Potassic-ferro-ferri-sadanagaite
Chemical formula: KCa<sub>2</sub>(Fe<sup>2+</sup><sub>3</sub>Fe<sup>3+</sup><sub>2</sub>)(Si<sub>5</sub>Al<sub>3</sub>)O<sub>22</sub>(OH)<sub>2</sub>
Potassic-ferro-ferri-sadanagaite is a very rare, black amphibole group mineral, found in iron-rich skarns and gneisses.
Properties
- Mohs hardness
- 5-6
- Luster
- Vitreous
- Streak
- Gray
- Density
- 3.45
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Field identification of this mineral is practically impossible and requires advanced analytical methods, such as chemical analysis (EDS/WDS) and X-ray diffraction (XRD). In a collection, it can be preliminarily recognized by its black color, prismatic habit, and co-occurrence with minerals typical of skarns. ## Distinguishing from Similar Minerals It can be confused with other black amphiboles (e.g., hornblende, arfvedsonite) or pyroxenes (e.g., augite). Differentiation is almost exclusively possible based on detailed laboratory analyses that confirm its unique chemical composition with a dominance of potassium and both forms of iron. ## Crystal Forms It forms columnar or prismatic crystals, often with a granular habit. It usually occurs as aggregates or as individual grains embedded in the host rock.
Geological environment
## Genesis This is a metamorphic mineral, forming under high-temperature conditions. It forms in iron-rich skarns created at the contact of alkaline syenite intrusions with iron formations, and in biotite-amphibole gneisses. ## Mineral Associations It most commonly co-occurs with minerals such as: diopside, hedenbergite, andradite, magnetite, ilmenite, apatite, titanite, biotite, plagioclase, and microcline. ## Localities Confirmed occurrences of this mineral are few. The most important is the type locality in Kovdor on the Kola Peninsula in Russia. It is also known from the Ilímaussaq alkaline complex in Greenland and from Sagåsen in Norway.
Rarity
Very rare
For collectors
## Quality Criteria The most valuable specimens are those with well-formed, visible crystals, contrasting with a light host rock. Due to its rarity, every analytically confirmed specimen holds significant value for specialized collectors of rare and systematic minerals. ## Popular Localities The most known and prized specimens come from the Kovdor massif on the Kola Peninsula in Russia, which is its type locality.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. The use of water or any chemical agents is not recommended, as the mineral may react with acids. ## What to Avoid Avoid contact with chemicals, especially acids. Do not expose it to ultrasound or sudden temperature changes. Store away from moisture. ## Storage Specimens should be stored in stable conditions, in a dry place, preferably in a closed display box, to protect them from dust and mechanical damage. Due to its brittleness, avoid placing it in contact with harder minerals.