A white mineral consisting of silica; found in volcanic rocks WordNet 3.0 & Open English WordNet

Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. Wikipedia

Silica mineral, polymorph of quartz Wikidata

A mineral of volcanic rocks that solidified at a high temperature. Cristobalite is chemically identical to quartz, with the chemical formula SiO2, but has a different crystal structure. Crystals are always microscopic, and usually form small rounded masses. Wiktionary

Mineral. Wiktionary (translation)