sedimentary

Tumbled dark chert or jasper

Microcrystalline quartz (SiO₂), likely iron-stained chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray-brown with reddish-brown patches, dull to waxy luster, very fine-grained and massive, with no visible cleavage. The rounded shape indicates natural abrasion or tumbling.

Identified September 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills sediment, producing cryptocrystalline quartz; red-brown areas commonly reflect iron oxides. Chert ranges from Precambrian to modern and occurs in many sedimentary environments.

Uses & applications

Used for flint tools, aggregate, landscaping, and decorative tumbled stones; attractive jasper varieties are used in cabochons and carvings.

Geological facts

Chert can fracture with sharp conchoidal edges and may resemble dark jasper, flint, or weathered volcanic rock. The image alone cannot reliably distinguish among these varieties.

Field identification & locations

Identify by its glassy-to-waxy surface, very fine texture, lack of cleavage, and ability to scratch ordinary glass; it should not fizz in dilute hydrochloric acid. Common worldwide, especially in limestone, chalk, and volcanic-sedimentary terrains.