sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or brownish-grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or brownish-grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or brownish-grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed primarily through the accumulation of silica-rich microfossils (like diatoms or radiolarians) or inorganic precipitation from silica-rich fluids within other sedimentary rocks like limestone.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Today used as road aggregate, architectural stone, and occasionally for lapidary work.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it creates very sharp edges. It is often found as nodules or layers within limestone beds.
Field identification & locations
Identify by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth concave breakage points. Common in sedimentary basins worldwide.
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