sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and dark grey mottling. Luster: Dull to waxy. Crystal Structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brown, tan, and dark grey mottling
- 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 on Mohs scale. Color: Brown, tan, and dark grey mottling. Luster: Dull to waxy. Crystal Structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary beds, typically in marine environments. Age ranges from Precambrian to Recent.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in jewelry (lapidary), as a road aggregate, and for landscaping.
Geological facts
Chert has a conchoidal fracture which creates sharp edges, making it the primary material for prehistoric tool making. It is often found as nodules inside limestone or chalk beds.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture pattern. Common in riverbeds and limestone outcrops globally.
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