Erionite-Na

Chemical formula: Na₁₀(Si₂₆Al₁₀O₇₂)·₃₀H₂O

Erionite-Na is a hydrated sodium aluminosilicate from the zeolite group, forming characteristic fibrous aggregates with a silky luster.

## Characteristics Erionite-Na is a mineral belonging to the zeolite group, specifically to the erionite subgroup. It typically forms acicular or fibrous crystals, which often coalesce into woolly or felt-like aggregates. Individual crystals are usually too small to be seen with the naked eye, but their clusters have a characteristic fluffy appearance. Specimens are usually white or colorless. ## Physical Properties Erionite-Na crystals are flexible and have a hardness of about 3.5-4 on the Mohs scale. This mineral is characterized by low density, typical for zeolites. The luster of fibrous aggregates is silky, while individual, better-formed crystals may exhibit a vitreous luster. ## Colors and Varieties Erionite-Na occurs almost exclusively in white or is colorless. No colored or commercial varieties are distinguished. The name "Erionite-Na" indicates the dominance of sodium (Na) in the chemical composition within the erionite series, where sodium can be replaced by potassium (Erionite-K) or calcium (Erionite-Ca). ## History and Name The name "erionite" comes from the Greek word "erion" (ἔριον) meaning "wool," which is a direct reference to the appearance of its fibrous aggregates. The mineral was first described in 1898 by Arthur S. Eakle. The suffix "-Na" was added later as part of the erionite group mineral systematics to indicate the dominant cation – in this case, sodium. ## Uses Due to its molecular structure, erionite (like other zeolites) has been studied for applications in catalysis and as a molecular sieve. However, its fibrous nature, similar to asbestos, classifies it as a human carcinogen (Group 1 according to IARC). For this reason, its commercial use is very limited, and its main role is confined to being an object of scientific and collector interest.

Properties

Mohs hardness: 3.5-4
Luster: Vitreous, Silky
Streak: White
Density: 2.02-2.13
Cleavage: Good on {1010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Hexagonal

Diagnostic features

## Identification The key diagnostic feature of erionite-Na is its woolly, felt-like, or fluffy aggregates composed of very fine, white fibers. The silky luster of these clusters is also characteristic. It occurs in cavities and fissures of volcanic rocks, which is an important field indicator. ## Distinguishing from Similar Minerals Erionite-Na can be confused with other fibrous zeolites, such as natrolite, mesolite, or scolecite. Typically, erionite fibers are finer and form more "woolly" clusters than the aforementioned minerals, whose crystals can be coarser and more often form radial aggregates. It can also be confused with asbestos, but erionite usually forms clusters in geodes and gas vesicles, not in veins. Final differentiation requires advanced analytical methods (e.g., XRD). ## Crystal Forms Erionite-Na crystallizes in the form of very thin, elongated, acicular or hair-like crystals with a hexagonal cross-section. These crystals almost always occur as dense, tangled clusters and aggregates of a fibrous, felt-like, or woolly nature, filling voids in the host rock.

Geological environment

## Genesis Erionite-Na is a secondary mineral, formed as a result of low-temperature hydrothermal processes or diagenesis. It forms in voids, gas vesicles, and fissures in basic volcanic rocks, such as basalts, andesites, or volcanic tuffs. It forms from the reaction of formation waters or groundwater with volcanic ash and volcanic glass. ## Mineral Associations Erionite-Na often co-occurs with other zeolites, such as chabazite, phillipsite, clinoptilolite, as well as with calcite, opal, quartz (chalcedony), and montmorillonite. ## Localities Significant occurrences of erionite-Na are found in many places around the world. Classic localities include the area around Durkee in Baker County (Oregon, USA), where it occurs in rhyolitic tuffs. It is also known from Romas, on the island of Gotland (Sweden), and from vesicles in basalts in Magheramorne (Northern Ireland). Other important occurrences include Maze (Niigata Prefecture, Japan) and some localities in Arizona and Nevada (USA).

Rarity

Not very common

For collectors

## Quality Criteria The collector appeal of erionite-Na depends on several factors. Most prized are specimens with well-defined, "fluffy" or woolly aggregates that completely fill a void in the host rock, creating an impressive "snowball" effect. The purity and whiteness of the fibers and the aesthetic contrast with the dark basaltic rock are important. Specimens where erionite co-occurs with other colorful minerals (e.g., chabazite) are also sought after. The size of the mineral-filled void matters, but the delicacy and intactness of the fibrous structure are key. ## Popular Localities Specimens from Oregon, USA, especially from the Durkee area, are considered the most classic and desirable by collectors. Samples from basalts in Northern Ireland and some localities in Japan are also highly valued.

Care and storage

## Cleaning Erionite-Na specimens are very brittle and delicate. They should only be cleaned using compressed air to remove dust. Contact with water is not recommended, as it can penetrate the porous structure and weaken the aggregate. The use of any mechanical tools, even soft brushes, risks irreversible damage to the delicate fibers. ## What to Avoid Absolutely avoid contact with water and any chemicals. Do not heat the specimen, as this can lead to the loss of structural water and destruction of the mineral. Avoid vibrations and shocks. Due to the carcinogenic nature of the fibers, avoid any activities that may lead to dusting (crushing, scratching, blowing). It is recommended to work with gloves and store in an enclosed space. ## Storage Specimens should be stored in closed, transparent containers (e.g., "membrane boxes" or display cases) that protect them from dust, mechanical damage, and accidental release of fibers into the environment. Display should only occur in a closed cabinet.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FErionite