sedimentary
Chert Nodule
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Brown rind with grey-tan interior, Luster: Dull to waxy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 Mohs, Color: Brown rind with grey-tan interior, Luster: Dull to waxy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in sedimentary rocks through the precipitation of silica from groundwater, often replacing organic matter or filling voids. Usually found in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used for landscaping, aggregate, and as a collector's specimen.
Geological facts
Chert and its variety flint were essential to early human technology because they break with extremely sharp edges. Many nodules form in deep sea environments.
Field identification & locations
Identify by its smooth, waxy interior surface when broken and its characteristic conchoidal (shell-like) fracture patterns. Look for a chalky or weathered outer 'rind'.
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