sedimentary
Chert (Serpentinized)
Silicon Dioxide (SiO2) with mineral staining
Hardness: 6.5-7 (Mohs), Color: Olive green to yellowish-brown, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Olive green to yellowish-brown, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich marine organisms or chemical precipitation. The greenish tint often results from hydrothermal alteration or proximity to serpentine/mafic rock complexes.
Uses & applications
Historically used for stone tools and weapons due to sharp fracture edges. Today used as an ornamental stone, for landscaping, or as a gemstone in tumbled jewelry.
Geological facts
Chert is so durable that it survives transport in riverbeds long after other rocks have eroded into sand. Green varieties are common in the Franciscan Complex of California.
Field identification & locations
Look for a waxy surface that feels smooth to the touch, conchoidal (shell-like) fracture patterns, and high hardness (it will scratch glass). Often found in riverbeds along coastal ranges.
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