Chabazite-Ca

Chemical formula: Ca₂Al₄Si₈O₂₄·₁₃H₂O

Chabazite-Ca is a common mineral from the zeolite group, forming characteristic, almost cubic rhombohedral crystals in cavities of volcanic rocks.

## Characteristics Chabazite-Ca is a hydrated calcium aluminosilicate belonging to the zeolite group. It forms some of the most recognizable crystals among minerals of this group. It most often occurs as well-formed, pseudocubic (cubic) rhombohedra, which can be single or twinned in groups. Crystals often exhibit simple or penetration twins. Crystal surfaces can be smooth and lustrous, though they may also be dull or corroded. Specimens typically grow on the walls of cavities and fissures in host rocks, forming impressive druses. ## Physical Properties Chabazite-Ca has a hardness of 4 to 5 on the Mohs scale, making it a relatively soft mineral. Its luster is typically vitreous. It is a brittle mineral, with an uneven or conchoidal fracture. The density is approximately 2.05-2.1 g/cm³, so it is relatively light. It can be transparent, translucent, or almost opaque, depending on its purity and degree of crystallization. ## Colors and Varieties Most often, it is colorless or white. However, it can take on various shades, including yellowish, pinkish, orange (salmon hue), greenish, or reddish-brown, which is usually caused by the presence of microscopic inclusions of other minerals, such as iron oxides. The trade name "acadiolite" was historically used for pink or reddish chabazites from Nova Scotia, Canada, but it is not a formally recognized variety. ## History and Name The name "chabazite" comes from the Greek word *chabazios* (or *chalazios*), meaning "hail," which was a reference to one of the twenty stones mentioned in the poem "Peri Lithos," attributed to Orpheus. This name was introduced to mineralogy by Louis-Augustin Bosc d'Antic in 1792. The suffix "-Ca" was added later to indicate calcium as the dominant cation in this particular variety of chabazite, in accordance with modern zeolite nomenclature. ## Uses Due to its porous molecular structure, chabazite (like other zeolites) has potential industrial applications as a molecular sieve, catalyst, or in ion exchange processes. It is also a valued and popular collector's mineral.

Properties

Mohs hardness: 4-5
Luster: Vitreous
Streak: White
Density: 2.05-2.1
Cleavage: Distinct/Good on {1011}
Fracture: Uneven to Conchoidal
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification The most characteristic feature of Chabazite-Ca is its rhombohedral crystals, which closely resemble cubes. They often occur as penetration twins. This mineral almost always forms in cavities and fissures of volcanic rocks, such as basalts or andesites. It reacts with hydrochloric acid, effervescing and gelatinizing. ## Distinguishing from Similar Minerals Chabazite is sometimes confused with other minerals that form cubic or pseudocubic crystals. It can be distinguished from calcite by its hardness (calcite is softer, 3 on the Mohs scale) and lack of perfect rhombohedral cleavage. From fluorite, it differs in hardness (fluorite has a hardness of 4, but perfect octahedral cleavage) and occurrence environment. Other zeolites, like apophyllite, form crystals with a different habit (tetragonal, often with pyramids). ## Crystal Forms Chabazite-Ca crystallizes in the trigonal system, but its crystals are almost always rhombohedra with angles close to 90°, giving them a cubic appearance. Twinning is very common, especially simple and penetration twins, where crystals appear to interpenetrate each other. It occurs as single crystals, crystal groups, and druses lining the interiors of geodes and fissures.

Geological environment

## Genesis Chabazite-Ca is a typical low-temperature hydrothermal mineral. It forms as a result of the activity of post-magmatic waters or circulating waters in the Earth's crust, which react with volcanic rocks, especially basalts and andesites. It crystallizes in cavities, gas vesicles (amygdules), and fissures of these rocks, filling them with secondary minerals. It can also form in volcanic tuffs that have undergone alteration in contact with groundwater or saline lakes. ## Mineral Associations As a mineral from the zeolite group, Chabazite-Ca often co-occurs with other members of this group, such as heulandite, stilbite, analcime, as well as with calcite, quartz (including chalcedony and agate), and apophyllite. ## Localities Chabazite-Ca is a widely distributed mineral worldwide. Classic, historical localities include Fassatal (Val di Fassa) in Italy, Oberstein in Germany, and the Faroe Islands. Beautiful, orange specimens come from Two-Up, Rose Creek, and other locations in Grant County, Oregon (USA). In Canada, it is known from the Bay of Fundy region in Nova Scotia (famous specimens from Wasson's Bluff). Other important localities include the areas around Pune and Nashik in India (in Deccan Traps basalts), Iceland, and some locations in Australia (Victoria).

Rarity

Common

For collectors

## Quality Criteria Specimens with large, sharp, well-formed crystals with strong luster are most valued by collectors. Crystals with intense coloration (e.g., orange, salmon) or perfectly colorless and transparent are particularly sought after. The aesthetic arrangement of crystals on a contrasting rock matrix, as well as the presence of penetration twins, enhances a specimen's attractiveness. Specimens without mechanical damage, with complete crystals, fetch the highest prices. ## Popular Localities Specimens from the Bay of Fundy region in Nova Scotia (Canada), especially from Wasson's Bluff, where beautiful, pinkish-orange crystals on basalt were found, are considered classic and among the best in the world. High-quality orange chabazites also come from Oregon, USA. Indian localities around Pune and Nashik provide large quantities of specimens with white or colorless crystals, often in association with other zeolites. Historical, though less productive today, are European localities such as Val di Fassa in Italy or the Faroe Islands.

Care and storage

## Cleaning Chabazite specimens are best cleaned mechanically using a soft, dry brush to remove dust and loose contaminants. If necessary, compressed air can be used. If washing is required, use only distilled water, applied gently. Avoid prolonged soaking, as it is a zeolite and can interact with water. ## What to Avoid Absolutely avoid contact with acids and other chemicals, which can damage or completely dissolve the mineral. Chabazite is sensitive to heat; heating leads to the loss of structural water (dehydration), causing it to dull and degrade. Do not expose specimens to prolonged strong sunlight or store them in humid conditions, which can promote undesirable chemical reactions. ## Storage Chabazite specimens are brittle and relatively soft, so they should be stored in a way that protects them from impacts and scratches, preferably in separate boxes or on a soft surface. Avoid storing in places with large temperature and humidity fluctuations. Well-formed crystals on a rock matrix are particularly susceptible to mechanical damage.

External references

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