sedimentary
Chert (or Cryptocrystalline Quartz)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Brown/Tan with white inclusions, Luster: Waxy to dull, Crystal structure: Microcrystalline/trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/Tan with white inclusions, Luster: Waxy to dull, Crystal structure: Microcrystalline/trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed primarily by the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or through the chemical precipitation of silica in groundwater. This specimen appears water-worn or tumbled.
Uses & applications
Used historically for stone tools (arrowheads), as striking stones for fire-starting, and currently as construction aggregate or decorative garden stone.
Geological facts
Chert is essentially the same material as flint, but the term 'flint' is usually reserved for dark varieties found in chalk or limestone. It is one of the most durable sedimentary rocks.
Field identification & locations
Identify in the field by its waxy luster, smooth surface (if water-worn), and its ability to scratch glass. It is commonly found in riverbeds, glacial deposits, and as nodules within limestone sequences.
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