Dachiardite-K

Chemical formula: K₄(Si₂₀Al₄)O₄₈·₁₃H₂O

Dachiardite-K is a rare mineral from the zeolite group, forming colorless or white, acicular crystals in vesicles and fissures of volcanic rocks.

## Characteristics Dachiardite-K is the potassium-dominant member of the dachiardite series, belonging to the zeolite group. It typically occurs as fine, acicular or fibrous crystals, which form radial aggregates, fans, or spherical clusters. Individual crystals are often too small to be seen with the naked eye, and the clusters appear as delicate, white or colorless spheres and bundles. ## Physical Properties Dachiardite-K crystals are characterized by a vitreous or silky luster. They are transparent to translucent. The hardness on the Mohs scale is approximately 4-4.5, and the density is low, typical for zeolites, at about 2.22 g/cm³. ## Colors and Varieties This mineral is most commonly colorless or white. No colored or commercial varieties are distinguished. ## History and Name The name "dachiardite" was given in 1906 by the Italian mineralogist Giovanni D'Achiardi in honor of his father, Antonio D'Achiardi, also a mineralogist and professor at the University of Pisa. The suffix "-K" refers to the dominance of potassium (K) in its chemical composition and was added in 1997 as part of a revision of zeolite nomenclature to distinguish this mineral from its sodium counterpart, dachiardite-Na. ## Applications Due to its rarity and microscopic crystal sizes, dachiardite-K has no industrial applications. It is of purely scientific and collector's interest.

Properties

Mohs hardness: 4
Color: Snow-white
Luster: Vitreous, Silky
Streak: White
Density: 2.18
Cleavage: (100)
Fracture: Step-Like
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of dachiardite-K is based on its characteristic mode of occurrence – radial or spherical aggregates composed of very fine, acicular crystals. Its typical geological environment, i.e., voids in volcanic rocks, is also indicative. However, definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other acicular zeolites, such as natrolite, mesolite, scolecite (natrolite group), or mordenite. Zeolites from the natrolite group are usually more brittle and have a different crystal cross-section (square). Mordenite forms similar clusters, but they are often more "woolly" or "felt-like." A certain distinction without specialized equipment is practically impossible. ## Crystal Forms Crystals are elongated along the b-axis, forming acicular or fibrous shapes. They usually occur as radial aggregates, fans, and also spherulites (spherical clusters) lining the interiors of gas vesicles.

Geological environment

## Genesis Dachiardite-K is a low-temperature hydrothermal mineral. It forms during crystallization from aqueous solutions in the final stages of volcanic activity. It fills gas vesicles (amygdules) and fissures in acidic and intermediate volcanic rocks, such as rhyolites, trachytes, and andesites. ## Mineral Associations It often co-occurs with other zeolites, such as mordenite, ferrierite, clinoptilolite, as well as with quartz (including chalcedony and opal) and calcite. ## Localities Key localities for dachiardite-K worldwide include Tanohata and Yugawara in Japan; Mount Adamello and Val di Fassa in Italy; Teigarhorn in Iceland; and some locations in Oregon and Arizona in the USA. In Poland, its occurrence has been noted in melaphyres in the Lubiechowa area in Lower Silesia.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those where the spherical or radial aggregates of dachiardite-K are well-formed, clearly separated from each other, and contrast with the color of the host rock (matrix). The absence of damage to the delicate needles is important. Due to the small size of the crystals, these specimens are the domain of collectors specializing in microminerals ("micromounts"). ## Popular Localities Classic and most sought-after localities include those in Japan (Tanohata, Yugawara), which have yielded very aesthetic, spherical aggregates. Specimens from Iceland and Italy are also valued.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a soft brush, avoiding prolonged soaking of the specimen. After cleaning, it should be thoroughly dried at room temperature. ## What to Avoid Avoid contact with acids and other chemicals that can damage delicate crystals. The mineral is sensitive to high temperatures, which can cause water loss from its structure (dehydration) and crystal damage. It should not be cleaned in ultrasonic cleaners. ## Storage Dachiardite-K specimens are very fragile and brittle. They are best stored in closed, padded boxes (e.g., "micromount" type) to protect them from mechanical damage and dust. Avoid areas with high humidity or sudden temperature changes.