sedimentary

Chert (Yellow/Tan variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, yellow-brown, or butterscotch; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Tan, yellow-brown, or butterscotch
Luster: Waxy to dull

Identified February 13, 2026More sedimentary →

Explore Chert (Yellow/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 (Mohs scale); Color: Tan, yellow-brown, or butterscotch; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the precipitation of silica from groundwater or within deep-sea marine environments where silica-rich organisms (like radiolarians) accumulate and recrystallize. Often found in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include road construction aggregate and decorative garden stones.

Geological facts

Chert is so hard it can create sparks when struck against steel, which made it a critical material for 'flintlock' firearms and ancient fire-starting techniques.

Field identification & locations

Identify in the field by its smooth, waxy texture and characteristic 'shell-like' (conchoidal) curved breaks. It cannot be scratched by a steel knife. Commonly found in riverbeds and eroded limestone outcrops.