sedimentary

Geode (Unopened)

Silica-lined Vug (primarily SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (exterior shell, typically chalcedony/chert); Color: Tan, white, or gray exterior; Luster: Dull/earthy exterior; Structure: Spherical to subspherical nodule; Specific Gravity: ~2.6-2.65

Hardness: 7 (exterior shell, typically chalcedony/chert)
Color: Tan, white, or gray exterior
Luster: Dull/earthy exterior

Identified February 22, 2026More sedimentary →

Explore Geode (Unopened) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (exterior shell, typically chalcedony/chert); Color: Tan, white, or gray exterior; Luster: Dull/earthy exterior; Structure: Spherical to subspherical nodule; Specific Gravity: ~2.6-2.65

Formation & geological history

Formed as hollow cavities in sedimentary rock (like limestone) or volcanic ash. Over millions of years, mineral-rich groundwater seeps into the cavity, depositing layers of crystals (usually quartz or calcite) on the interior walls. Age varies from 10 to 250+ million years depending on the host formation.

Uses & applications

Primarily used as decorative specimens for collectors, educational tools in geology, and occasionally cut into bookends or jewelry (druzy quartz).

Geological facts

Geodes are often described as 'geological surprise eggs' because their internal beauty is hidden until they are cracked open. The largest geode ever found is the 'Crystal Cave' in Ohio, measuring 35 feet in diameter.

Field identification & locations

Identify in the field by looking for unusually round, lumpy rocks that feel lighter than they look (if hollow). Common in desert regions or limestone beds. Collectors look for 'rattlers' where loose crystals can be heard inside.