sedimentary
Quartz Geode with Chalcedony
Silicon Dioxide (SiO2) in Geode Form
Hardness: 7 (Mohs scale); Color: White, gray, tan; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, tan
- Luster
- Vitreous to waxy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, tan; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.65
Formation & geological history
Formed via secondary mineral precipitation in cavities of sedimentary limestone or volcanic ash. Ground water carries dissolved silica into hollow pockets where it cools or evaporates, leaving behind crystalline layers.
Uses & applications
Home decor, geological education, lapidary arts, and mineral collecting. Large, high-quality geodes are often used as statement décor pieces.
Geological facts
The word geode is derived from the Greek word 'Geoides' meaning earth-like. Unlike a vug, which is a cavity in rock, a geode is a self-contained structure that can be separated from its host rock.
Field identification & locations
Identify in the field by looking for rounded, pumpkin-like nodules that feel lighter than other rocks of the same size. Commonly found in desert regions or limestone beds in the Midwest US and Brazil.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary