sedimentary
Chert (Chert / Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-tan (liver color), Luster: Waxy to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (characterized by conchoidal fracture), Specific Gravity: 2.6 - 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan (liver color), Luster: Waxy to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (characterized by conchoidal fracture), Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids. Often found as nodules or layers in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used as flint for fire-starting; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert and flint were among the first materials used by early humans to create tools; the conchoidal fracture allows it to break into edges that can be sharper than a surgical steel scalpel.
Field identification & locations
Identify by its 'glassy' conchoidal fracture (curved, shell-like breaks) and that it cannot be scratched by a steel knife but can scratch glass. Often found in gravel pits or weathered out of limestone outcrops.
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