sedimentary
Chert (Jasper/Pink Chert)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs), Color: Pink, white, and tan, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Pink, white, and tan, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms or through the chemical precipitation of silica in sedimentary environments like marine basins. This specific banding suggests a secondary replacement or a vein-filling process.
Uses & applications
Used historically for arrowheads and scrapers due to its sharp conchoidal fracture. Modern uses include decorative lapidary arts, jewelry (as jasper), and gravel for construction.
Geological facts
Chert was one of the first materials used by early humans to create tools. The pink coloration is typically caused by trace amounts of iron oxide (hematite) within the silica matrix.
Field identification & locations
Identify in the field by its hardness (it can scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial till, and within limestone or dolostone formations.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
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