sedimentary
Chert (Beach Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan/Grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan/Grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan/Grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools/arrowheads; currently used as construction aggregate, road surfacing, and decorative pocket stones.
Geological facts
Chert is so hard it can strike sparks against steel. It is a common constituent of 'sea glass' mimics when tumbled by ocean waves.
Field identification & locations
Identify in the field by its hardness (it scratches glass) and smooth, rounded water-worn texture. Found globally on beaches and in stream beds. Collectors look for unique colors or banding.
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