sedimentary

Weathered chert or chalcedony nodule

Microcrystalline quartz (SiO₂), possibly silicified limestone or agate-like chalcedony

AI-generated identification · may be incorrect

Pale blue-gray to cream, opaque to slightly translucent, with waxy-to-dull luster and irregular conchoidal fractures; Mohs hardness about 6.5–7, no obvious cleavage, and specific gravity near 2.6. The rough, weathered surface obscures any banding or crystal structure.

Identified August 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica-rich groundwater replaced or filled cavities in sedimentary rock, followed by uplift and weathering; exact age cannot be determined from the photograph. Similar material occurs in marine limestones, volcanic cavities, and sedimentary gravel deposits.

Uses & applications

Used for flaked stone tools, ornamental carvings, cabochons, and lapidary pieces; this specimen appears primarily of collecting or teaching interest.

Geological facts

Chert and chalcedony are varieties of quartz made of microscopic quartz crystals. A steel file should barely scratch it, while it can scratch ordinary glass.

Field identification & locations

Test hardness and inspect a fresh edge for glassy conchoidal fracture; a white streak, lack of fizz in dilute hydrochloric acid, and translucency support silica rather than limestone. Common sources include Texas, Oregon, California, Turkey, and many sedimentary basins.