sedimentary
Geode (Chert or Quartz Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Off-white, tan, or grey exterior; Luster: Dull/earthy exterior, vitreous (glassy) interior; Structure: Microcrystalline or cryptocrystalline; Specific Gravity: Approx 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Off-white, tan, or grey exterior
- Luster
- Dull/earthy exterior, vitreous (glassy) interior
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: Off-white, tan, or grey exterior; Luster: Dull/earthy exterior, vitreous (glassy) interior; Structure: Microcrystalline or cryptocrystalline; Specific Gravity: Approx 2.65.
Formation & geological history
Formed through the chemical precipitation of silica-rich groundwater within cavities of sedimentary or volcanic host rock. Most sedimentary geodes form in limestone or shale over millions of years.
Uses & applications
Primarily used for lapidary work, home decor, educational collecting, and spiritual purposes.
Geological facts
Geodes are often referred to as 'thunder eggs' when formed in volcanic ash. While they look like ordinary rocks on the outside, they can contain hollow centers lined with sparkling crystals or colorful agate banding.
Field identification & locations
Identify in the field by their rounded or 'cauliflower' bumpy texture and lighter weight compared to solid rocks. They are common in the American Midwest (Keokuk region) and Southwest, as well as Brazil and Uruguay.
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