sedimentary

Chert (Chalcedony/Agate)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Honey-yellow to orange-brown (due to iron oxides); Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.

Hardness: 7 on Mohs scale
Color: Honey-yellow to orange-brown (due to iron oxides)
Luster: Waxy to vitreous

Identified June 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater or within sedimentary rock layers, often replacing original mineral material or filling cavities. It can range from millions to hundreds of millions of years old.

Uses & applications

Historically used for making stone tools; currently used for lapidary work, jewelry (as agate/carnelian), and as decorative gravel.

Geological facts

This specimen displays a classic conchoidal fracture (shell-like curves), which is why similar materials like flint were prized by prehistoric humans for making sharp arrowheads and knives.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and the way it breaks into sharp, curved edges. Commonly found in riverbeds or within limestone formations.