sedimentary
Chert
Microcrystalline Quartz (SiO2)
Mohs Hardness: 7, Color: Cream to tan with grayish patches, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7
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Physical properties
Mohs Hardness: 7, Color: Cream to tan with grayish patches, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids or the accumulation of silica-based micro-organisms in marine environments. It typically occurs as nodules or layers within limestone or dolostone formations.
Uses & applications
Historically used for stone tools and arrowheads; used industrially as a road base material, in concrete aggregate, and occasionally in lapidary work for cabochons.
Geological facts
Chert is so hard it can strike sparks from steel, a property used by ancient peoples for fire-starting. It is often synonymous with flint, although flint is technically a dark-colored variety found in chalk.
Field identification & locations
Identifiable by its extreme hardness (scratches glass), smooth conchoidal fracture edges, and dense, non-porous texture. Commonly found in creek beds and limestone outcrops.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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