Ferri-taramite

Chemical formula: Na(NaCa)(Mg₃Fe₃+₂)(Si₆Al₂)O₂₂(OH)₂

Ferri-taramite is a rare, dark green or black sodium amphibole, occurring as prismatic crystals in metamorphic rocks.

## Characteristics Ferri-taramite is a complex silicate from the amphibole group, classified as a sodium amphibole. It forms elongated, prismatic crystals, often terminated by flat faces, as well as fibrous or granular aggregates. Its color is typically dark green, greenish-brown to almost black. It is an opaque mineral with a vitreous luster on crystal faces. ## Physical Properties It is characterized by a hardness ranging from 5-6 on the Mohs scale. It has a vitreous luster and is a relatively brittle mineral. Its density is approximately 3.26 g/cm³. It exhibits perfect cleavage in two directions, typical of amphiboles, intersecting at angles of approximately 56° and 124°. ## Colors and Varieties This mineral occurs in shades from dark green and greenish-brown to black. No distinct color varieties or commercial varieties are recognized. ## History and Name The name "ferri-taramite" refers to its chemical composition – the dominance of ferric iron (ferri) – and its relation to another mineral from the amphibole group, taramite. It was formally described and recognized as a distinct mineral species relatively recently, as part of the amphibole classification revision. ## Applications Ferri-taramite has no industrial significance. Its occurrence is solely of scientific and collecting interest for those specializing in the systematics of rock-forming minerals.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Greenish-gray
Density: 3.26
Cleavage: Perfect, on {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Ferri-taramite is difficult to identify visually without advanced analytical techniques. Preliminary identification is possible based on its dark color (greenish-black, black), prismatic crystal habit, and amphibole-typical cleavage angles of ~56/124°. It occurs in specific metamorphic rocks, which is an important clue. ## Distinguishing from Similar Minerals It can easily be confused with other black amphiboles, such as hornblende, arfvedsonite, or riebeckite, as well as pyroxenes (e.g., augite). Differentiation from hornblende or augite is possible based on cleavage angles (pyroxenes have angles close to 90°). Definitive identification and differentiation from other sodium amphiboles require chemical analysis (EDS/WDS) or diffraction methods (XRD). ## Crystal Forms It most commonly forms columnar or prismatic crystals, which can reach several millimeters in length. It also occurs as granular, fibrous, or radial aggregates within the host rock.

Geological environment

## Genesis Ferri-taramite is a rock-forming mineral that forms under conditions of regional metamorphism, particularly in the amphibolite facies and greenschist facies. It forms in rocks rich in sodium and iron, such as amphibolites, gneisses, and glaucophane schists. ## Mineral Associations It often co-occurs with minerals such as albite, epidote, chlorite, quartz, actinolite, crossite, as well as other amphiboles and pyroxenes. The presence of these minerals is crucial for determining the conditions of its formation. ## Localities Confirmed occurrences of this mineral are few. It has been identified, among other places, in the ultramafic complex near the village of Uklina in the Ukrainian Carpathians (type locality), as well as in some metamorphic rocks in Austria and Italy. It is a widely distributed mineral as a rock component, but rarely identified and found in the form of well-developed specimens.

Rarity

Very rare

For collectors

## Quality Criteria For collectors specializing in mineral systematics, the most valuable specimens are those with well-formed, sharp crystals with distinct luster, set on a contrasting rock matrix. Precisely determined locality and confirmed mineral identification through chemical analysis are also important, significantly increasing the scientific and collectible value of the specimen. ## Popular Localities The most scientifically valued specimens come from the type locality in Ukraine. Due to identification difficulties and a lack of visual appeal for the average collector, ferri-taramite is not a popular mineral on the market and rarely appears in trade.

Care and storage

## Cleaning Ferri-taramite specimens can be cleaned with a soft, dry brush to remove dust. If necessary, distilled water may be used, after which the specimen should be thoroughly dried. Ultrasonic cleaners should be avoided, as they can damage brittle crystals. ## What to Avoid Contact with strong acids and bases, which can react with the mineral, should be avoided. Ferri-taramite is stable under normal conditions, but it should be protected from sudden temperature changes and mechanical damage due to its cleavage. ## Storage Specimens should be stored in separate, padded boxes or display cases to prevent scratches and chipping. It does not require special conditions regarding light or humidity, but standard room conditions are recommended.

Sources

IMA Mineral List (CNMNC)