Eckermannite

Chemical formula: NaNa₂(Mg₄Al)Si₈O₂₂(OH)₂

A rare mineral from the amphibole group, forming prismatic or fibrous crystals of green, blue-green, or black color.

## Characteristics Eckermannite is a rare silicate from the sodium amphibole group, representing an end-member of an isomorphic series. It forms elongated, prismatic crystals, often occurring as fibrous, radial, or asbestiform aggregates. Granular masses are less common. Specimens typically have an intense green, blue-green, or almost black color, which is characteristic of sodium- and iron-rich amphiboles. ## Physical Properties This mineral has a hardness ranging from 5-6 on the Mohs scale and a density of 3.05 to 3.23 g/cm³. It exhibits a vitreous luster, and on fracture surfaces, it can be dull. It is a brittle, translucent mineral, and in thin splinters or fibers, it can be transparent. ## Colors and Varieties The dominant colors of eckermannite are various shades of green, from emerald green to dark green, as well as blue-green, gray-green, and black. Its color is strongly dependent on its iron content. No commercial or color varieties are distinguished. ## History and Name The mineral's name, given in 1942 by Nils Sundius, honors the Swedish industrialist, geologist, and petrographer Harry von Eckermann (1886-1969), who studied the alkaline rocks of the Norra Kärr complex in Sweden, where this mineral was first identified. ## Uses Eckermannite has no industrial applications. It is solely an object of scientific interest and is a prized collector's mineral due to its rarity and attractive forms of occurrence.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Pale gray
Density: 3.05-3.23
Cleavage: Perfect on {110}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying eckermannite based on visual characteristics is extremely difficult, and often impossible without advanced analysis. A key indicator is its occurrence environment – almost exclusively alkaline rocks. The characteristic crystal habit (long prisms, fibers) and color (green to black) are also helpful. ## Distinguishing from Similar Minerals Eckermannite is macroscopically indistinguishable from other sodium amphiboles, such as arfvedsonite, magnesio-arfvedsonite, richterite, or fluoro-richterite. All these minerals have similar color, crystal habit, and physical properties. Definitive differentiation requires chemical analysis (e.g., EDS, WDS) or X-ray diffraction (XRD). ## Crystal Forms Eckermannite crystals are typically long-prismatic, acicular, or fibrous. They form radial aggregates, tangled aggregates (felted, asbestiform), or occur as embedded grains in the host rock.

Geological environment

## Genesis Eckermannite is a characteristic mineral of alkaline-rich and silica-poor igneous rocks, such as nepheline syenites and their associated pegmatites. It also forms during sodium metasomatism (fenitization) in contact zones of alkaline intrusions and carbonatites. It is less commonly found in metamorphic rocks of the glaucophane facies. ## Mineral Associations This mineral often co-occurs with other minerals typical of alkaline environments, such as albite, microcline, nepheline, aegirine, arfvedsonite, richterite, eudialyte, lorenzenite, as well as fluorite and zircon. ## Localities The most important eckermannite localities worldwide include its type locality in Norra Kärr, Sweden. Additionally, high-quality specimens come from the alkaline complexes of Mont Saint-Hilaire in Canada, the Khibiny and Lovozero massifs on the Kola Peninsula in Russia, and the Ilímaussaq complex in Greenland.

Rarity

Rare

For collectors

## Quality Criteria Well-formed, terminated crystals with intense, vibrant color are most valued by collectors. Specimens where eckermannite forms aesthetic compositions with other rare minerals, such as eudialyte or lorenzenite, are also highly regarded. Crystal size and the richness of aggregates also significantly influence the attractiveness of a specimen. ## Popular Localities Specimens from Mont Saint-Hilaire in Canada are considered among the best for collectors, often characterized by excellent crystal development. Russian localities on the Kola Peninsula also provide specimens with vibrant color and interesting mineral associations.

Care and storage

## Cleaning Eckermannite specimens should be cleaned carefully, using a soft brush and lukewarm water, possibly with a mild soap. After washing, rinse thoroughly with distilled water and allow to dry completely. Fibrous aggregates are particularly delicate and susceptible to mechanical damage. ## What to Avoid The mineral is sensitive to acids, especially hydrofluoric acid. Ultrasonic cleaners should be avoided, as they can cause fragile or fibrous aggregates to disintegrate. It should also not be exposed to rapid temperature changes. ## Storage It is recommended to store specimens in closed boxes or display cases to protect them from dust and mechanical damage. Particularly fragile, fibrous specimens should be secured in the box to prevent crumbling during handling.

Sources

IMA Mineral List (CNMNC)