sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray-blue with orange/red iron oxide staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray-blue with orange/red iron oxide staining
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or from chemical precipitation. The iron staining occurs when the rock is exposed to oxygen and water over geological time.

Uses & applications

Used historically for stone tools (knapping) due to its sharp edges; modern uses include road ballast, decorative landscaping, and occasionally lapidary work for jewelry.

Geological facts

Chert is so durable that it is often found as 'float' in stream beds long after the surrounding limestone has eroded away. Prehistoric humans specifically sought this material for spearheads and flintknapping.

Field identification & locations

Identify in the field by its characteristic smooth, shell-like (conchoidal) fracture and its ability to scratch glass. It often occurs as nodules within limestone or chalk beds.