sedimentary

Tumbled brown chert or jasper pebble

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

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown to reddish-brown, opaque, waxy to dull luster, very fine-grained cryptocrystalline quartz with no visible cleavage. Its smoothly rounded surface indicates natural water wear or tumbling; dark patches may be manganese or iron staining.

Identified September 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or cements sediment, commonly in limestone, volcanic, or marine environments; iron oxides create the brown coloration. The specimen’s exact geological age cannot be determined from the photograph.

Uses & applications

Used for lapidary carvings, cabochons, beads, and decorative stones; chert is also historically important for sharp tools and fire-starting. Common material has modest commercial value.

Geological facts

Chert and jasper are varieties of microcrystalline quartz, and the boundary between the names is informal; jasper is typically more opaque and impurity-rich. A silica-rich composition makes it resistant to weathering and abrasion.

Field identification & locations

Common in gravel beds, river cobbles, sedimentary formations, and volcanic terrains worldwide; notable sources include the Great Lakes region, Oregon, Texas, and Australia. It should scratch ordinary glass but not be scratched by a steel knife, although surface coatings or look-alikes can affect testing.