sedimentary
Geode with Quartz and Chalcedony
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brownish-grey weathering, clear to white interior crystals; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: Approx 2.65
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous (glassy) inside, dull/earthy outside
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brownish-grey weathering, clear to white interior crystals; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: Approx 2.65
Formation & geological history
Formed through the precipitation of silica-rich hydrothermal fluids or groundwater within cavities of host rocks (likely limestone or volcanic ash). Over thousands of years, layers of chalcedony form the shell, followed by macro-crystalline quartz centers.
Uses & applications
Primarily used for geological collecting, decorative display, and metaphysical 'crystal' markets. Highly translucent specimens may be cut into cabochons for jewelry.
Geological facts
Geodes are often 'biological timers' or 'chemical capsules' that can remain unchanged for millions of years while the surrounding rock erodes away. This specimen shows a botryoidal (grape-like) chalcedony growth common in sedimentary environments.
Field identification & locations
Identify in the field by looking for rounded, knobby nodules that feel lighter than they look (indicating a hollow center). Commonly found in the Midwestern United States (Keokuk region) and desert regions of the Southwest. Use a rock hammer to carefully crack or a lapidary saw to reveal the interior.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary