sedimentary
Chert (Green variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Olive green to grey-green; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Olive green to grey-green
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Olive green to grey-green; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or chemical precipitation from silica-rich fluids in marine environments. Often found as nodules or layered beds in limestone or shale.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; used today as a decorative stone, in jewelry (as jasper/agate), and occasionally in industrial grinding media.
Geological facts
Chert is so hard it can create sparks when struck against steel. The green color is often due to the presence of chlorite or other mineral inclusions. It was one of the most important raw materials for prehistoric humans.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and high hardness (will scratch glass). Common in sedimentary basins worldwide. Tip: look for smooth, waxy surfaces on broken faces.
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