Perlialite

Chemical formula: K<sub>9</sub>NaCa(Si<sub>24</sub>Al<sub>12</sub>)O<sub>72</sub>·15H<sub>2</sub>O

A rare zeolite with a spherulitic habit, forming white, radial aggregates in cavities of volcanic rocks.

## Characteristics Perlialite is a hydrated potassium, sodium, and calcium aluminosilicate, belonging to the zeolite group. It occurs as small, spherulitic (spherical) aggregates with a radial, fibrous internal structure. Individual "fibers" are actually elongated, acicular crystals. Aggregates rarely exceed a few millimeters in diameter and are most commonly found in gas vesicles and small fissures in volcanic rocks. ## Physical Properties Perlialite crystals are too small for standard hardness tests, but its hardness is estimated to be around 4-5 on the Mohs scale. The mineral exhibits a vitreous or silky luster on the fiber surfaces. It is translucent to opaque. The density is approximately 2.26 g/cm³. ## Colors and Varieties Perlialite is usually colorless or white. No colored or commercial varieties are distinguished. ## History and Name The mineral's name comes from Lina Perlingieri (1885-1975), an Italian mineral collector from Naples, who was the first to find this mineral. It was described and approved as a new mineral species in 1980 by Ermanno Franco. ## Uses Perlialite has no industrial application. It is solely a mineral of scientific and collecting importance, sought after by specialists collecting rare zeolites.

Properties

Mohs hardness
4-5
Luster
Vitreous, Silky
Streak
White
Density
2.26
Cleavage
Imperfect on {1010}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Characteristic features of perlialite are small, white or colorless, spherulitic aggregates with a silky luster and radial internal structure. Its occurrence in gas vesicles in volcanic rocks, especially in association with other zeolites, is a strong diagnostic indicator. However, final confirmation requires advanced analytical methods (XRD, EDS). ## Distinguishing from Similar Minerals Perlialite can be confused with other zeolites that form radial aggregates, such as natrolite, mesolite, scolecite (natrolite group), or thomsonite. Perlialite aggregates are usually smaller and have a silkier luster than the vitreous luster of members of the natrolite group. Unlike them, perlialite fibers do not exhibit perfect cleavage. Distinguishing it from thomsonite without chemical analysis is practically impossible. ## Crystal Forms This mineral forms almost exclusively spherulitic aggregates, composed of tightly packed, radially diverging acicular or fibrous crystals.

Geological environment

## Genesis Perlialite is a low-temperature hydrothermal mineral. It crystallizes in gas vesicles (amygdales) and fissures in alkaline volcanic rocks, such as phonolites and tephrites. It forms as a result of post-magmatic solution activity in the final stages of lava cooling. ## Mineral Associations This mineral often co-occurs with other zeolites, such as chabazite, phillipsite, gismondine, thomsonite, as well as calcite and apophyllite. At its type locality (Monte Somma), it was found in association with chabazite-K, phillipsite-K, and davyn. ## Localities The most important and type locality for perlialite is the Somma-Vesuvius volcanic complex in Italy, particularly quarries in the Pollena area. It is also known from several other localities worldwide, including the Khibiny Massif on the Kola Peninsula in Russia and the Eifel volcano in Germany.

Rarity

Very rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, distinct spherulites, contrastingly set on a dark rock matrix. The size of the aggregates is important – the larger, the more attractive the specimen. The presence of other rare minerals from the same locality is also significant. Specimens should be free from mechanical damage. ## Popular Localities By far the most sought-after and classic specimens come from the type locality, the Somma-Vesuvius complex in Italy. Specimens from this location are considered exemplary for this species.

Care and storage

## Cleaning Specimens should be cleaned mechanically only, using a soft brush to remove dust. Due to its delicate, fibrous structure, ultrasonic cleaners and strong jets of water should be avoided. If necessary, distilled water can be used, followed by thorough drying of the specimen with cool air. ## What to Avoid Contact with acids and other chemicals that can damage the zeolite structure should be avoided. As a hydrated mineral, perlialite is sensitive to high temperatures, which can lead to its dehydration and destruction. It should be protected from prolonged exposure to strong sunlight. ## Storage It is recommended to store specimens in closed, stable containers (e.g., micromount boxes) to protect them from dust, mechanical damage, and sudden changes in humidity. Fragile aggregates are prone to crumbling, so vibrations and shocks should be avoided.

Sources

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