sedimentary

Chert (Agatized/Chalcedony variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale); Color: Tans, grays, and whites; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.

Hardness: 6
Color: Tans, grays, and whites
Luster: Waxy to vitreous

Identified April 8, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 (Mohs scale); Color: Tans, grays, and whites; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.

Formation & geological history

Formed through the precipitation of silica-rich fluids within sedimentary rock cavities or by the replacement of calcium carbonate. This chemical sedimentary rock usually originates in marine environments or volcanic ash deposits.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used in semi-precious jewelry (when polished), lapidary art, and as decorative gravel.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is often found as nodules inside limestone or chalk formations. If it exhibits concentric banding, it is specifically referred to as Agate.

Field identification & locations

Identify in the field by its smooth, waxy surface and conchoidal (shell-like) fracture patterns. It is extremely hard and will scratch glass. Commonly found along riverbeds, beaches, and limestone outcrops.