sedimentary
Chert (Field Stone/Pebble)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to grayish-brown, Luster: dull to waxy, Crystal Structure: trigonal (micro), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to grayish-brown, Luster: dull to waxy, Crystal Structure: trigonal (micro), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. This specimen appears water-worn or weathered, likely found in a riverbed or glacial deposit.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road base, and as decorative gravel.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges. It is chemically identical to flint but usually lighter in color.
Field identification & locations
Identify by its ability to scratch glass and its smooth, shell-like fracture pattern. Common in sedimentary basins worldwide. This specific specimen is a tumbled river rock.
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