Mineral / Sedimentary

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: White to clear (druzy quartz) with a tan/beige outer rind; Luster: Vitreous/glassy crystals with a dull limestone or chalcedony exterior; Crystal Structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White to clear (druzy quartz) with a tan/beige outer rind

Identified March 18, 2026More mineral / sedimentary →

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Physical properties

Formation & geological history

Formed when mineral-rich groundwater seeps into hollow cavities in sedimentary limestone or volcanic ash. Over millions of years, the minerals precipitate out of the water, growing inward. Most common specimens range from 30 to 250 million years old.

Uses & applications

Primarily used for decorative display, educational purposes, mineral collecting, and in spiritual/metaphysical practices. Occasionally larger specimens are sliced for high-end furniture inlay or coasters.

Geological facts

Geodes are often called 'thunder eggs' when they are completely solid. The word 'geode' comes from the Greek word 'Geoides' meaning 'earth-like.' While they look like ordinary rocks on the outside, their hollow centers can contain diverse mineral varieties including amethyst, citrine, or calcite.

Field identification & locations

Identify in the field by looking for rounded, cauliflower-like nodules that feel lighter than regular rocks of the same size. They are commonly found in desert regions, particularly in Morocco, Mexico, and the Midwestern United States (Iowa/Illinois). Collectors should listen for a hollow sound when tapping lightly.