sedimentary
Chert (variously known as Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Black, grey, translucent white; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Black, grey, translucent white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Black, grey, translucent white; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic debris (like sponge spicules or radiolarians) or the chemical replacement of limestone/chalk by silica in marine environments.
Uses & applications
Historically used for stone tools and starting fires (flint); currently used in jewelry (as jasper/agate variants) and as a decorative stone or abrasive.
Geological facts
Chert was the primary material for prehistoric arrowhead and scrapers due to its predictable conchoidal fracture which creates razor-sharp edges.
Field identification & locations
Identify by its 'shell-like' curved fractures and ability to scratch glass. Commonly found as nodules in limestone beds or as pebbles in stream beds.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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