sedimentary
Chert (Chert Nodule)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, grey, creamy white, often weathered surface; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, grey, creamy white, often weathered surface
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, grey, creamy white, often weathered surface; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic debris (like sponges or radiolaria) or chemical precipitation in marine environments. These nodules typically form within limestone or chalk beds. Most specimens can range from hundreds of millions of years old to relatively recent geological eras.
Uses & applications
Used historically for stone tools and weapons due to its sharp edges when fractured. Modern uses include abrasives, road construction material, and occasionally as a decorative landscape stone.
Geological facts
Because of its high hardness and brittle nature, prehistoric humans used this material to create 'flint' tools. 'Flint' is technically a variety of dark chert found in chalk or marly limestone.
Field identification & locations
Identify in the field by its rounded, nodular shape, smooth waxy texture on fresh surfaces, and ability to scratch glass. It will not react with acid (unlike the limestone it is often found in) and exhibits shell-like (conchoidal) fractures when broken.
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