sedimentary

Chert (Jasper/Agate)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Dark grey with yellowish/tan inclusions (eye-like pattern). Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Dark grey with yellowish/tan inclusions (eye-like pattern)
Luster: Waxy to vitreous

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Dark grey with yellowish/tan inclusions (eye-like pattern). Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The smooth, rounded shape suggests it is a water-worn river stone or a tumbled specimen.

Uses & applications

Used for jewelry (cabochons), lapidary art, flintknapping (historically for tools), and as landscaping stone.

Geological facts

This specific piece is often called an 'eye stone' or 'orbital chert' due to the circular inclusion. Chert is extremely durable and was one of the primary materials used by prehistoric people for arrowheads.

Field identification & locations

Identify by its hardness (will scratch glass), smooth waxy feel, and characteristic shell-like (conchoidal) fractures. Often found in riverbeds, glacial till, or limestone outcrops.