sedimentary
Chert Pebble with Inclusion
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Cream, tan, and grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream, tan, and grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, followed by physical weathering and smoothing in a river or coastal setting. Likely Cretaceous to Cenozoic era.
Uses & applications
Used historically for stone tools; currently used as construction aggregate, in landscaping, or for decorative pebble collecting.
Geological facts
Chert is so hard it can create sparks when struck against steel. This specimen shows a distinct band or 'inclusion' which may be a trace fossil or a variation in mineral concentration during formation.
Field identification & locations
Identify by its hardness (scratches glass), waxy feel, and smooth surface from water erosion. Found globally in riverbeds, beaches, and glacial till.
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