sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: tan to grayish-green with a matte to waxy luster, Shell-like (conchoidal) fracture, dense cryptocrystalline texture, no visible grains.

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan to grayish-green with a matte to waxy luster, Shell-like (conchoidal) fracture, dense cryptocrystalline texture, no visible grains.

Formation & geological history

Formed by the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins; commonly found as nodules or layers within limestone and basalt formations.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers); currently used as a grinding media in ball mills and as decorative gravel or road fill.

Geological facts

This specimen displays classic conchoidal fracture patterns typical of silica-rich rocks; flint is a high-quality variety of chert. The Pacific Northwest, where this specimen was found, has extensive deposits of chert associated with oceanic basalt accretions.

Field identification & locations

Identify in the field by its hardness (it should scratch glass) and its sharp, jagged edges when broken. It is extremely common in the Columbia River Gorge region near the user's location.