sedimentary
Chert (Flint)
Chert (Microcrystalline Silica, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, white, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from ground fluids in limestone or chalk beds. Most common in Paleozoic and Mesozoic strata.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road construction, as a gemstone (Jasper/Agate varieties), and in landscaping.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital resources for prehistoric humans due to its ability to produce razor-sharp edges when fractured.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and waxy texture. It is frequently found as nodules or layers within limestone outcrops or as river-worn cobbles.
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Sandstone or Siltstone
Arenite (if sandstone)
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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
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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