sedimentary
Chert (Field Stone)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: tan, light brown, white; Luster: waxy to dull; Structure: microcrystalline; Fracture: conchoidal; Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, light brown, white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, light brown, white; Luster: waxy to dull; Structure: microcrystalline; Fracture: conchoidal; Gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of marine organisms or through chemical precipitation in groundwater replacing limestone or dolostone
Uses & applications
Traditionally used for tool making (arrowheads); currently used as road aggregate, railroad ballast, or for landscaping
Geological facts
Because of its high hardness and conchoidal fracture, chert was one of the most important materials for early human technology (Stone Age tools)
Field identification & locations
Identify by its ability to scratch glass and its smooth, shell-like fracture surfaces; commonly found as nodules in limestone beds or as stream pebbles
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