sedimentary

Quartz Geode

Crystalline Silicon Dioxide (SiO2) in Geode form

Hardness: 7 on Mohs scale; Color: Clear to milky white crystals with gray/brown outer shell; Luster: Vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Clear to milky white crystals with gray/brown outer shell
Luster: Vitreous

Identified May 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via chemical precipitation of mineral-rich groundwater within hollow cavities in sedimentary or volcanic rock. Over millions of years, silica layers deposit to form an outer chalcedony shell with internal crystal growth.

Uses & applications

Primarily used for geological education, home decor, and crystal collection. High-purity quartz is used in electronics and glass manufacturing.

Geological facts

Geodes are often called 'thunder eggs' and can remain hidden for millions of years looking like ordinary round rocks until they are cracked open to reveal their hidden hollow interior.

Field identification & locations

Identify in the field by looking for unusually light, round, or lumpy nodules in limestone or volcanic ash beds. A hollow sound when tapped is a key indicator. Commonly found in deserts like those in Morocco, Mexico, and the Western United States.

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