sedimentary
Chert (Polished/Worn)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-brown with white surface weathering; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-brown with white surface weathering
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-brown with white surface weathering; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in marine or groundwater environments. This specimen appears water-worn or tumbled.
Uses & applications
Historically used for stone tools/arrowheads. Currently used as road aggregate, in landscaping, and as a decorative rock for tumbling/polishing.
Geological facts
Chert is extremely durable and chemically stable. When it strikes steel, it can create sparks, which led to its use in flintlock firearms (specifically the variety known as flint).
Field identification & locations
Identify by its hardness (scratches glass), waxy feel, and smooth surfaces. Commonly found in limestone beds or as rounded pebbles in riverbeds and beaches.
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