sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: White to tan with some staining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: White to tan with some staining
Luster: Waxy to dull

Identified June 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. This specimen appears to be a fragment, possibly a flake from tool-making.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregates, road surfacing, and as a component in early spark-striking fire starters.

Geological facts

This specimen displays classic conchoidal (shell-like) fracturing, which is the property that allowed ancient humans to knap it into sharp tools. It is often found as nodules inside limestone or chalk beds.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its smooth waxy surface, and characteristic curved fracture patterns. Common globally in sedimentary basins. Check for sharp edges that might indicate human modification (lithic debitage).