sedimentary
Chert (Jasper)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Brown and dark tan patterns (muddy appearance), Luster: Waxy to dull, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 Mohs, Color: Brown and dark tan patterns (muddy appearance), Luster: Waxy to dull, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
Formation & geological history
Formed by the precipitation of silica from seawater or groundwater. This pebble was likely rounded by river or stream action, where silica replaced organic or sedimentary material over millions of years.
Uses & applications
Used for making stone tools (flintknapping) historically, landscaping, and in jewelry as a tumbled gemstone. High-quality patterned pieces are sought by lapidary hobbyists.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create sparks and sharp-edged tools due to its conchoidal fracture pattern. This specific specimen shows 'picture' or banded patterns typical of jasper varieties.
Field identification & locations
Identify by its hardness (will scratch glass) and smooth, waxy feel when wet. Often found in riverbeds, glacial tills, and sedimentary basins. Look for the characteristic curved break surfaces.
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