sedimentary

Chert / Flint

Chert (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, tan, and gray; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, tan, and gray
Luster: Waxy to dull

Identified April 19, 2026More sedimentary →

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: Brown, tan, and gray; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. This specimen appears weathered, likely found in a fluvial or glacial environment.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used as a gemstone (Jasper/Agate varieties), in road construction, and for abrasive grinding.

Geological facts

Chert is so hard it can scratch glass and steel. Due to its conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, scrapers, and knives.

Field identification & locations

Identify in the field by its extreme hardness, smooth waxy surface when broken, and sharp edges. This specimen shows 'rinded' weathering common in field-collected river rocks.