sedimentary

Geode with Quartz and Chalcedony

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brownish-grey weathering, clear to white interior crystals; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: Approx 2.65

Hardness: 7 (Mohs scale)
Luster: Vitreous (glassy) inside, dull/earthy outside

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich hydrothermal fluids or groundwater within cavities of host rocks (likely limestone or volcanic ash). Over thousands of years, layers of chalcedony form the shell, followed by macro-crystalline quartz centers.

Uses & applications

Primarily used for geological collecting, decorative display, and metaphysical 'crystal' markets. Highly translucent specimens may be cut into cabochons for jewelry.

Geological facts

Geodes are often 'biological timers' or 'chemical capsules' that can remain unchanged for millions of years while the surrounding rock erodes away. This specimen shows a botryoidal (grape-like) chalcedony growth common in sedimentary environments.

Field identification & locations

Identify in the field by looking for rounded, knobby nodules that feel lighter than they look (indicating a hollow center). Commonly found in the Midwestern United States (Keokuk region) and desert regions of the Southwest. Use a rock hammer to carefully crack or a lapidary saw to reveal the interior.