sedimentary

Geode

Crystalline Quartz (SiO2) within a nodule

Hardness: 7 (Quartz center); Color: Tan/brown exterior with potential white, clear, or purple crystals inside; Luster: Dull/earthy exterior, vitreous (glassy) interior; Crystal structure: Trigonal/Hexagonal; Cleavage: None

Hardness: 7 (Quartz center)
Luster: Dull/earthy exterior, vitreous (glassy) interior

Identified June 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary or volcanic environments where hollow cavities are filled with mineral-rich hydrothermal fluids that slowly precipitate crystals over millions of years. Common in limestone and shale beds.

Uses & applications

Primarily used for geological education, tabletop decor, jewelry (ashlar or druzy), and as highly sought-after collector pieces.

Geological facts

The word geode comes from the Greek word 'Geoides' which means 'earth-like'. They may look like ordinary rocks on the outside but contain hollow centers filled with crystals.

Field identification & locations

Identified in the field by their rounded, bumpy, or 'cauliflower' exterior texture and their lighter weight compared to solid rocks of the same size. Commonly found in deserts or river beds in areas with volcanic or limestone history.