sedimentary

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan to brown exterior, white/clear internal crystals; Luster: Dull/earthy exterior, vitreous (glassy) interior; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture.

Hardness: 7 on Mohs scale
Color: Tan to brown exterior, white/clear internal crystals
Luster: Dull/earthy exterior, vitreous (glassy) interior

Identified July 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as hollow nodules in sedimentary or volcanic rock. Over millions of years, mineral-rich groundwater seeps into the hollow cavity, depositing layers of silica that crystallize into quartz. This specimen appears to be a whole or partially cracked nodule.

Uses & applications

Primarily used for geological education, home decoration, lapidary art, and rock collecting. High-quality geodes are often sliced and polished into bookends or coasters.

Geological facts

The word geode comes from the Greek word 'Geoides' which means 'earth-like'. No two geodes are exactly alike, and you cannot be certain what minerals are inside until they are cracked open.

Field identification & locations

Identify by their rounded, lumpy, cauliflower-like exterior texture and lighter weight relative to solid rocks of the same size. Commonly found in desert regions, particularly in the Midwestern USA (Keokuk, IA), Morocco, and Brazil.