sedimentary

Quartz Geode

Quartz (SiO2) in a Sedimentary Vug

Hardness: 7 (Mohs scale), Color: tan to brown outer rind with clear/white internal crystals, Luster: Vitreous inner crystals/dull outer shell, Crystal Structure: Hexagonal (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified June 19, 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 as hollow cavities in sedimentary rocks (often limestone) or volcanic ash. Mineral-rich groundwater precipitates crystals over thousands of years inside the void. Most common in regions with Paleozoic or Mesozoic era deposits.

Uses & applications

Primarily used as decorative display pieces, for educational purposes in geology, and by collectors. Small geodes are sometimes used in jewelry as drusy pendants.

Geological facts

Geodes are essentially 'rocks with secrets'; a plain-looking exterior hides a hollow interior lined with sparkling crystals. The largest geodes in the world can be big enough for humans to step inside.

Field identification & locations

Identify in the field by looking for rounded, lumpy stones that feel unusually lightweight for their size. Common locations include Morocco, Brazil, and the Midwestern United States (Iowa/Illinois/Missouri).