sedimentary
Chert (with Lichen)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Highly variable (tan, grey, red, brown). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6.
- Hardness
- 6
- Color
- Highly variable (tan, grey, red, brown)
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Highly variable (tan, grey, red, brown). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in marine environments. It can be found in strata ranging from Precambrian to Cenozoic ages.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road surfacing, decorative landscaping, and occasionally as a gemstone when colorful (Jasper).
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, ideal for cutting tools and weapons. The specimen in the image is host to crustose and foliose lichens.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster on fresh breaks, and smooth, shell-like (conchoidal) fracture surfaces. Common in limestone and dolomite formations worldwide.
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