Mineral Guide · Mineral

Gmelinite

Gmelinite is a hydrated zeolite-group mineral with open framework channels, often forming pale hexagonal crystals or rounded aggregates.

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Crystal structure

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Mineral properties

Formula: (Na,Ca)₄Al₆Si₆O₂₄·6H₂O
Class: Silicates
Crystal system: Hexagonal
Typical colours: yellow, colourless, white, pink, orange
Lustre: Pearly, Vitreous
Hardness: 4.50-5.00
Specific gravity: 2.00-2.20
Crystal habit: Hexagonal, Spherical, Tabular
Origin: basalt cavities, volcanic tuffs and low-temperature alkaline hydrothermal environments

What is Gmelinite?

Gmelinite is a hydrated zeolite-group mineral with open framework channels, often forming pale hexagonal crystals or rounded aggregates.

Mineralogy and structure

Reference formula: (Na,Ca)₄Al₆Si₆O₂₄·₆H₂O. Gmelinite is compositionally variable and may be Na-, K- or Ca-dominant. The open zeolite framework contains exchangeable cations and water. Gmelinite belongs to the silicates and has a hexagonal crystal system. Typical hardness is 4.5–5 on the Mohs scale and specific gravity is approximately 2.0–2.2.

Colour and appearance

Typical colours include colourless, white, pink, yellow, orange. The usual hexagonal, tabular, spherical habit and vitreous, pearly lustre are useful descriptive features, but colour alone is not diagnostic.

Formation and localities

Gmelinite forms in or is associated with basalt cavities, volcanic tuffs and low-temperature alkaline hydrothermal environments. Important documented localities include Iceland, Ireland, India, Canada, the United States and New Zealand.

Collecting and care

Protect from heat, acids and impact because zeolite frameworks are hydrated and often delicate.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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