Chabazite-Mg

Chemical formula: (Mg₀.₇K₀.₅Ca₀.₅Na₀.₁)Al₃Si₉O₂₄·₁₀H₂O

Chabazite-Mg is a rare mineral from the zeolite group, an hydrated magnesium, potassium, and calcium aluminosilicate, forming characteristic, almost cubic crystals.

## Characteristics Chabazite-Mg is a mineral belonging to the chabazite series within the zeolite group. As an hydrated aluminosilicate with magnesium as the dominant cation, it forms crystals with a characteristic, pseudorhombohedral or pseudocubic appearance. These crystals are often penetration twinned, which is a typical feature for minerals of this series. It usually occurs as well-formed, isolated crystals or groups of crystals grown on host rocks, often in gas vesicles in volcanic rocks. ## Physical Properties This mineral is characterized by a hardness of approximately 4.5 on the Mohs scale. It has a vitreous luster and is transparent to translucent. Its density is relatively low, typical for zeolites, and is about 2.11 g/cm³. ## Colors and Varieties Chabazite-Mg is most often colorless, white, or yellowish. No distinct color varieties or commercial varieties are distinguished; its name is defined by the dominance of magnesium in its chemical composition. ## History and Name The name "chabazite" comes from the Greek word *chabazios* (a type of stone), one of twenty stones mentioned in the poem "Peri lithos", attributed to Orpheus. The suffix "-Mg" was added in 1997 by the International Mineralogical Association (IMA) as part of a revision of zeolite nomenclature, to indicate that magnesium is the dominant extraframework cation in this particular mineral variety. Chabazite-Mg as a distinct species was formally recognized before 1997, and its type locality is Gobrein in Styria, Austria. ## Uses Chabazite-Mg, like other zeolites, has potential applications as a molecular sieve, catalyst, or in ion-exchange processes due to its porous crystalline structure. However, due to its rarity, it is primarily of scientific and collector's interest.

Properties

Mohs hardness: 4
Color: Colourless
Luster: Vitreous
Streak: White
Density: 1.98
Cleavage: Distinct/Good on {1011}
Fracture: Irregular/Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification The key diagnostic feature of Chabazite-Mg is its characteristic, pseudocubic or pseudorhombohedral crystals, often exhibiting penetration twinning. Occurrence in vesicles in volcanic rocks is also a strong indicator. Hardness (approximately 4.5) and vitreous luster aid in identification. ## Distinguishing from Similar Minerals Chabazite-Mg is visually indistinguishable from other minerals in the chabazite series (e.g., Chabazite-Ca, -Na, -K). Definitive differentiation requires advanced chemical analysis (e.g., EDS, WDS). It can be confused with other zeolites, such as analcime or phillipsite, but differs from them in crystal form. Calcite, often co-occurring, reacts with acid, which chabazite does not. ## Crystal Forms Crystals are trigonal, but their inter-facial angles are so close to 90° that they appear regular (cubic) or rhombohedral. They often occur as simple rhombohedra or combinations thereof. Penetration twinning, where two or more crystals interpenetrate each other, is very characteristic.

Geological environment

## Genesis Chabazite-Mg forms under low-temperature hydrothermal conditions. It most commonly crystallizes in vesicles and fractures in volcanic rocks, such as basalts, andesites, and phonolites, as a result of the alteration of volcanic glass by hydrothermal waters. It can also occur in volcanic tuffs that have been altered in saline lake environments. ## Mineral Associations This mineral often co-occurs with other zeolites, such as phillipsite, thomsonite, gmelinite, analcime, as well as with calcite, aragonite, and quartz (chalcedony). ## Localities The most important Chabazite-Mg localities worldwide include Gobrein in Styria (Austria - type locality), Weitendorf (Austria), some localities in the Czech Republic (near Ústí nad Labem), in Hungary, in Italy (e.g., near Vesuvius and Etna), and also in the United States (e.g., in Oregon and Arizona).

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with sharp, well-formed, and transparent crystals with a distinct luster. Large, isolated crystals or aesthetic groups on a contrasting rock matrix command higher value. Penetration twinning is a typical and desirable feature. Clarity (lack of inclusions) and absence of damage are crucial. ## Popular Localities Specimens from classic localities in Austria (Styria) and the Czech Republic are historically important. Attractive crystals have also been found in basalt vesicles in the Goble and Ritter area of Oregon, USA.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Allow the specimen to dry completely at room temperature. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral's structure. Chabazite-Mg is sensitive to high temperatures, which can cause water loss (dehydration) and crystal destruction. Do not clean it with ultrasonic or steam cleaners. ## Storage Chabazite-Mg specimens are brittle and relatively soft, so they should be stored in separate, padded boxes to prevent scratches and mechanical damage. Protect them from dust and sudden temperature changes.