sedimentary
Chert (often called Jasper or River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: dark brown, reddish-brown, and black; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65
- Hardness
- 6
- Color
- dark brown, reddish-brown, and black
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: dark brown, reddish-brown, and black; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen appears water-worn and smoothed by alluvial processes.
Uses & applications
Historical use for stone tools (flintknapping), modern use as decorative landscape stone, gravel, and occasionally tumbled for jewelry or pocket stones.
Geological facts
Chert is one of the most durable sedimentary rocks. It was the primary material used by prehistoric humans to create sharp-edged tools like arrowheads and knives due to its predictable breaking pattern.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), smooth waxy texture, and curved, shell-like (conchoidal) fracture lines. Found globally in riverbeds, glacial tills, and sedimentary outcrops.
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