sedimentary
Chert (Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, or gray
- Luster
- Waxy to dull
Identified More sedimentary →
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or by chemical precipitation in limestone or chalk beds. Commonly found in Paleozoic to Mesozoic sedimentary layers.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a semi-precious stone in jewelry making.
Geological facts
Chert was one of the most important minerals for early humans because of its ability to break into extremely sharp edges. This specific specimen shows distinct conchoidal fracturing ripples.
Field identification & locations
Identify in the field by its smooth, waxy surface and characteristic curved (conchoidal) breaks. It can scratch glass and will not react with acid like the limestone it often sits in.
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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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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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