sedimentary
Banded Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Gray, white, and brown banding; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Gray, white, and brown banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Gray, white, and brown banding; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments, subsequently smoothed by water erosion in a river or coastal setting.
Uses & applications
Primarily used in landscaping, as a decorative garden stone, or for lapidary tumbling. Historically used for stone tools due to its sharp fracture edges.
Geological facts
Chert is one of the most durable sedimentary rocks and can preserve microfossils. Banded varieties are often called 'ribbon chert' when found in massive geological formations.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, rounded texture compared to surrounding rocks. Often found in riverbeds or on beaches.
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