sedimentary
Chert Pebble with Quartz Veining
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brownish-tan with white crystalline veins; Luster: Waxy to dull (earthy); Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Brownish-tan with white crystalline veins
- Luster
- Waxy to dull (earthy)
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-tan with white crystalline veins; Luster: Waxy to dull (earthy); Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. The white vein indicates a secondary fracture filling by hydrothermal quartz fluids. Usually dated from the Paleozoic to Mesozoic eras.
Uses & applications
Historically used for stone tools (flintknapping); currently used in decorative landscaping, river rock drainage, and as a durable abrasive in grit blasting.
Geological facts
Chert is so durable that it often survives as smooth pebbles in riverbeds long after the surrounding limestone bedrock has eroded away. It is often referred to as 'flint' when found in chalk or dark gray colors.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel) and its characteristic conchoidal fracture (smooth, curved breaks). Look for it in stream beds and gravel pits.
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