sedimentary
Chert Pebble (with fossil shell fragment)
Microcrystalline Quartz (SiO2) with Calcified Invertebrate Impression
Hardness: 7.0 (Mohs scale); Color: Cream, tan, and brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7
- Color
- Cream, tan, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7.0 (Mohs scale); Color: Cream, tan, and brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed during the diagenesis of marine sediments where silica-rich fluids replace calcium carbonate or organic matter. This specimen appears to contain a fossilized mold/impression of a bivalve or brachiopod shell, likely from the Paleozoic or Mesozoic era.
Uses & applications
Informational/educational specimen, decorative gravel, or used historically for stone tools due to its sharp-edged fracture properties.
Geological facts
Chert is so durable that it often remains as rounded river pebbles long after the surrounding limestone bedrock has eroded away. The visible patterns are 'steinkerns' or internal molds of ancient marine life.
Field identification & locations
Identify by its hardness (it will scratch glass) and waxy texture. Commonly found in riverbeds, glacial tills, and coastal beaches. Look for the distinct 'u-shaped' fossil impressions on the surface.
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