sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, and gray with iron staining; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal.
- Hardness
- 7 Mohs
- Color
- Brown, tan, and gray with iron staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Brown, tan, and gray with iron staining; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal.
Formation & geological history
Formed primarily through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from groundwater within sedimentary beds like limestone.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; currently used for road surfacing and as a decorative stone in landscaping.
Geological facts
Because it breaks with a conchoidal fracture like glass, it was the primary material for prehistoric tool making. It is very chemically stable and resistant to weathering.
Field identification & locations
Identify by its hardness (it will scratch glass) and its smooth, shell-like fracture surfaces. Often found in nodules within limestone or as river gravel.
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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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