sedimentary

Quartz Geode

Silicon Dioxide (SiO2) in a concretion

Hardness: 7 on the Mohs scale; Color: White to translucent crystals with a tan or grey outer rind; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65

Hardness: 7 on the Mohs scale
Color: White to translucent crystals with a tan or grey outer rind
Luster: Vitreous (glassy) inside, dull/earthy outside

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary rocks like limestone or volcanic ash. Over millions of years, mineral-rich groundwater seeps into hollow cavities, slowly precipitating layers of crystals inward from the outer shell. Many are from the Paleozoic or Mesozoic eras.

Uses & applications

Primarily used for decorative purposes, crystal healing, educational specimens, and as collectibles for mineral enthusiasts.

Geological facts

Geodes are often referred to as 'thunder eggs' when they are solid or filled with agate. The word 'geode' comes from the Greek term 'geodes' which means 'earth-like,' referring to their round, unremarkable exterior.

Field identification & locations

Identify in the field by looking for rounded, lumpy nodules that feel lighter than solid rocks. They are frequently found in desert regions or limestone quarries. To collect, check riverbeds or areas with volcanic/limestone outcrops.

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