sedimentary

Chert pebble

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Dark grey to greenish-grey with dark fracture veins; Luster: Waxy to dull; Crystal structure: Microcrystalline; Conchoidal fracture pattern.

Hardness: 7 Mohs scale
Color: Dark grey to greenish-grey with dark fracture veins
Luster: Waxy to dull

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Dark grey to greenish-grey with dark fracture veins; Luster: Waxy to dull; Crystal structure: Microcrystalline; Conchoidal fracture pattern.

Formation & geological history

Forms through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments. This specimen has been rounded by fluvial or marine water action.

Uses & applications

Historically used for stone tools due to its sharp edges when broken; used today in landscaping, construction aggregate, and as a material for lapidary tumbling.

Geological facts

Chert is so hard it can scratch glass. It was one of the first materials used by early humans to create arrowheads and scrapers. The dark lines are often secondary silica-filled fractures or manganese dendrites.

Field identification & locations

Identify in the field by its extreme hardness, smooth waxy texture, and conchoidal (shell-like) fracture surfaces. Commonly found in riverbeds and on beaches.