sedimentary

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Off-white to tan exterior, typically white to clear crystals inside; Luster: Dull/earthy exterior, vitreous (glassy) interior; Crystal Structure: Hexagonal (Trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Luster: Dull/earthy exterior, vitreous (glassy) interior

Identified June 11, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed by the precipitation of mineral-rich water within hollow cavities of sedimentary or volcanic rocks. Over thousands of years, layers of silica crystals grow inward from the cavity walls. Common in limestone and shale beds of various geological ages.

Uses & applications

Primarily used as decorative display pieces, for geological education, and by lapidary hobbyists. They are also popular in metaphysical collections and as raw material for quartz extraction in some contexts.

Geological facts

Geodes are known as 'Thunder Eggs' in some cultures. While the exterior looks like an ordinary, lumpy rock, the interior can contain a hollow space lined with beautiful quartz or amethyst crystals. Some of the world's largest geodes are several feet in diameter.

Field identification & locations

Identify in the field by looking for round or oblong nodules with a distinctive cauliflower-like texture on the surface. They often feel lighter than solid rocks of the same size if they are hollow. Commonly found in desert regions or limestone-rich riverbeds.