Mineral Guide · Mineral

Heulandite-Ca

Heulandite-Ca is a calcium-dominant zeolite, commonly forming pearly tabular crystals and rosettes in cavities of volcanic rocks.

Interactive 3D structure

Crystal structure

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Mineral properties

Formula: (Ca,Na)₅-6Al₉Si₂₇-28O₇₂·nH₂O
Class: Silicates
Crystal system: Monoclinic
Typical colours: green, colourless, white, pink, peach
Lustre: Pearly, Vitreous
Hardness: 3.50-4.00
Specific gravity: 2.10-2.20
Crystal habit: Prismatic, Spherical, Tabular
Origin: basalt cavities, volcanic tuffs and low-temperature hydrothermal zeolite veins

What is Heulandite-Ca?

Heulandite-Ca is a calcium-dominant zeolite, commonly forming pearly tabular crystals and rosettes in cavities of volcanic rocks.

Mineralogy and structure

Reference formula: (Ca,Na)₅-₆Al₉Si₂₇-₂₈O₇₂·nH₂O. Heulandite-Ca belongs to the heulandite subgroup and has an open hydrated framework. The calcium-dominant label distinguishes it from related Na-, K- and Sr-dominant compositions. Heulandite-Ca belongs to the silicates and has a monoclinic crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 2.1–2.2.

Colour and appearance

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

Formation and localities

Heulandite-Ca forms in or is associated with basalt cavities, volcanic tuffs and low-temperature hydrothermal zeolite veins. Important documented localities include India, Iceland, Scotland, Italy, Canada and the United States.

Collecting and care

Keep away from heat and strong chemicals; support thin plates and rosettes during display.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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