sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: tan, grey, beige with banding; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture; Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: tan, grey, beige with banding
Luster: waxy to dull

Identified June 13, 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: tan, grey, beige with banding; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture; Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich microfossils or precipitation from silica-rich groundwater within limestone or chalk beds. Often found as nodules or bedded layers.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include road surfacing materials, decorative landscaping, and as a raw material for silicon production.

Geological facts

Chert is so hard it can strike sparks against steel. High-quality colorful varieties are known as jasper or flint. It has been used by humans for over 2 million years.

Field identification & locations

Identify in the field by its extreme hardness (will scratch glass), waxy appearance, and sharp, shell-like edges when broken. Commonly found in limestone outcrops or riverbeds.