Mineral Guide · Mineral

Cristobalite

Cristobalite is a high-temperature polymorph of silica, important in volcanic rocks, silica-rich glass and the study of phase changes in quartz-group minerals.

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Crystal structure

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Mineral properties

Formula: SiO₂
Class: Oxides
Crystal system: Tetragonal
Typical colours: colourless, white, grey
Lustre: Vitreous
Hardness: 6.50-7.00
Specific gravity: 2.27-2.33
Crystal habit: Granular, Spherulitic, Twinning
Origin: silica-rich volcanic rocks, cavities in rhyolite and andesite, and high-temperature industrial or ceramic environments

Related varieties

What is Cristobalite?

Cristobalite is a high-temperature polymorph of silica, important in volcanic rocks, silica-rich glass and the study of phase changes in quartz-group minerals.

Mineralogy and structure

The reference formula is SiO₂. Cristobalite belongs to the oxides and has a tetragonal crystal system. Cristobalite is tetragonal at higher temperatures and transforms to a lower-symmetry form on cooling. It is a silica polymorph, so its structure differs from the trigonal structure of ordinary quartz.

Colour and appearance

Typical colours include colourless, white, grey. Crystal habit, lustre, transparency and matrix association are often as diagnostic as colour.

Formation and localities

Cristobalite forms in or is associated with silica-rich volcanic rocks, cavities in rhyolite and andesite, and high-temperature industrial or ceramic environments. Important documented localities include Mexico, the United States, Iceland and many volcanic regions.

Collecting and care

Cristobalite is best kept as a labelled collector or reference specimen. Protect fragile crystals from impact and prolonged humidity changes. Lead-, arsenic-, chromium- and cobalt-bearing minerals should not be cut, ground or used in jewellery.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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