sedimentary
Chert (Smooth River Pebble)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline (grains too small to see with a microscope); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline (grains too small to see with a microscope); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen is a water-worn, smoothed pebble likely shaped over thousands of years in a riverbed.
Uses & applications
Historically used for making stone tools (flintknapping). Today used as decorative gravel, in landscaping, as a gemstone (jaspers), and as an abrasive.
Geological facts
Chert is so hard it can create sparks when struck against steel. It is chemically identical to quartz but has a different internal structure. Ancient people valued it for its predictable, razor-sharp fracture edges.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, rounded shape if found near water. Common in limestone deposits and riverbeds worldwide.
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