sedimentary

Tumbled jasper or chert pebble

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

AI-generated identification · may be incorrect

Opaque olive-brown to mustard-brown, waxy to dull luster, very fine-grained cryptocrystalline structure, and no visible cleavage; hardness about 6.5–7 Mohs, with conchoidal fracture. The rounded shape appears naturally water-worn or tumbled, and surface lines may be cracks or polish marks.

Identified August 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills sediment, producing microcrystalline quartz, with iron oxides creating the brown coloration. Such material commonly formed in sedimentary or volcanic environments over broad geologic timescales, often Paleozoic to younger.

Uses & applications

Used as inexpensive lapidary rough, cabochons, beads, carvings, and decorative tumbled stones; rarely used as aggregate or ornamental stone. Typical collector value is modest.

Geological facts

Jasper is an opaque variety of chert, whereas chert may be translucent or more uniformly gray; the boundary is often informal. Its distinctive conchoidal fracture and resistance to scratching help separate it from softer brown rocks.

Field identification & locations

Common in gravel beds and silica-rich formations worldwide, including the western United States, Australia, India, and Africa. Test with a steel file or quartz: genuine jasper/chert resists scratching, while a streak or fizzing reaction would suggest another material.