sedimentary
Chert Pebble (Flint)
Microcrystalline/Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray to olive with white inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray to olive with white inclusions
- 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: Gray to olive with white inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the accumulation of silica-rich organic debris (like radiolarians or diatoms) within sedimentary beds. This specimen has been rounded by fluvial (river) or coastal erosion during the Holocene epoch.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include road ballast, decorative landscaping gravel, and as a raw material for fire-starting in survival kits.
Geological facts
When struck against steel, chert produces sparks, making it essential for flintlock firearms and early fire-making. It is one of the most durable common rocks, often surviving long-distance transport in rivers and along shorelines.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth texture, and white weathered 'cortex' or patches. Commonly found in riverbeds, glacial tills, and beaches worldwide. This specific specimen shows characteristic rounding and impact scars from water transport.
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