sedimentary

Chert (Chalcedony/Agate variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish; Luster: Waxy to vitreous; Crystal structure: Hexagonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, or grayish
Luster: Waxy to vitreous

Identified April 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids in sedimentary basins or by the replacement of limestone. Can occur as nodules or bedded deposits. Geologically, these can range from Precambrian to Holocene.

Uses & applications

Used historically for stone tools due to its sharp edges; used today as decorative stones, gemstones (agates), and in high-quality abrasive materials.

Geological facts

Ancient humans used chert for thousands of years to create arrowheads, scrapers, and knives because it breaks with a conchoidal fracture, creating razor-sharp edges.

Field identification & locations

Identify in the field by its waxy appearance and shell-like (conchoidal) breaking pattern. It is commonly found in limestone deserts or riverbeds. It is hard enough to scratch glass.