sedimentary
Chert (often called Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Grey, tan, or brown, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Identified More sedimentary →
Explore Chert (often called Flint) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Grey, tan, or brown, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or chemical precipitation from silica-rich groundwater within other sedimentary rocks like limestone.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used today as road gravel, in concrete, and historically as the strike for flintlock firearms.
Geological facts
Because of its conchoidal fracture, it can be chipped to an edge only a few molecules thick, making it sharper than a steel scalpel. It is one of the most common materials used in the Stone Age.
Field identification & locations
Identify by its waxy luster, extreme hardness (it will scratch glass), and smooth, curved (conchoidal) breaks. Found worldwide, often as nodules within limestone or chalk beds.
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