sedimentary
Chert (Septarian or Banded Nodular Variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs scale; Color: Dark brown, tan, and creamy white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Dark brown, tan, and creamy white
- Luster
- Dull to waxy
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: Dark brown, tan, and creamy white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich fluids within sedimentary host rocks, often as nodules or replacement layers. These patterns can form through dehydration and mineral infilling during diagenesis.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracture. Modern uses include landscaping, or semi-precious lapidary work for unique patterns.
Geological facts
This specimen displays characteristics of Septarian nodules or jasper-like chert banding. Chert is so durable it can survive millions of years of weathering, often found in riverbeds long after the surrounding rock has eroded.
Field identification & locations
Identify by its hardness (it will scratch steel and glass) and the smooth, curved surfaces where it has broken. Commonly found in limestone or chalk beds globally.
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