sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brownish-tan with a pinkish band; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-tan with a pinkish band
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-tan with a pinkish band; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestone or through the accumulation of siliceous organic remains (like diatoms or radiolarians). Formation can range from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to its sharp edges when fractured. Modern uses include road surfacing, jewelry (when colorful), and fire-starting tools (flint and steel).
Geological facts
Chert is so durable that it often survives much longer than the host rocks it formed in, which is why it is frequently found as pebbles in stream beds. The pink banding in this specimen is likely due to trace impurities of iron oxide (hematite).
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy feel, and smooth, shell-like (conchoidal) fracture patterns. It is common worldwide in limestone-heavy regions.
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