analcime

Analcime is a tectosilicate mineral in the zeolite group with the chemical formula NaAlSi2O6·H2O. It consists of a three‑dimensional framework of silicon and aluminum tetrahedra that creates channels containing sodium ions and water molecules. Analcime crystallizes in the isometric (cubic) system and commonly forms trapezohedral crystals that can resemble a truncated cube, though it also occurs as granular masses or rounded crystals.

Physically, analcime is typically colorless, white, or pale gray and exhibits a vitreous luster. It is usually transparent to translucent and has a Mohs hardness of about 5–5.5 with a specific gravity near 2.2–2.3. Because it belongs to the cubic system, analcime is optically isotropic.

Formation and occurrence: Analcime forms at low temperatures in hydrothermal environments and in alkaline, silica‑deficient volcanic rocks such as basalts, phonolites, and nephelinites. It commonly occurs in vesicles and fracture fills and is frequently found alongside other zeolites, including natrolite, stilbite, and chabazite. It is widely reported in volcanic rocks and in alteration zones where zeolite minerals precipitate from circulating fluids.

Distribution and significance: Analcime is found in many parts of the world, including basaltic and alkaline volcanic suites, as well as in hydrothermally altered rocks. While it has no major commercial use on its own, the zeolite group to which analcime belongs is of interest for ion exchange and adsorption properties, and the mineral is of interest to collectors and researchers studying zeolite assemblages and low-temperature mineralizing environments.

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