Chabazite-K

Chemical formula: (K<sub>2</sub>NaCa<sub>0.5</sub>)Al<sub>4</sub>Si<sub>8</sub>O<sub>24</sub>·11H<sub>2</sub>O

Chabazite-K is a rare mineral from the zeolite group, a potassium analogue of chabazite-Ca, forming characteristic, almost cubic crystals.

## Characteristics Chabazite-K is a hydrated potassium, sodium, and calcium aluminosilicate, belonging to the chabazite series within the zeolite group. This mineral forms crystals with a characteristic, pseudorhombohedral or pseudocubic appearance, which are actually the result of twinned intergrowths of trigonal crystals. The crystals are often well-formed and grown on host rocks, forming attractive druses. They are usually small, rarely exceeding a few millimeters in size. ## Physical Properties Chabazite-K has a Mohs hardness of approximately 4.5. Its luster is vitreous. It is a relatively light mineral, with a density similar to other zeolites. Crystals are typically transparent to translucent. ## Colors and Varieties This mineral is most often colorless or white. No named color varieties or commercial varieties are distinguished. ## History and Name The name "chabazite-K" refers to its chemical composition – it is a member of the chabazite series in which potassium (K) is the dominant cation. It was formally recognized as a distinct mineral species by the International Mineralogical Association (IMA) in 1998, as part of a revision of zeolite nomenclature. Previously, these specimens were identified as a potassium variety of chabazite. ## Applications Chabazite-K, like other zeolites, has potential applications as a molecular sieve, catalyst, or in ion-exchange processes due to its porous crystal structure. However, due to its rarity, it has no industrial significance and is valued primarily as a collector's mineral.

Properties

Mohs hardness
4.5
Luster
Vitreous
Streak
White
Density
2.08-2.1
Cleavage
Distinct on {1011}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification The key diagnostic feature of chabazite-K is the form of its crystals – characteristic rhombohedra, which often look like slightly distorted cubes. This shape, combined with its occurrence in cavities of volcanic rocks and vitreous luster, is a strong indicator. However, definitive differentiation from other members of the chabazite series requires chemical analysis. ## Differentiation from Similar Minerals Chabazite-K is visually indistinguishable from other minerals in the chabazite series, such as chabazite-Ca, chabazite-Na, or chabazite-Sr. All form identical crystals. It can be confused with other zeolites of similar habit, e.g., analcime (which forms deltoidal icositetrahedral crystals) or apophyllite (which has perfect cleavage and often a pearly luster on one of its planes). ## Crystal Forms It most often occurs as single, well-formed rhombohedral crystals, often penetration-twinned, which gives them a pseudocubic appearance. It also forms granular aggregates and crystalline druses lining the interiors of gas vesicles.

Geological environment

## Genesis Chabazite-K is a mineral of hydrothermal origin. It forms at low temperatures, crystallizing in vesicles and fractures in volcanic rocks, such as basalts, andesites, and phonolites. It is a product of the alteration of primary rock-forming minerals under the influence of silica- and potassium-rich waters. ## Mineral Associations It often co-occurs with other zeolites, such as phillipsite, analcime, thomsonite, as well as with calcite and minerals from the smectite group. ## Localities Significant occurrences of chabazite-K are found in Italy, particularly in the Vesuvius area and the Vulsini volcanic complex (Lazio). It also occurs in Germany (Eifel), in Russia on the Kola Peninsula, and in some locations in the USA, e.g., in Oregon.

Rarity

Rare

For collectors

## Quality Criteria Most prized by collectors are specimens with sharp, well-formed, and transparent crystals that form contrasting druses on a small rock matrix. Crystal size is highly valued, although even millimeter-sized but perfectly formed crystals are attractive. Associations with other rare zeolites are also desirable. ## Popular Localities The best collector specimens of chabazite-K come from classic localities in Italy, such as the areas around Rome (e.g., Vallerano) and the Somma-Vesuvius volcanic complex. Specimens from these locations are considered exemplary for this mineral.

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 Avoid contact with acids, which can damage the mineral. Chabazite-K, as a zeolite, is sensitive to high temperatures, which can cause water loss from its structure and crystal destruction. It should not be heated or stored in very dry conditions. ## Storage Chabazite-K specimens are fragile and should be stored in separate boxes or display cases, away from harder minerals that could scratch them. They should be protected from dust and sudden temperature changes.

External references

Sources

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