sedimentary

Chert (Quartz Variety)

Chert (mostly SiO2 / Silicon Dioxide)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Creamy white to pale tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65

Hardness: 7 (Mohs scale)
Color: Creamy white to pale tan
Luster: Waxy to dull

Identified April 11, 2026More sedimentary →

Explore Chert (Quartz Variety) 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 (Mohs scale); Color: Creamy white to pale tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65

Formation & geological history

Forms primarily through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in limestone or chalk beds. This specimen appears weathered and water-worn, potentially from a riverbed environment.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Modernly used as road base, decorative landscaping rock, and occasionally for lapidary work.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is a dense, hard sedimentary rock that is chemically stable and very resistant to weathering.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy luster, and its characteristic curved, shell-like (conchoidal) fracture pattern when broken. It is commonly found in gravel pits and as nodules within limestone outcrops.