sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: typically gray, tan, or brown; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8
- Hardness
- 6
- Color
- typically gray, tan, or brown
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: typically gray, tan, or brown; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8
Formation & geological history
Formed through the precipitation of silica in sedimentary environments, often replacing organic matter or limestone. This specimen shows a water-worn, rounded shape indicating transportation in a river or coastal environment.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracture. Currently used in road construction, as decorative gravel, and occasionally for lapidary work.
Geological facts
Chert is a high-silica rock that often contains micro-fossils. Flint is the most famous variety of chert, known for its ability to create sparks when struck against steel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel) and its smooth, waxy feel when freshly broken. Found globally in limestone formations and as pebbles in riverbeds.
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