sedimentary
Chert (and Flint variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich biogenic material such as radiolarian or diatoms, or by chemical precipitation in groundwater replacing limestone/chalk. Found throughout Earth's history from Precambrian to modern times.
Uses & applications
Historically used for stone tools and starting fires (flint). Currently used in road surfacing, as an abrasive, and for decorative landscaping.
Geological facts
Chert was one of the first materials harvested by early humans to create arrowheads and scrapers due to its sharp edges when broken. 'Flint' is a dark variety of chert commonly found in chalk deposits.
Field identification & locations
Identify by its waxy appearance and shell-like (conchoidal) curves on broken faces. It will scratch glass easily. Commonly found as nodules or layers in limestone beds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary