sedimentary
Chert (with Quartz Veining)
Microcrystalline silicon dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Dark grey to green-grey; Luster: Waxy to dull/earthy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Dark grey to green-grey
- Luster
- Waxy to dull/earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: Dark grey to green-grey; Luster: Waxy to dull/earthy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. This specimen shows secondary hydrothermal activity with quartz veining filling fractures.
Uses & applications
Historically used for stone tools (flintknapping). Today used as decorative stone, construction aggregate, and occasionally for folk medicine or in aquariums.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as 'firestone'.
Field identification & locations
Identify in the field by its extreme hardness, smooth waxy texture on fresh surfaces, and tendency to break like glass (conchoidal fracture). Common in limestone or dolostone formations.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary