sedimentary
Chert (Field Stone)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dull gray-green/brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Identified More sedimentary →
Explore Chert (Field Stone) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Dull gray-green/brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in saltwater environments. It is a dense, hard rock found in many geological ages from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (knapping); modernly used as road base, construction aggregate, and occasionally in lapidary work if highly colorful (e.g., Jasper).
Geological facts
Chert is so hard it can produce sparks when struck against steel, leading to its frequent use in flintlock firearms. This specific piece shows signs of natural weathering and a possible conchoidal fracture pattern.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture surfaces. Frequently found in limestone or chalk beds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary