mineral

Agate Geode

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5-7 on Mohs scale. Color: Translucent grey/blue with white banding and a crystalline center. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (trigonal). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Hardness: 6
Luster: Vitreous to waxy

Identified June 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic rock or sedimentary pockets. Siliceous fluids seep into these cavities over millions of years, depositing layers of microcrystalline quartz along the walls and often growing macro-crystals in the center.

Uses & applications

Used primarily in lapidary arts, jewelry making, ornamental displays, and as healing stones in metaphysical practices. Industrial uses include precision pendulums and laboratory mortars and pestles due to hardness.

Geological facts

Agate geodes are known as 'Thunder Eggs' in certain volcanic regions of the Western United States. No two geodes are exactly alike, as the banding reflects the unique chemical shifts during its formation.

Field identification & locations

Identify in the field by looking for rounded, cauliflower-like exterior nodules that feel unexpectedly light for their size. Commonly found in Brazil, Uruguay, and the US (Oregon and Iowa).

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral