sedimentary
Chert (specifically Gray/Banded Chert)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, or smoky white with banding; Luster: Waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, or smoky white with banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, or smoky white with banding; Luster: Waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Used historically for stone tools and arrowheads; used industrially as a component in road construction, concrete aggregate, and occasionally as an abrasive or in decorative landscaping.
Geological facts
Chert was one of the first materials used by early humans to create sharp tools because of its conchoidal fracture, which produces razor-sharp edges. It is chemically identical to jasper and flint but generally lighter in color and more opaque.
Field identification & locations
Identify in the field by its hardness (it scratches glass), waxy feel, and curved 'clamshell' fracture patterns. Commonly found in limestone and dolomite formations as nodules or layered beds globally.
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