sedimentary

Chert (with Quartz vein/coating)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray with white/cream mineral coating; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray with white/cream mineral coating
Luster: Dull to waxy

Identified April 11, 2026More sedimentary →

Explore Chert (with Quartz vein/coating) 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 on Mohs scale; Color: Gray with white/cream mineral coating; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. The white veins are typically secondary quartz or calcite precipitated from groundwater in cracks.

Uses & applications

Historically used for making stone tools (arrowheads) due to conchoidal fracturing. Modernly used as construction aggregate, road surfacing, or as a decorative landscaping stone.

Geological facts

Chert is so hard it can strike sparks against steel. It is one of the most common materials used by prehistoric humans for tool-making worldwide.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel pocket knife) and the way it breaks into smooth, curved surfaces. Commonly found in limestone beds or as rounded pebbles in riverbeds and beaches.