sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, brown with orange/yellow iron staining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, brown with orange/yellow iron staining
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a chemical precipitate or through the replacement of limestone. This specimen appears to be a rounded river-worn cobble, often found in ancient glacial or fluvial deposits. Age can range from Precambrian to Cenozoic depending on the bedrock source.

Uses & applications

Historical use for stone tools/arrowheads due to conchoidal fracture. Modern uses include aggregate for road construction, landscaping, and decorative tumble stones for collectors.

Geological facts

Chert is a tough, durable rock that often survives long-distance transport by rivers where softer rocks break down. In antiquity, high-quality cher (flint) was the primary material for the world's first industrial-scale mining operations.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy luster, and its characteristic curved, shell-like (conchoidal) fractures. Found globally in creek beds, gravel pits, and sedimentary outcrops.

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