sedimentary
Chert (with Liesegang Banding)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, orange, and grey bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Tan, orange, and grey bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, orange, and grey bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. The colored rings are Liesegang bands, formed by chemical precipitation of iron oxides within a porous rock during weathering or diagenesis.
Uses & applications
Historical use for tool-making (arrowheads/knives) due to conchoidal fracture; modern uses include landscaping, construction aggregate, and as collectible specimens for geologists.
Geological facts
The rhythmic ring patterns, known as Liesegang bands, are a fascinating example of periodic chemical precipitation, similar to the process that forms rings in agate or Tiger's Eye.
Field identification & locations
Identify in the field by its hardness (will scratch glass), conchoidal fracture patterns, and its distinct chemical bands that follow the shape of the rock's outer surface.
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