Potassic-ferro-ferri-taramite

Chemical formula: K(NaCa)(Fe₂+₃Fe₃+₂)(Si₆Al₂)O₂₂(OH)₂

Potassic-ferro-ferri-taramite is a rare sodium-calcium amphibole, distinguished by its complex chemical composition with a dominance of potassium and iron.

## Characteristics Potassic-ferro-ferri-taramite is a complex silicate from the amphibole group, belonging to the sodic-calcic amphibole subgroup. This mineral forms prismatic, columnar crystals, often occurring as fibrous aggregates or radial clusters. Its appearance is typical for many amphiboles – a dark, almost black color and a vitreous luster on crystal faces. It is opaque. ## Physical Properties It is characterized by a hardness ranging from 5-6 on the Mohs scale. It has a vitreous luster and is relatively brittle. The mineral's density is approximately 3.35 g/cm³. ## Colors and Varieties This mineral occurs in black, and in thin splinters, it may appear greenish-black. No color or commercial varieties have been distinguished. ## History and Name The mineral's name reflects its chemical composition: "potassic" indicates the dominance of potassium, "ferro" indicates the presence of ferrous iron (Fe²⁺), and "ferri" indicates the presence of ferric iron (Fe³⁺). "Taramite" is the root name for this mineral series. It was formally described as a new mineral species relatively recently, following detailed chemical and crystallographic studies of amphiboles. ## Uses Potassic-ferro-ferri-taramite has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare and well-defined member of the amphibole group.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Greenish-black
Density: 3.35
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying potassic-ferro-ferri-taramite based on visual characteristics is practically impossible and requires advanced analytical techniques such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD). In collecting conditions, it is identified based on a label from a confirmed locality. ## Distinguishing from Similar Minerals It is visually indistinguishable from other black amphiboles, such as hornblende, arfvedsonite, riebeckite, or other taramites. The differences lie in the precise proportions of sodium, calcium, potassium, magnesium, and iron in the crystal structure, which cannot be determined without specialized equipment. ## Crystal Forms It forms elongated, columnar, or acicular crystals with a hexagonal cross-section. It often occurs as fibrous, matted, or radial aggregates.

Geological environment

## Genesis Potassic-ferro-ferri-taramite is a metamorphic mineral. It forms under conditions of regional metamorphism, in rocks such as phyllites and mica schists that have undergone sodic metasomatism. It is a product of transformations at medium temperatures and pressures. ## Mineral Associations It most commonly co-occurs with albite, quartz, epidote, chlorite, actinolite, titanite, and other amphiboles. At its type locality (Sesilia, Spain), it was found in association with albite, quartz, and epidote. ## Localities The most important and type locality for this mineral is the Sesilia quarry in the municipality of Murias de Paredes, León, Spain. This is currently the only confirmed and thoroughly described locality in the world.

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of potassic-ferro-ferri-taramite specimens primarily depends on well-formed crystals and their size. The most prized specimens are those with distinct, individual, terminated crystals or aesthetic, radial aggregates on a light rock matrix (e.g., on albitite). The certainty of identification from the type locality is also crucial. ## Popular Localities The only source of collector specimens is the Sesilia quarry in Spain. Specimens from this location are sought after by collectors specializing in mineral systematics and rare species.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. For heavier soiling, compressed air can be used. Avoid contact with water and any chemical agents. ## What to Avoid The mineral is sensitive to acids, which can damage it. Avoid ultrasonic cleaners, sudden temperature changes, and prolonged exposure to moisture. ## Storage It is recommended to store specimens in a dry place, in closed boxes or display cases, to protect them from dust and mechanical damage. Due to its brittleness, avoid placing it in direct contact with harder minerals.

Sources

IMA Mineral List (CNMNC)