sedimentary

Chert (Yellow or Tan variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, yellow, or light brown
Luster: Waxy to dull

Identified March 29, 2026More sedimentary →

Explore Chert (Yellow or Tan variety) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of silica-rich micro-organisms (like radiolarians or diatoms) on the ocean floor or through chemical precipitation in groundwater. It can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modernly used in road construction as aggregate, in decorative landscaping, and occasionally as semi-precious gemstones (jaspers).

Geological facts

Chert is so durable that it often remains behind as 'residual soil' after the surrounding limestone or more soluble rocks have weathered away. It was one of the most vital resources for prehistoric humans to create arrowheads and scrapers.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture patterns, extreme hardness (it will scratch glass and steel), and smooth, waxy texture. Commonly found as nodules or layers within limestone or dolomite beds.