rosettes or scaly masses. Its color is typically dark brown to almost black. It is a brittle mineral, and its thin lamellae exhibit some flexibility. ## Physical Properties This mineral is characterized by a hardness of approximately 2.5 on the Mohs scale, meaning it is relatively soft. It has a vitreous luster, and a slightly pearly luster on fracture surfaces. It is translucent to opaque, especially in thicker fragments. Its density is approximately 3.33 g/cm³. ## Colors and Varieties Dark brown, brownish-black, and black colors dominate. No distinct color varieties or commercial varieties have been identified. ## History and Name The name "ferrokinoshitalite" refers to its chemical composition – a high iron content (ferro) – and its structural relationship to kinoshitalite. It was first described by M. Z. Gugu and others in 1999 after examining material from the Shizhuyuan mine in Hunan Province, China. The mineral was approved by the International Mineralogical Association (IMA) in 1998. ## Uses Ferrokinoshitalite has no industrial applications. Its significance is purely scientific and as a collector's item.

Properties

Mohs hardness
2.5
Luster
Vitreous, Pearly
Streak
Pale brown
Density
3.33
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Ferrokinoshitalite can be identified by its dark brown to black color, platy or scaly form, and perfect cleavage in one direction, typical of micas. Its vitreous luster and occurrence in association with other skarn minerals are also characteristic. ## Distinguishing from Similar Minerals It can be confused with other dark micas, such as biotite or phlogopite. Distinguishing it from biotite often requires chemical analysis to confirm the dominance of barium over potassium. Compared to phlogopite, ferrokinoshitalite is usually significantly darker due to its high iron content. ## Crystal Forms Crystals are most often tabular, with a pseudohexagonal outline. It usually forms scaly, platy aggregates, as well as small, rosette-like clusters.

Geological environment

## Genesis Ferrokinoshitalite is a mineral formed in contact zones, in magnesian skarns. It forms as a result of metasomatic processes at high temperatures, at the contact of granitic intrusions with carbonate rocks, such as dolomites. ## Mineral Associations It most commonly co-occurs with minerals such as diopside, phlogopite, chondrodite, calcite, dolomite, as well as ore minerals, e.g., pyrite and magnetite. ## Localities The most important and type locality for this mineral is the Shizhuyuan tungsten and tin mine in the Chenzhou autonomous region, Hunan Province, China. This is, to date, the only confirmed and well-documented locality for this mineral in the world.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, specimens with well-formed, sharp crystals with a distinct pseudohexagonal outline are most valuable. Rich aggregates and rosettes on a contrasting matrix, for example, on white calcite or dolomite, are also prized. Luster and absence of mechanical damage significantly increase the value of a specimen. ## Popular Localities All collector's specimens originate from a single location – the Shizhuyuan mine in China. This is the only source of material available on the market.

Care and storage

## Cleaning Ferrokinoshitalite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its softness and platy structure, ultrasonic cleaners and strong jets of water should be avoided. If water is necessary, it should be distilled water. ## What to Avoid Contact with acids and other chemicals that may react with the mineral should be avoided. It is susceptible to mechanical damage, such as scratches, impacts, or bending of the lamellae. It should not be heated or exposed to sudden temperature changes. ## Storage Collector's specimens of ferrokinoshitalite are best stored in separate, padded boxes to protect them from scratching and damage to delicate crystals. Areas with high humidity and direct exposure to sunlight should be avoided.

Sources

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