sedimentary
Chert (Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: brown, grey, tan; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8
- Hardness
- 7 (Mohs scale)
- Color
- brown, grey, tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: brown, grey, tan; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8
Formation & geological history
Formed in sedimentary environments as nodules or bedding layers through the precipitation of silica-rich fluids. Commonly occurs in limestone and chalk formations.
Uses & applications
Used historically for stone tools and fire-starting; currently used as aggregate in road construction and as decorative garden stones.
Geological facts
Because it fractures with sharp edges, chert was one of the most important materials for early humans to create arrowheads, knives, and scrapers.
Field identification & locations
Identify by its extreme hardness (scratches glass) and conchoidal (shell-like) fracture patterns. Often found in riverbeds or eroded out of limestone cliffs.
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