sedimentary

Quartz-lined Geode / Chalcedony Nodule

Silicon Dioxide (SiO2)

Hardness of 7 on the Mohs scale, colors range from white, gray, and brown on the exterior to sparkling clear or white quartz crystals inside, vitreous luster on crystal faces, trigonal crystal system, conchoidal fracture with no true cleavage, specific gravity of 2.65.

Identified August 6, 2026More sedimentary →

Explore Quartz-lined Geode / Chalcedony Nodule in the encyclopedia →

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Physical properties

Formation & geological history

Formed in cavities or vesicles within sedimentary or volcanic rocks where silica-rich groundwater percolated through, slowly depositing microscopic quartz crystals over millions of years.

Uses & applications

Used primarily as decorative ornamental specimens, mineral collecting, lapidary arts, and sometimes in jewelry making.

Geological facts

Geodes form when dissolved minerals seep into a hollow cavity in a rock and crystallize along the inner walls over thousands to millions of years. The exterior host rock often weathers away faster than the quartz interior, leaving durable geode nodules behind.

Field identification & locations

Can be identified in the field by its nodular, rounded shape, relatively heavy weight for its size, and the distinctive hollow cavities lined with tiny sparkly crystals when cracked open. Frequently found in limestone formations.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

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Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary