sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, white with banding; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, white with banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, white with banding; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.65
Formation & geological history
Forms primarily as nodules or layers in limestone or chalk through the accumulation of silica-rich organic remains like sponges or radiolarians, often during the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads); currently used in road construction, landscaping, and as a component in glass making.
Geological facts
The banding seen here represents episodic deposition of silica. Chert is so hard it can strike sparks against steel, making it a primary flint material.
Field identification & locations
Identify by its hardness (scratches glass), waxy feel, and sharp shell-like (conchoidal) edges when broken. Commonly found in stream beds or limestone outcrops.
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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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