Sodic-ferri-clinoferroholmquistite

Chemical formula: Na₀.₅Li₂Fe₂+₃Fe₃+₂Si₈O₂₂(OH)₂

Sodic-ferri-clinoferroholmquistite is a very rare, dark green to black mineral from the lithium amphibole group, occurring as acicular crystals.

## Characteristics Sodic-ferri-clinoferroholmquistite is a complex silicate from the lithium amphibole group, belonging to the clinoferroholmquistite series. It forms elongated, acicular or fibrous crystals, often gathered in radial or tangled aggregates. Its color is typically dark green, greenish-black to almost black. It is an opaque mineral with a vitreous luster. ## Physical Properties This mineral is characterized by a hardness in the range of 5-6 on the Mohs scale. It has a vitreous luster and is opaque. The calculated density is approximately 3.31 g/cm³. It exhibits perfect cleavage in two directions, typical for amphiboles. ## History and Name The mineral's name, approved by IMA in 2017 (IMA2017-059), refers to its chemical composition – the dominance of sodium (sodic), ferric iron (ferri), and its relation to clinoferroholmquistite. It was described based on material from its type locality in the Czech Republic.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Grayish green
Density: 3.31
Cleavage: Perfect on {210}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification The mineral is identified by its characteristic form – long, acicular or fibrous crystals of a dark green to black color. The occurrence environment (lithium pegmatites) and co-occurring minerals such as quartz, albite, lepidolite, or elbaite are also key. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as hornblende, riebeckite, or tourmaline (schorl). Differentiation often requires advanced analytical methods (chemical analysis, XRD), although crystal habit and paragenesis can be helpful. Unlike tourmaline, the crystals do not exhibit its typical rounded triangular cross-section. ## Crystal Forms Crystals are prismatic, strongly elongated along the c-axis, with an acicular or hair-like habit. They typically form fibrous, radial, or tangled aggregates.

Geological environment

## Genesis Sodic-ferri-clinoferroholmquistite is a mineral of magmatic origin. It forms in the late stages of crystallization of lithium- and sodium-rich granitic pegmatites, particularly in LCT-type (lithium-cesium-tantalum) pegmatites. ## Mineral Associations This mineral co-occurs with quartz, albite, microcline, lepidolite, elbaite (a variety of tourmaline), and other pegmatitic minerals. ## Localities The only confirmed and described locality (type locality) for this mineral is the lepidolite pegmatite quarry in Rožná, in the Žďár nad Sázavou district (Vysočina Region) in the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As an extremely rare mineral, any well-formed and correctly identified specimen is valuable. The most desirable specimens are those with distinct, undamaged acicular crystals forming aesthetic aggregates on a rock matrix, preferably accompanied by other pegmatitic minerals like lepidolite or elbaite. The size and richness of crystal clusters significantly increase collector value.

Care and storage

## Cleaning Due to the acicular or fibrous nature of the crystals, mechanical cleaning is risky. The safest method is to use compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a very soft brush, then thoroughly dry the specimen. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the mineral. Brittle, acicular crystals are very sensitive to impacts and vibrations. Do not clean specimens in ultrasonic cleaners. ## Storage Specimens should be stored in stable conditions, away from dust and moisture. It is best to place them in a closed display box with a soft lining to protect delicate crystals from mechanical damage.

Sources

IMA Mineral List (CNMNC)