sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brownish-olive to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Brownish-olive to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-olive to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from water, followed by burial and lithification. This specimen has been rounded and smoothed by water erosion in a river or beach environment.
Uses & applications
Historically used for making stone tools (flintknapping). Today used in landscaping, as aggregate in construction, and occasionally for lapidary work or as talismans.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for hunting and scraping tools. It is also known as flint in scientific contexts when found in chalk or marly limestone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth appearance when rounded. Found globally in riverbeds and sedimentary basins.
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