sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7.0 (Mohs scale), Color: Variegated (gray core with yellow/red iron-stained cortex), Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
- Hardness
- 6
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7.0 (Mohs scale), Color: Variegated (gray core with yellow/red iron-stained cortex), Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments; the colors result from oxidation of iron minerals within the silica matrix.
Uses & applications
Historically used for stone tools and arrowheads; currently used in jewelry (cabochons), as an abrasive, and for ornamental rock collections.
Geological facts
This specimen displays a distinct weathering rind or oxidation zone where the iron minerals have reacted with water and air to change color from the gray core to red/yellow.
Field identification & locations
Identified by its extremely smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Commonly found in nodules within limestone or as river-worn pebbles.
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