sedimentary
Chert (Arrowhead Preform or Flake)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Variegated brown, grey, and ochre; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Variegated brown, grey, and ochre
- 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, grey, and ochre; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; 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 in sedimentary environments. This specimen shows signs of hydration or iron staining from secondary mineral deposition.
Uses & applications
Historically used for stone tools (lithics) due to its sharp conchoidal fracture. Today used as a collector's specimen or for lapidary work.
Geological facts
This piece appears to be a 'preform' or a lithic flake, meaning it may have been handled or shaped by early humans for the purpose of making a tool. Its tapered shape is classic for tool-making debris.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and shell-like (conchoidal) fractures. Common in riverbeds and limestone outcrops. Look for 'bulb of percussion' or ripple marks on the surface which indicate it was struck.
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