sedimentary
Chert (Jasper/Flint variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Mottled brown, grey, and tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Mottled brown, grey, and tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Mottled brown, grey, and tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows significant rounding, indicating it was transported and weathered by water in a river or coastal environment over thousands of years.
Uses & applications
Historically used for stone tools and starting fires (striking steel). Modern uses include landscaping, jewelry (when polished), and as an abrasive in industrial applications.
Geological facts
Chert has been used by humans for over 2 million years to create sharp-edged tools like arrowheads and scrapers. Its ability to produce sparks when struck against iron or steel made it vital for survival until the invention of matches.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy feel, and characteristic 'clamshell' (conchoidal) chips or fractures. Usually found in riverbeds, gravel pits, or as nodules within limestone formations.
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