sedimentary
Chert (Concretion or Nodular Variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Tan to yellow-brown, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan to yellow-brown, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica in sedimentary environments often replacing organic matter or precipitating within limestone/chalk beds; typically Paleozoic to Cenozoic in age.
Uses & applications
Historically used for making stone tools (flintknapping); currently used as a road aggregate, in landscaping, and as an indicator for geological mapping.
Geological facts
This specimen appears to be a weathered chert nodule or concretion; chert is so hard it can scratch glass and was once the primary material for prehistoric arrowheads.
Field identification & locations
Identify in the field by its conchoidal fracture (smooth, curved breaks) and extreme hardness. Commonly found in riverbeds or within limestone outcrops.
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