sedimentary
Chert (often called Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown with a waxy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or layers in limestone through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. Found in sedimentary basins worldwide.
Uses & applications
Historically used for stone tools and making fire (striking steel). Modernly used as a road base, in construction aggregate, and occasionally as a semi-precious gemstone.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture produces extremely sharp edges, ideal for spearheads and knives.
Field identification & locations
Identify in the field by its waxy appearance and shell-like (conchoidal) breakage patterns. It will easily scratch glass. Commonly found in limestone outcrops or as rounded pebbles in stream beds.
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