Dachiardite-Na

Chemical formula: Na₄(Si₂₀Al₄)O₄₈·₁₃H₂O

Dachiardite-Na is a zeolite group mineral, forming characteristic acicular crystals, often gathered in radial, spherical aggregates.

## Characteristics Dachiardite-Na is a hydrated sodium aluminosilicate belonging to the zeolite group. Typical specimens consist of thin, acicular or hair-like crystals, which often form radial aggregates resembling spheres or fans. Crystals can also be prismatic. Its appearance is delicate, and aggregates can reach several centimeters in diameter. ## Physical Properties This mineral is relatively soft, with a hardness of 4-4.5 on the Mohs scale. It has a vitreous luster, and a pearly luster on cleavage surfaces. It is transparent to translucent. Its density is approximately 2.14-2.21 g/cm³, making it a light mineral. ## Colors and Varieties Dachiardite-Na is most commonly colorless or white. It can also take on pinkish or yellowish hues. There are no distinct commercial varieties, and classification is based on the dominant cation (in this case, sodium, Na). ## History and Name The name "dachiardite" was given in 1906 in honor of Antonio D'Achiardi (1839-1902), an Italian professor of mineralogy at the University of Pisa. The suffix "-Na" was added in 1997 after the redefinition of the dachiardite group by the International Mineralogical Association (IMA) to distinguish it from the calcium variant (Dachiardite-Ca). ## Uses Due to its rarity in large quantities, dachiardite-Na has no industrial applications. However, it is a valued collector's mineral.

Properties

Mohs hardness: 4-4.5
Luster: Vitreous, Pearly
Streak: White
Density: 2.14-2.21
Cleavage: Perfect on {100}, Good on {001}
Fracture: Conchoidal to Uneven
Transparency: Transparent to Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key identifying features are its forms of occurrence – radial aggregates of acicular crystals, often in spherical shapes. Occurrence in vugs of volcanic rocks or pegmatites in association with other zeolites is a strong indicator. ## Distinguishing from Similar Minerals It can be confused with other acicular zeolites, such as mordenite or natrolite. Mordenite more often forms cotton-like aggregates, and its crystals are usually thinner and more tangled. Natrolite has crystals with a square cross-section. Final distinction from the very similar dachiardite-Ca requires chemical analysis. ## Crystal Forms It forms elongated, prismatic or acicular crystals, often with pointed terminations. The most characteristic are radial, spherulitic ("snowball") and fan-shaped aggregates.

Geological environment

## Genesis It forms under low-temperature hydrothermal activity. It fills gas vesicles and fractures in volcanic rocks, such as andesites and basalts. It is also found in miarolitic cavities in granitic pegmatites and in alpine-type veins. ## Mineral Associations It often co-occurs with other zeolite minerals, such as mordenite, ferrierite, clinoptilolite, stilbite, as well as with quartz (chalcedony), calcite, and opal. ## Localities Significant localities for dachiardite-Na include Austria (Tanzenberg tunnel, Styria - type locality), Italy (Fassa Valley, Trentino-Alto Adige), USA (Cape Lookout, Oregon), and Australia (Flinders, Victoria), from where famous spherical aggregates originate.

Rarity

Not very common

For collectors

## Quality Criteria Specimens with well-formed, spherical or fan-shaped aggregates with distinct luster are most highly valued. The absence of damage to delicate crystals and aesthetic placement on the rock matrix are important. Colorless and white specimens are standard, and a delicate pinkish hue enhances attractiveness. ## Popular Localities The most sought-after by collectors are the dachiardite "snowballs" from Flinders, Australia. Classic specimens also come from the Italian and Austrian Alps.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to Avoid The mineral is sensitive to high temperatures, which can cause dehydration and destruction of its structure. Contact with acids and strong detergents should be avoided. It is brittle and susceptible to mechanical damage. ## Storage It is best stored in closed boxes or display cases, protected from dust and shocks. It does not require special light protection, but extreme conditions should be avoided.

Sources

IMA Mineral List (CNMNC)