sedimentary

Banded chert (likely flint or jasperoid)

Microcrystalline quartz/chalcedony, SiO₂

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, opaque to slightly translucent, waxy to dull luster, and no visible cleavage; this specimen shows dark gray-blue bands with lighter quartz-rich veinlets and a weathered brown rind. Its fine-grained, conchoidal fracture is characteristic of chert.

Identified August 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or cements sediment, often as nodules or beds in limestone and other marine sediments; individual pieces may range from Paleozoic to younger ages depending on locality.

Uses & applications

Used historically for sharp tools and fire-starting, and today for carving, lapidary work, landscaping, and small collectible specimens; usually not gem-grade.

Geological facts

The curved banding and sharp edges can resemble obsidian, but chert is generally less glassy and commonly has a rough weathering cortex.

Field identification & locations

Identify it by testing for glass-scratching hardness, observing conchoidal fracture, and checking that it lacks obsidian’s uniform volcanic glass texture. Common worldwide, especially in limestone regions; exact locality is needed for a precise variety assignment.