sedimentary

Quartz Geode

Silicon Dioxide (SiO2) within a secondary sedimentary structure

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Clear to white internal crystals with a brownish-gray outer shell; Luster: Vitreous (glassy) crystals; Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Luster: Vitreous (glassy) crystals

Identified March 21, 2026More sedimentary →

Explore Quartz Geode in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the precipitation of minerals from hydrothermal fluids or groundwater within cavities of sedimentary rocks (like limestone) or volcanic ash. These cavities are often created by gas bubbles or decomposed organic matter. They can date from millions to hundreds of millions of years old.

Uses & applications

Primarily used for geological education, home decor, and mineral collecting. Large-scale quartz is used in industry for electronics (piezoelectric properties) and glassmaking, though geodes are mainly aesthetic specimens.

Geological facts

Geodes are often referred to as 'thunder eggs' in certain regions. While they look like ordinary round rocks on the outside, they are hollow and lined with crystals. The largest geode ever found is the 'Empress of Uruguay,' which stands over 11 feet tall.

Field identification & locations

Identify in the field by looking for rounded, nodular rocks that feel lighter than they look (indicating a hollow center). Common locations include the Keokuk region (Iowa/Illinois/Missouri), Morocco, Brazil, and Mexico. For collectors, look for intact shells with well-defined, sparkling crystals.