sedimentary

Chert / Flint

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, beige, or cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, beige, or cream
Luster: Waxy to dull

Identified March 12, 2026More sedimentary →

Explore Chert / Flint 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, beige, or cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds. Typically found in Paleozoic or Mesozoic age strata.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road surfacing, architectural stone, and as a component in ceramics.

Geological facts

Chert is so hard it can strike sparks from steel, which led to its extensive use in flintlock firearms. The specimen in the image shows distinct conchoidal (shell-like) fracturing on the edges, which is a hallmark of high-silica stones.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and metal), smooth waxy feel, and glass-like curved fractures. Commonly found as nodules or layers within sedimentary basins globally.