sedimentary

Quartz Geode

Silicon Dioxide (SiO2) in a concretionary structure

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: tan to gray outer rind with white or clear crystalline interior, Luster: Vitreous/Glassy interior, dull exterior, Crystal Structure: Trigonal, Cleavage: None/Conchoidal fracture

Identified April 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the hollow precipitation of mineral matter within cavities or gas bubbles of volcanic or sedimentary rocks. Over millions of years, mineral-rich groundwater seeps into the cavity, depositing crystals layers. Most common geode-bearing layers range from 350 to 15 million years old.

Uses & applications

Primarily used for decorative display, educational purposes, mineral collecting, and metaphysical lapidary items. Small high-quality geodes are often cut for jewelry.

Geological facts

Geodes are derived from the Greek word 'Geoides' meaning 'earth-like'. While they look like ordinary round rocks on the outside, they contain hollow cavities lined with crystals. These specific specimens appear to be 'Keokuk geodes' or similar Moroccan varieties.

Field identification & locations

Identify in the field by looking for rounded, knobby concretions that feel lighter than typical rocks of the same size. They are often found in limestone or volcanic ash beds. Major locations include the Midwestern US (Iowa/Illinois), Mexico, Brazil, and Morocco.