sedimentary

Chert (and Limestone Pebbles)

Silicon Dioxide (SiO2) / Sedimentary Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: White, tan, brown, grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: White, tan, brown, grey
Luster: Waxy to dull

Identified June 11, 2026More sedimentary →

Explore Chert (and Limestone Pebbles) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 Mohs; Color: White, tan, brown, grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms) or chemical precipitation from groundwater within limestone/chalk beds. These specimens are fluvially worn river stones.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to conchoidal fracturing. Modernly used in construction aggregate, landscaping, and flint-making for fire starting.

Geological facts

Chert is so durable that it often remains as pebbles in riverbeds long after the surrounding limestone host rock has eroded away. The specimen in the center shows 'vugs' or pits where softer minerals have weathered out.

Field identification & locations

Identify by its hardness (scratches glass), waxy appearance, and smooth rounded shape in river deposits. Common globally in areas with ancient seafloor sedimentary deposits.