sedimentary
Chert / River Pebble
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: dark brown, grey, or tan; Luster: waxy to dull; Crystal structure: trigonal (microscopic); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- dark brown, grey, or tan
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: dark brown, grey, or tan; Luster: waxy to dull; Crystal structure: trigonal (microscopic); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or lacustrine environments. This specimen has been rounded and smoothed through water erosion in a river or glacial setting.
Uses & applications
Historically used for stone tools (arrowheads); currently used in road construction, landscaping, and as decorative river stones.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early human civilizations due to its conchoidal fracture which creates sharp edges.
Field identification & locations
Identify by its extreme hardness, waxy texture when broken, and lack of visible grains. Common in sedimentary basins and riverbeds worldwide.
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