mineral

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale; Color: Clear to milky white; Luster: Vitreous (glassy); Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Clear to milky white
Luster: Vitreous (glassy)

Identified March 18, 2026More mineral →

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Physical properties

Hardness: 7 on the Mohs scale; Color: Clear to milky white; Luster: Vitreous (glassy); Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Geodes form in hollow cavities in volcanic or sedimentary rocks. Over millions of years, mineral-rich groundwater seeps into these cavities, depositing layers of silica that eventually crystallize into quartz. Most commercial geodes date from the Cretaceous to the Neogene period.

Uses & applications

Primarily used for geological education, home decor, and mineral collecting. Occasionally small high-quality pieces are used in lapidary work or wire-wrapped jewelry.

Geological facts

The word 'geode' comes from the Greek word 'geodes', meaning 'earth-like'. They are often found by looking for lumpy, potato-shaped rocks that feel lighter than they look because they are hollow inside.

Field identification & locations

Identify in the field by looking for rounded nodules in limestone or volcanic ash beds. To confirm, one must crack them open or saw them. Common locations include Brazil, Uruguay, and the Midwest USA (Keokuk geodes).