sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or yellowish-brown
- Luster
- Waxy to dull
Identified More sedimentary →
Explore Chert (Jasper/Chalcedony) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation in sedimentary basins. It often replaces original carbonate materials in limestone.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregate and as a semi-precious gemstone in jewelry when it exhibits unique colors.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces razor-sharp edges. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules in limestone or as smooth river pebbles.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary