sedimentary
Chert (Hag Stone / Hole Stone)
Chert (Cryptocrystalline variety of Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-red to tan (iron staining), Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-red to tan (iron staining), Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. The holes are typically formed via 'boring' by marine organisms like piddock clams or long-term water erosion within high-energy tidal zones.
Uses & applications
Historically used for making stone tools due to its hardness and sharp edges. Today used as an abrasive, in landscaping, and as 'Hag Stones' for spiritual or decorative collecting.
Geological facts
Specimens with naturally occurring holes are known as 'Hag Stones' or 'Odin Stones.' In folklore, they were believed to protect the wearer from the evil eye, nightmares, and witchcraft.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, hole-ridden texture. Commonly found on beaches or in riverbeds where water action is constant. Collectors look for unique hole placements and natural weathering patterns.
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