Potassic-fluoro-pargasite
Chemical formula: KCa₂(Mg₄Al)Si₆Al₂O₂₂F₂
Potassic-fluoro-pargasite is a rare mineral from the amphibole group, distinguished by the presence of potassium and fluorine in its structure.
Properties
- Mohs hardness
- 6.5
- Color
- Brownish-black
- Luster
- Vitreous
- Streak
- Pale-grey
- Density
- 3.46
- Cleavage
- perfect {110}
- Fracture
- Splintery
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Field identification of potassic-fluoro-pargasite is practically impossible without advanced studies. In a collection, it can be preliminarily recognized by its prismatic crystal habit and the characteristic amphibole cleavage angle (approx. 124°/56°). Final confirmation requires chemical analysis (EDS/WDS) to confirm the presence of potassium and fluorine. ## Distinguishing from Similar Minerals The mineral is visually indistinguishable from other light-colored amphiboles, such as pargasite, tremolite, or edenite. The differences lie in the chemical composition – pargasite contains sodium instead of potassium and hydroxyl groups instead of fluorine. Tremolite does not contain aluminum in such quantities. Without chemical analysis, differentiation is impossible. ## Crystal Forms It most often forms well-developed, prismatic or columnar crystals, often with a hexagonal cross-section. It also occurs as granular, fibrous, or radial aggregates.
Geological environment
## Genesis Potassic-fluoro-pargasite is a metamorphic mineral. It forms under high-grade metamorphic conditions, in the amphibolite and granulite facies, in calcium- and magnesium-rich rocks such as marbles, skarns, or calc-silicate rocks. Its crystallization occurs at high temperatures and pressures, in a potassium- and fluorine-rich environment. ## Mineral Associations It often co-occurs with minerals such as calcite, dolomite, diopside, forsterite, spinel, phlogopite, titanite, and other amphiboles and pyroxenes. ## Localities The most known and classic locality (type locality) of this mineral is in the Pargas region of Finland. Occurrences have also been reported in Sweden (e.g., in the Långban and Jakobsberg mines), Italy (Mount Somma, Vesuvius complex), USA (New York and New Jersey states), and Tajikistan (Pamir).
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with well-formed, sharply terminated, transparent crystals with a distinct color (e.g., pale green or blue). The size of the crystals and their setting on a contrasting rock matrix, such as white marble, are important. Specimens from classic, historical localities, like Pargas, are particularly sought after. ## Popular Localities Collector-grade specimens mainly come from Finland (Pargas), Sweden (Långban), and some localities in the USA, such as Franklin, New Jersey.
Care and storage
## Cleaning Specimens should be cleaned exclusively with lukewarm distilled water and a very soft brush or paintbrush. Ultrasonic cleaners should be avoided, as they can damage crystals along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids, especially hydrofluoric acid. Sudden temperature changes and prolonged exposure to intense sunlight should be avoided, although it is not considered particularly harmful. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to protect them from scratching by harder minerals (e.g., quartz). They should be protected from dust and moisture.