Ferro-pedrizite

Chemical formula: LiLi₂(LiFe²⁺₂Fe³⁺Al)Si₈O₂₂(OH)₂

Dark blue or violet-blue, rare mineral from the lithium amphibole group, discovered in Tuva, Russia.

## Characteristics Ferro-pedrizite is a rare silicate from the amphibole group, belonging to the pedrizite series. It forms elongated, prismatic crystals or fibrous aggregates. Its most distinctive feature is its intense, dark color, ranging from grayish-blue to violet-blue, which sets it apart from the host rock. ## Physical Properties This mineral is characterized by a hardness of 6 on the Mohs scale and a density of approximately 3.13 g/cm³. It has a vitreous luster and is translucent. Its fracture is splintery, and its streak is pale gray. ## Colors and Varieties Ferro-pedrizite occurs in a limited color range, including shades of dark grayish-blue and violet-blue. No named color varieties or commercial varieties are distinguished. ## History and Name The name "ferro-pedrizite" refers to the dominance of iron (ferro) in its chemical composition and its relation to other minerals in the pedrizite group. It was described and recognized as a new mineral relatively recently, and its type locality is the Sangilen Plateau in the Republic of Tuva, Russia. ## Applications Due to its rarity, ferro-pedrizite has no industrial applications. It is solely an object of scientific and collector interest for advanced collectors specializing in rare minerals or amphibole systematics.

Properties

Mohs hardness
6-0
Luster
Vitreous
Streak
Pale gray
Density
3.13
Cleavage
Perfect cleavage on (110) and a less perfect one on (001).
Fracture
Splintery
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Ferro-pedrizite can be identified by its characteristic dark blue or violet-blue color, prismatic crystal habit, and occurrence in a specific geological environment. A pale gray streak and splintery fracture are additional auxiliary features. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as riebeckite or arfvedsonite. Definitive differentiation requires advanced analytical methods, such as chemical analysis (EDS/WDS) or X-ray diffraction (XRD), due to subtle differences in composition and structure. ## Crystal Forms It most commonly forms elongated, columnar, or acicular crystals. It also occurs as fibrous or radial aggregates, embedded in the host rock.

Geological environment

## Genesis This is a mineral of metamorphic origin. It forms under conditions of regional metamorphism, in rocks rich in sodium and lithium, such as certain varieties of crystalline schists and gneisses. ## Mineral Associations In its type locality, it coexists with minerals such as quartz, albite, microcline, aegirine, riebeckite, and other rare amphiboles and silicates. ## Localities The most important and well-documented occurrence of ferro-pedrizite is its type locality – the Sangilen Plateau in the Republic of Tuva, Siberia, Russia. It is a very rarely found mineral in other parts of the world.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharply terminated crystals of intense, violet-blue color. Contrast with a light host rock (matrix) on which the crystals are embedded enhances their attractiveness. Crystal size and the richness of aggregates are also important. ## Popular Localities The only source of valuable collector specimens is the Sangilen Plateau in Russian Tuva. Specimens from this locality are the standard for this mineral.

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 chemical agents. ## What to Avoid The mineral is sensitive to acids and other chemicals. It should be protected from sudden temperature changes and prolonged exposure to direct sunlight, which can affect its color. ## Storage It is recommended to store specimens in stable conditions, in closed display boxes or cabinets, away from dust and moisture. Due to the presence of perfect cleavage, it should be protected from impacts and vibrations.

External references

Sources

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