sedimentary
Chert (specifically Flint or Chalcedony nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to milky white with orange-brown weathering rind, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to milky white with orange-brown weathering rind, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation within limestone/chalk beds. Often found in Phanerozoic era strata.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used as road aggregate, in glass manufacturing, and as decorative landscaping stone.
Geological facts
Chert is so hard it can scratch steel and was the primary material for spearheads and arrowheads for thousands of years due to its predictable conchoidal fracturing which creates razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy interior against a rough, weathered outer 'cortex.' Often found in riverbeds or limestone outcrops. Collectors look for translucent varieties or those with unique colors (Jasper).
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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