sedimentary
Rough Agate/Chert Nodules
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Reddish-orange, tan, and creamy white; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.60–2.65.
- Hardness
- 6
- Color
- Reddish-orange, tan, and creamy white
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Reddish-orange, tan, and creamy white; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.60–2.65.
Formation & geological history
Formed as secondary deposits where silica-rich groundwater fills cavities in igneous or sedimentary rocks. This specimen appears to be a river-worn or alluvial nodule, likely millions of years old, weathered from its primary host rock.
Uses & applications
Commonly used for lapidary work (tumbling, cabochons), internal decoration, and as a semi-precious gemstone in jewelry when cut and polished.
Geological facts
Agate and Chert are essentially the same material, but 'Agate' is usually reserved for translucent or banded specimens, while 'Chert' is opaque. These stones have been used since the Stone Age to make tools and spearheads due to their sharp conchoidal fracture.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass and steel), and smooth, rounded water-worn exterior. Found frequently in riverbeds or areas with volcanic soil.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary