sedimentary
Banded Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, green-gray, with dark bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, green-gray, with dark bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, green-gray, with dark bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age can range from Precambrian to Cenozoic.
Uses & applications
Used historically for stone tools and arrowheads; currently used in jewelry (lapidary), as a gemstone, or in construction aggregate and road surfacing.
Geological facts
Banded chert often contains the iron-rich variety known as jasper. Some of the oldest fossils on Earth, found in the Gunflint Chert, are preserved within these types of siliceous rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fracture; commonly found in riverbeds or as nodules within limestone.
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