sedimentary

Geode (unopened)

Silica-filled Concretion (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (outer shell/internal quartz). Color: Tan, brown, or grayish exterior with pitted 'cauliflower' texture. Luster: Dull/earthy exterior. Structure: Spherical or subspherical nodules.

Hardness: 7 (outer shell/internal quartz)
Luster: Dull/earthy exterior

Identified May 3, 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 (outer shell/internal quartz). Color: Tan, brown, or grayish exterior with pitted 'cauliflower' texture. Luster: Dull/earthy exterior. Structure: Spherical or subspherical nodules.

Formation & geological history

Formed in sedimentary rock cavities (like limestone) or volcanic ash. Over millions of years, mineral-rich groundwater seeps into hollow spaces, depositing layers of silica or calcite. These specific 'mudball' types are common in Paleozoic sedimentary layers.

Uses & applications

Primarily for geological collecting, education, and interior decoration once cut and polished. High-quality specimens with amethyst or agate centers are used in jewelry.

Geological facts

The word geode comes from the Greek word 'Geoides' meaning earth-like. Many geodes are millions of years old and remain hollow inside until someone cracks them open.

Field identification & locations

Identify by its rounded, uneven 'cauliflower' exterior and surprising lightness compared to solid rocks. Found globally, but famous in the US Midwest (Keokuk) and Brazil.