sedimentary
Chert (River Pebble)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7. It is dense and hard.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or buff
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7. It is dense and hard.
Formation & geological history
Formed as a chemical precipitate or biochemical deposit in sedimentary environments, often starting as a silica-rich gel on the ocean floor. This specific specimen has been rounded and smoothed by water transport in a river or coastal environment.
Uses & applications
Historically used for stone tools (arrowheads) due to sharp fracture edges. Today, primarily used in construction aggregate, road base, and as decorative landscaping stones.
Geological facts
Chert is essentially a type of flint. It is so hard that it can scratch glass and steel. It often forms as nodules within limestone or chalk beds.
Field identification & locations
Identify by its smooth, waxy feel, extreme hardness, and conchoidal (shell-like) fractures where chipped. Commonly found in riverbeds, gravel pits, and coastal beaches.
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