sedimentary
Chert (often called Flint or Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Brown/Opaque, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6 – 2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/Opaque, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6 – 2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation out of groundwater in limestone or dolomite formations.
Uses & applications
Historically used for stone tools (arrowheads). Used today as an industrial abrasive, in road construction, and occasionally in jewelry as Jasper.
Geological facts
Because of its conchoidal fracture, it breaks into sharp edges, making it the primary material for the 'Stone Age'. It can produce sparks when struck against steel.
Field identification & locations
Identify in the field by its smooth, waxy surface and the concave 'shell-like' curves (conchoidal fractures) where it has been broken. It is a very hard rock that can scratch glass.
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