Magnesio-ferri-fluoro-hornblende

Chemical formula: &#₉₇₄₄;Ca₂(Mg₄Fe₃+)(Si₇Al)O₂₂F₂

A rare amphibole from the hornblende group, distinguished by the simultaneous presence of magnesium, ferric iron, and fluorine in its structure.

## Characteristics Magnesio-ferri-fluoro-hornblende is a complex chain silicate belonging to the amphibole supergroup. It is an extremely rare mineral, found as small, poorly formed crystals or grains within the host rock. It typically occurs as embedded, prismatic crystals with an elongated habit, rarely exceeding a few millimeters in length. Due to its rarity and small crystal size, it is a mineral of primarily scientific and collector's interest. ## Physical Properties This mineral is characterized by a vitreous luster and is usually opaque or at most translucent on thin edges. Its Mohs hardness is approximately 6, which is typical for amphiboles. The density is estimated at about 3.23 g/cm³. ## Colors and Varieties Magnesio-ferri-fluoro-hornblende is observed in colors ranging from dark green to almost black. No distinct color varieties or commercial forms have been identified. ## History and Name The mineral's name, approved by the International Mineralogical Association (IMA) in 2013, reflects its chemical composition. The prefix "Magnesio" indicates the dominance of magnesium, "ferri" refers to the presence of iron in the trivalent oxidation state (Fe³⁺), "fluoro" to the dominance of fluorine over hydroxyl groups, and "hornblende" to its belonging to the hornblende group. The mineral was first described based on material from the Norra Kärr alkaline complex in Sweden.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: Gray
Density: 3.23
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying this mineral is extremely difficult and impossible without advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD). In field conditions or in a collection, it is indistinguishable from other dark amphiboles, such as common hornblende, arfvedsonite, or aegirine. ## Distinguishing from similar minerals Distinguishing it from other black or dark green amphiboles (e.g., fluoro-edenite, magnesiohastingsite) requires confirmation of the dominance of magnesium, ferric iron, and fluorine in specific structural positions, which is only possible in a laboratory. ## Crystal forms The mineral forms columnar or prismatic crystals, often with a hexagonal cross-section, typical of amphiboles. They usually occur as embedded grains or small, imperfectly formed crystals within the rock.

Geological environment

## Genesis Magnesio-ferri-fluoro-hornblende is a mineral of alkaline igneous rocks, rich in fluorine. It forms in the late stages of magma crystallization under conditions of elevated fluorine activity. The type locality (Norra Kärr) is a nepheline syenite. ## Mineral associations At the type locality in Sweden, it co-occurs with aegirine, eudialyte, microcline, nepheline, rosenbuschite, and titanite. Its occurrence with other minerals rich in fluorine and rare earth elements is characteristic of this environment. ## Localities The only confirmed and detailed described locality of this mineral worldwide is the Norra Kärr alkaline complex, located south of Lake Vättern in the province of Småland, Sweden.

Rarity

Extremely rare

For collectors

## Quality criteria Due to its extreme rarity, every analytically confirmed specimen is valuable to specialized collectors and scientific institutions. Specimens with well-formed, macroscopically visible crystals, clearly embedded in a contrasting rock matrix, would be most highly prized. Purity or color are of secondary importance compared to the mere fact of the mineral's confirmed presence. ## Popular localities The only source of specimens is the historical type locality in Norra Kärr, Sweden. Obtaining new material is practically impossible.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its rarity and potential instability, the use of water, and especially chemical agents, is discouraged. ## What to avoid Avoid contact with acids and other chemicals that may react with the mineral's complex composition. Do not heat specimens or subject them to ultrasound. Prolonged exposure to strong sunlight is not recommended. ## Storage It is recommended to store specimens in stable conditions, in closed display boxes, to protect them from dust, mechanical damage, and sudden changes in humidity. As a brittle mineral, it should be kept separate from harder specimens.

Sources

IMA Mineral List (CNMNC)