Ferri-katophorite
Chemical formula: Na(NaCa)(Mg₄Fe³⁺)(Si₇Al)O₂₂(OH)₂
A rare sodium amphibole from the katophorite group, distinguished by the presence of trivalent iron and its occurrence in metamorphic rocks.
Properties
- Mohs hardness
- 5-6
- Luster
- Vitreous
- Streak
- Greenish-gray
- Density
- 0
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Field identification of ferri-katophorite is practically impossible and requires specialized analytical methods, such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD). Its basic physical characteristics, such as color, habit, and hardness, are common to many other amphiboles. ## Distinguishing from Similar Minerals Ferri-katophorite is almost impossible to distinguish with the naked eye from other dark amphiboles, such as hornblende, arfvedsonite, riebeckite, or other minerals from the katophorite group (magnesio-katophorite). Certain differentiation is possible only based on chemical composition analysis. ## Crystal Forms This mineral forms columnar or prismatic crystals, often acicular or fibrous in habit. It occurs as granular, radial, or tangled fibrous aggregates.
Geological environment
## Genesis Ferri-katophorite is a characteristic mineral of metamorphic rocks that have undergone transformations under conditions of high pressure and relatively low temperature. It primarily forms in glaucophane schists and in rocks rich in sodium and iron. ## Mineral Associations It most commonly co-occurs with minerals such as glaucophane, crossite, albite, epidote, quartz, chlorite, and other sodium amphiboles. ## Localities The most important and best-documented occurrences of ferri-katophorite are found on Sesili Island (Sesilia) in Greece, which is its type locality. It is also known from the Biga Peninsula in Turkey and from several other rare localities worldwide with similar geological environments.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of ferri-katophorite is limited due to its rarity and identification difficulties. The most desirable specimens are those with well-formed, visible prismatic crystals, contrasting with a light matrix rock (e.g., with quartz). Specimens from the type locality (Sesili, Greece) have the highest scientific and collector value. ## Popular Localities The only source of specimens of collector significance is its type locality in Greece.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or a paintbrush to remove dust. For heavier dirt, compressed air can be used. Avoid contact with water, especially for specimens with a fibrous structure. ## What to Avoid Absolutely avoid all chemical agents, acids, and detergents, which can react with the mineral and damage its surface. Ferri-katophorite is sensitive to rapid temperature changes. It should not be exposed to prolonged direct sunlight. ## Storage Collector's specimens of ferri-katophorite, especially those with a delicate, fibrous structure, should be stored in closed display boxes to protect them from dust and mechanical damage. Avoid storage in humid environments.