sedimentary
Chert (Flint Pebbles)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or gray with a dull to waxy luster; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or gray with a dull to waxy luster
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or gray with a dull to waxy luster; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed as nodules in limestone or chalk beds from the precipitation of silica. This specific specimen shows signs of alluvial weathering and water-tumbling, likely from a river or beach environment.
Uses & applications
Historically used for making stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as landscaping gravel.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for hunting and scraping.
Field identification & locations
Identify in the field by its smooth, rounded shape (if water-worn), extreme hardness, and distinctive shell-like (conchoidal) fracture pattern if broken. Commonly found in riverbeds and coastal areas.
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