sedimentary
Chert / Flint
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs); Color: Gray, blue-gray, brown, or tan; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7
- Hardness
- 7 (Mohs)
- Color
- Gray, blue-gray, brown, or tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs); Color: Gray, blue-gray, brown, or tan; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains such as radiolarians or diatoms, or by chemical precipitation in marine environments and limestone cavities. It occurs as nodules or layered beds within sedimentary rock strata (often Precambrian to Holocene).
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in construction aggregates, as a component in glassmaking, and frequently collected as river pebbles or landscape gravel.
Geological facts
Flint is a variety of chert that was essential to human survival for millennia because it produces sparks when struck against steel or iron pyrites, and it breaks into razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy surface and its distinct conchoidal (shell-like) fracture pattern. Found globally in creek beds, river gravels, and limestone outcrops. Collectors often look for unique colors or fossilized inclusions.
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