sedimentary
Chert (with Limestone/Carbonate matrix)
Sedimentary cryptocrystalline silica (SiO2)
Hardness: 6.5-7 Mohs scale; Color: Gray, tan, and yellowish-brown; Luster: Waxy to dull/earthy; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: approx. 2.65
- Hardness
- 6
- Color
- Gray, tan, and yellowish-brown
- Luster
- Waxy to dull/earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 Mohs scale; Color: Gray, tan, and yellowish-brown; Luster: Waxy to dull/earthy; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: approx. 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation within marine limestone beds. Common in Paleozoic and Mesozoic sedimentary basins.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used as road aggregate, in landscaping, and occasionally as a source of silica for industrial manufacturing.
Geological facts
Chert is so hard it can scratch glass and steel. High-quality varieties are known as flint. This specific specimen shows weathering rinds and potential secondary carbonate deposits.
Field identification & locations
Identify by its extreme hardness, waxy texture on fresh surfaces, and lack of visible grains. Often found as nodules or layers within limestone cliffs or in riverbeds after the softer limestone has eroded.
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