sedimentary
Chert (varieties include Flint and Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan (as seen in the specimen); Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none, exhibits distinct conchoidal fracture; Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically grey, brown, or tan (as seen in the specimen)
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan (as seen in the specimen); Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none, exhibits distinct conchoidal fracture; Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich biogenic remains (like diatoms or radiolaria) or chemical precipitation in marine environments and limestone cavities. It can range from precambrian to recent geological ages.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges; modern uses include road surfacing, jewelry (as jasper/agate), and as a strike-stone for fire-starting.
Geological facts
Chert was one of the most important minerals to prehistoric humans; its ability to break into razor-sharp edges made it essential for survival. It is so tough it can spark when struck against steel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, curved 'shell-like' (conchoidal) fracture surfaces. Commonly found as nodules or layers within limestone or chalk formations.
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