sedimentary
Chert (specifically Jasper/Flint pebble)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Opaque tan, brown, and ochre. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Opaque tan, brown, 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: 6.5-7 on Mohs scale. Color: Opaque tan, brown, and ochre. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary beds. This specimen is water-worn and likely from the Cenozoic era based on typical surface deposits.
Uses & applications
Historically used for stone tools and starting fires (striking against steel). Modernly used in landscaping, as tumbling rough for hobbyists, and in jewelry (as Jasper).
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges for arrowheads and scrapers. Different colors are caused by trace inclusions of iron oxides.
Field identification & locations
Identify in the field by its extreme hardness (will scratch glass) and waxy, smooth texture compared to other river rocks. Commonly found in riverbeds, gravel pits, and limestone formations.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary