sedimentary or igneous

Geode half

Geode (often quartz/chalcedony based)

Rough, weathered exterior; hollow interior often lined with crystals or chalcedony. Hardness varies depending on mineral lining (quartz is 7).

Identified August 3, 2026More sedimentary or igneous →

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Physical properties

Rough, weathered exterior; hollow interior often lined with crystals or chalcedony. Hardness varies depending on mineral lining (quartz is 7).

Formation & geological history

Formed in volcanic ash or sedimentary rock when a cavity is filled with mineral-rich groundwater, which deposits dissolved minerals on the inner walls over time.

Uses & applications

Commonly collected as specimens, used in decorative displays, or sometimes crafted into jewelry.

Geological facts

Geodes look like ordinary rocks on the outside but contain hollow cavities lined with crystals. They are popular among amateur rockhounds.

Field identification & locations

Identify by their relatively light weight for their size (due to being hollow) and rough, spherical or nodular exterior. Break or cut open to reveal the interior.

Other sedimentary or igneous specimens

See all

Pyrite

Iron Sulfide (FeS2)

mineral

Pebble (likely a type of sandstone or quartzite pebble)

Clastic Sediment (specifically, a rudite-sized clast). If the pebble is composed of a specific rock type, its scientific name would be that rock type (e.g., 'Quartzite pebble', 'Granite pebble', 'Chert pebble'). Given its appearance, it is likely a metamorphic quartzite pebble or a hard sandstone pebble.

Sedimentary rock

Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within Sedimentary or Igneous Matrix

igneous

Quartz Geode

Silicon Dioxide (SiO2) within Sedimentary or Igneous host

mineral

Quartz Geode

Silicon Dioxide (SiO2) within a sedimentary or igneous host

sedimentary

Geode (Unopened)

Quartz/Chalcedony concretion

sedimentary