sedimentary
Chert (also known as Flint or Common Chalcedony)
Cryptocrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and translucent grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (exhibits conchoidal fracture); Specific Gravity: 2.6 – 2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, white, and translucent grey
- 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: Tan, brown, white, and translucent grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (exhibits conchoidal fracture); Specific Gravity: 2.6 – 2.7.
Formation & geological history
Formed through the accumulation and chemical precipitation of silica-rich fluids within sedimentary rock layers, often replacing carbonate minerals or biological remains like shells and fossils. It can form as nodules or bedded layers in limestone or chalk through geological ages (Proterozoic to modern).
Uses & applications
Historically used for stone tools and arrowheads; used in construction for road base and concrete aggregate. High-quality specimens are used in jewelry (cabochons) or as decorative lapidary material.
Geological facts
Because it breaks with a conchoidal fracture (smooth, curved surfaces), flint was the primary resource for Stone Age technology. It is often found as smooth nodules inside chalk beds. It is chemically very resistant and often remains on the surface long after the surrounding limestone has weathered away.
Field identification & locations
Identify in the field by its high hardness (it will scratch glass and steel), waxy luster, and smooth, curved 'shell-like' chip marks (conchoidal fracture). It is common in riverbeds, glacial deposits, and sedimentary outcrops worldwide.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary