sedimentary
Chert Nodule in Limestone
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brownish, or yellowish; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves)
- Hardness
- 7 (Mohs scale), Color: tan, brownish, or yellowish
- Color
- tan, brownish, or yellowish
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish, or yellowish; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves)
Formation & geological history
Formed through the accumulation of silica-rich fluids within carbonate sediment or by the replacement of calcium carbonate by silica during diagenesis in marine environments.
Uses & applications
Used historically for stone tools and fire-starting (flint); currently used in road construction, as an abrasive, and sometimes for decorative landscaping.
Geological facts
Chert is so hard it can scratch steel and was used by prehistoric humans to make arrowheads and scrapers because of its sharp conchoidal fracture edges.
Field identification & locations
Look for a hard, waxy-looking lump embedded in softer, grayish limestone or chalk; it will be noticeably more resistant to weathering than the surrounding rock.
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