sedimentary

Chert (varietal: Jasper or Flint)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish with dark inclusions; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, brown, or grayish with dark inclusions
Luster: Dull to waxy

Identified March 4, 2026More sedimentary →

Explore Chert (varietal: Jasper or Flint) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in groundwater. These specimens can range from hundreds of millions to billions of years old, often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, jewelry (tumbled stones), and as a decorative landscaping rock.

Geological facts

Chert was one of the most vital materials for early humans because its conchoidal fracture allows it to be 'knapped' into razor-sharp arrowheads and scrapers. Depending on impurities, it is known as Jasper (red/brown), Flint (dark gray/black), or Agate (banded).

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial tills, and sedimentary rock outcrops.