sedimentary
Chert (Silica Pebble)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, and gray; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, and gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, and gray; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich marine organisms or chemical precipitation of silica in groundwater. Often found as nodules within limestone or as stream-worn pebbles.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include construction aggregate, architectural stone, and as a durable material for stone tumbling.
Geological facts
Chert is so durable that it often survives as a smooth pebble long after the surrounding limestone bedrock has eroded away. It is chemically identical to flint but usually lighter in color.
Field identification & locations
Identify in the field by its hardness (will scratch glass), conchoidal (shell-like) fracture, and smooth, waxy texture. Commonly found in riverbeds, gravel pits, and coastal areas.
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