sedimentary
Chert (with small quartz vug)
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: Cream, tan, and white, Luster: Waxy to dull, Crystal Structure: Microcrystalline with small macrocrystalline quartz crystals in the cavity, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream, tan, and white, Luster: Waxy to dull, Crystal Structure: Microcrystalline with small macrocrystalline quartz crystals in the cavity, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from silica-rich groundwater within limestone or chalk beds. Often Cretaceous or Paleogene in age.
Uses & applications
Historically used for making stone tools (flint); currently used for road surfacing, as an abrasive, and by crystal collectors for specimens with unique vugs.
Geological facts
Chert is so hard it can scratch steel and glass. It is often found as nodules or layers within sedimentary rocks like limestone. The small hole in this specimen is called a 'vug,' which allows for larger crystal growth.
Field identification & locations
Identify in the field by its hardness (it cannot be scratched by a knife) and its smooth, shell-like (conchoidal) fracture pattern. Found globally in sedimentary basins.
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