sedimentary

Chert (Chalcedony/Common Opal)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Brown, tan, translucent
Luster: Waxy to vitreous

Identified May 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from groundwater or as a replacement of organic material or limestone. Found in nodules or layered beds in various sedimentary environments worldwide.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when fractured. Modern uses include abrasives, gravel, and minor lapidary use for jewelry ornaments.

Geological facts

Flint is a variety of chert. Because of its hardness and silica content, it was the primary material for 'fire-starting' technology and projectile points for thousands of years.

Field identification & locations

Identify by its characteristic waxy surface and conchoidal (shell-like) fracture patterns. It cannot be scratched by a steel knife. Common in riverbeds and limestone outcrops.