sedimentary
Chert (Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most specimens date from the Phanerozoic eon.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used in road construction, as architectural veneer, and in jewelry as 'Jasper' when brightly colored.
Geological facts
Chert is so hard it can create sparks when struck against steel, a property used for centuries to start fires. It is also the primary material for the world's oldest known manufactured tools.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and sharp edges. It will easily scratch glass. Commonly found as nodules or layers within sedimentary limestone outcrops globally.
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