sedimentary
Chert
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: tan, brown, or gray, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brown, or gray, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Forms through the precipitation of silica from seawater or the accumulation of silica-rich organic remains like sponges and radiolarians. Often found as nodules in limestone or as bedded deposits.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include road surfacing materials, decorative landscaping, and as a raw material for silicon production.
Geological facts
Because it breaks with a conchoidal fracture like glass, it produces very sharp edges, which is why it was the primary material for prehistoric weapons and cutting tools.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its waxy luster on fresh broken surfaces. Found globally in sedimentary basins.
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