Chabazite-Na

Chemical formula: (Na<sub>3</sub>K)Al<sub>4</sub>Si<sub>8</sub>O<sub>24</sub>·11H<sub>2</sub>O

A silicate from the zeolite group, the sodium end-member of the chabazite series, forming characteristic pseudoregular, rhombohedral crystals.

## Characteristics Chabazite-Na is a hydrated aluminosilicate of sodium, potassium, and calcium, belonging to the zeolite group. It is the sodium analogue in the chabazite series. It forms rhombohedral crystals that are often so flattened they resemble cubes—hence the term "pseudoregular." The most characteristic feature of chabazite is penetration twinning, where two or more crystals appear to interpenetrate each other. It typically occurs as single crystals or groups of crystals growing on the walls of rock cavities. ## Physical Properties This mineral is characterized by a hardness of 4-5 on the Mohs scale, making it relatively soft. It has a vitreous luster and is transparent to translucent. Its density is approximately 2.08-2.1 g/cm³, making it a light mineral. It exhibits good cleavage parallel to the rhombohedron faces. ## Colors and Varieties Chabazite-Na is most often colorless or white. It can also be colored in yellowish, pink, salmon, or reddish-brown hues, which is a result of impurities. There are no named commercial varieties, and specimens are classified mainly based on color and form. ## History and Name The name "chabazite" comes from the Greek word *chabazios*, one of the stones mentioned in the ancient poem of Orpheus, and was given in 1792 by Bosc d'Antic. The suffix "-Na" was added later by the International Mineralogical Association (IMA) in 1997 to distinguish the sodium member of the series from its counterparts with dominant calcium (Chabazite-Ca), potassium (Chabazite-K), or strontium (Chabazite-Sr). ## Applications Chabazite-Na is primarily a valued collector's mineral. Zeolites as a group have wide industrial applications (e.g., as molecular sieves, catalysts, water softeners), but natural chabazite is rarely exploited on a large scale for this purpose—synthetic zeolites with controlled properties are preferred.

Properties

Mohs hardness
4-5
Luster
Vitreous
Streak
White
Density
2.08-2.1
Cleavage
Good on {10-11}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Trigonal

Diagnostic features

## Identification The most important diagnostic feature of chabazite-Na is its characteristic, pseudoregular rhombohedral crystals, often occurring as penetration twins. Its occurrence in gas vesicles in volcanic rocks (amygdules) is also a strong indicator. It does not react with cold, dilute hydrochloric acid. ## Distinguishing from Similar Minerals Chabazite-Na can be confused with other minerals, especially in the form of small crystals: - **Calcite**: Reacts vigorously with hydrochloric acid. It also has excellent rhombohedral cleavage, which is often visible on fracture surfaces. - **Apophyllite**: Usually has a stronger, often pearly luster on some faces and forms crystals with a different habit (combinations of prisms, pyramids, and basal pinacoids). - **Analcime**: Forms crystals in the shape of trapezohedra (24-faced forms), not rhombohedra. - **Other chabazites (e.g., Chabazite-Ca)**: Visual distinction from other members of the chabazite series is impossible without advanced chemical analysis (e.g., EDS). ## Crystal Forms Simple rhombohedra, which deceptively resemble cubes, are most commonly found. Penetration twins are common. It also occurs as granular aggregates or crusts.

Geological environment

## Genesis Chabazite-Na crystallizes under low-temperature hydrothermal conditions. It most often forms as a secondary mineral, filling empty spaces (gas vesicles, called amygdules) in volcanic rocks such as basalts, andesites, phonolites, and volcanic tuffs. ## Mineral Associations It often co-occurs with other zeolites, such as heulandite, stilbite, thomsonite, analcime, and phillipsite. It is also accompanied by calcite, quartz, chalcedony, and clay minerals from the smectite group (e.g., saponite). ## Localities Significant localities for chabazite-Na worldwide include: - **Italy**: Areas around Vesuvius and Etna; San Giorgio di Corona in Liguria (type locality). - **USA**: Ritter in Oregon (known for sharp, salmon-colored crystals); near Horseshoe Dam in Arizona; Patterson in New Jersey. - **Germany**: In the Vogelsberg volcanics in Hesse and in the Palatinate. - **Czech Republic**: In the Ústí nad Labem region. - **Portugal**: On Faial Island in the Azores archipelago.

Rarity

Not very common

For collectors

## Quality Criteria The most highly prized chabazite-Na specimens are characterized by sharp, well-formed, and large crystals with a distinct luster. Spectacular penetration twins are particularly sought after. Intense, uniform color (e.g., salmon-pink) and the placement of crystals on a contrasting rock matrix enhance attractiveness. The specimen should be free from mechanical damage. ## Popular Localities Among the most famous localities yielding high-quality collector specimens are Ritter in Oregon (USA), known for sharp, pink crystals, and classic localities in Italy. Specimens from these places command higher prices and are prized additions to advanced systematic or regional mineral collections.

Care and storage

## Cleaning Chabazite specimens should be cleaned gently, using a soft brush (e.g., a toothbrush) and distilled water. Strong rubbing should be avoided. Ultrasonic cleaners are not recommended, as vibrations can cause cracks along cleavage planes. ## What to Avoid The mineral is sensitive to sudden temperature changes, which can lead to cracking or loss of structural water and dulling. Contact with acids and strong detergents should be avoided. Due to its relatively low hardness, it is susceptible to scratches and mechanical damage. ## Storage Collector specimens of chabazite are best stored in separate, padded boxes or display cases to protect them from dust and accidental impacts. Prolonged exposure to direct sunlight should be avoided.

External references

Sources

Read more