sedimentary
Chert (Jasper-rich)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan, yellow, and reddish-brown (iron-stained), 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 scale), Color: tan, yellow, and reddish-brown (iron-stained), Luster: dull to waxy, Crystal structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (diatoms, radiolarians) or chemical precipitation from fluids within sedimentary layers. This specific specimen shows iron oxide staining characteristic of weathered outcrops.
Uses & applications
Historically used for stone tools and arrowheads; currently used in jewelry (as jasper), landscaping, and as a component in construction aggregates.
Geological facts
Chert is so durable it can survive millions of years of transport in rivers. When struck against steel, it can create sparks, which led to its use in flintlock firearms.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), conchoidal (shell-like) fracture patterns, and lack of visible grains. Commonly found in limestone or chalk beds and river gravels.
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