sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and creamy white cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Variegated brown, tan, and creamy white cortex
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and creamy white cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools/weapons (knapping) and fire-starting. Industrially used in construction aggregates; aesthetically used for lapidary work, cabochons, and decorative landscaping.
Geological facts
Chert was one of the most vital materials for early humans due to its ability to fracture into razor-sharp edges. It is extremely resistant to chemical weathering, which is why it often remains as 'river rocks' long after the surrounding limestone has eroded.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in riverbeds, glacial tills, and chalk cliffs. Collectors look for unique color patterns and translucency.
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