sedimentary
Chert (often called Flint or River Stone)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, and brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (has conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, and brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (has conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or freshwater environments. This specimen appears water-worn, likely from a river or glacial deposit.
Uses & applications
Historically used for stone tools (arrowheads); currently used in road construction as aggregate, in landscaping, and as a durable lapidary material for tumbling.
Geological facts
Chert is so hard that it can scratch steel. When struck against steel, it can create sparks, which is why darker varieties (flint) were used in flintlock firearms.
Field identification & locations
Identify by its waxy texture, extreme hardness, and 'shell-like' curved breaks (conchoidal fracture). It is extremely common in riverbeds and gravel pits worldwide.
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