sedimentary

Quartzite / Chert Nodular Rock

Silicon Dioxide (SiO2) / Microcrystalline Quartz

Hardness 7 on the Mohs scale. Color ranges from light gray, off-white, to tan and brownish tones due to iron staining. Luster is dull to waxy/sub-vitreous. Conchoidal fracture lines and a fine-grained, massive crystal structure are visible.

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and precipitation of silica-rich fluids within sedimentary rock layers like limestone or chalk, or via chemical precipitation in marine environments over millions of years.

Uses & applications

Used historically by indigenous populations for knapping stone tools like arrowheads and scrapers. Modern uses include aggregate in construction, roadbed material, landscaping, and educational rock collecting.

Geological facts

Chert and quartzite specimens like this were essential materials for early human survival due to their ability to fracture predictably with sharp edges when struck.

Field identification & locations

Identified by its high hardness (scratches glass easily), waxy to dull surface texture, and smooth conchoidal fractures. Commonly found in riverbeds, limestone outcrops, and forested hilltops throughout North America and worldwide.

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