sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and brownish-red; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and brownish-red
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and brownish-red; 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 the chemical replacement of limestone/dolomite. This specimen likely originates from Paleozoic or Mesozoic sedimentary beds.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; modernly used as road aggregate, decorative landscaping, and occasionally lapidary work for jewelry.
Geological facts
Chert is so durable that it often survives as 'river pebbles' long after the surrounding rock has eroded. It was the primary material for 'flint' fire-starting tools in ancient civilizations.
Field identification & locations
Identify in the field by its smooth, waxy surface and its ability to scratch glass. It breaks with sharp, curved 'shell-like' edges. Very common in stream beds and gravel pits worldwide.
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