sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Cream, white, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Cream, white, gray, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, white, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from ground fluids in limestone or chalk beds. Most common in Paleozoic and Mesozoic strata.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as a gemstone (Jasper), and for historical artifacts.
Geological facts
Chert was one of the most important minerals for early humans due to its ability to fracture into sharp edges. It is chemically identical to quartz but has a different internal structure.
Field identification & locations
Identify by its waxy texture and distinctive shell-like (conchoidal) curved fractures. Often found as nodules within limestone or as river-worn pebbles. It will easily scratch glass.
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