sedimentary
Chert (Yellow/Tan)
Microcrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Pale yellow to tan with translucent edges. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Pale yellow to tan with translucent edges
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Pale yellow to tan with translucent edges. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms. Often found as nodules within limestone or shale beds.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used as road aggregate, architectural stone, and for decorative lapidary work.
Geological facts
Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was one of the most high-value materials for prehistoric humans to craft sharp-edged tools and weapons.
Field identification & locations
Identify in the field by its hardness (will scratch steel and glass), waxy luster, and smooth, shell-like chips on the corners. Found globally in sedimentary basins.
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