sedimentary
Chert (Jasper/Opaline variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Dull greenish-yellow to tan; Luster: Waxy to vitreous; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 6
- Color
- Dull greenish-yellow to tan
- Luster
- Waxy to vitreous
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: Dull greenish-yellow to tan; Luster: Waxy to vitreous; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed from the accumulation of silica-rich microfossils or via chemical precipitation from silica-rich fluids in sedimentary basins or volcanic environments. Often associated with Cenozoic sedimentary layers.
Uses & applications
Historically used for stone tools due to its sharp edges; currently used for lapidary work, landscaping, and as a collector's specimen.
Geological facts
Chert is so hard that it can scratch glass and sparks when struck against steel. This specific waxy, greenish-tan appearance is often called common opal or jasper-chert depending on water content.
Field identification & locations
Identify in the field by its smooth, shell-like fracture (conchoidal) and extreme hardness. Commonly found in riverbeds, desert pavements, and exposed sedimentary outcrops across the Western United States.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
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
sedimentary