sedimentary
Flint (chert) with chalcedony/quartz
Microcrystalline quartz, SiO₂; likely flint or siliceous chert with a chalcedonic edge
AI-generated identification · may be incorrectHardness about 7 Mohs; dark gray to black, waxy-to-dull luster, cryptocrystalline quartz, conchoidal fracture, and no visible cleavage. The pale translucent margin is probably chalcedony or weathered silica.
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Physical properties
Hardness about 7 Mohs; dark gray to black, waxy-to-dull luster, cryptocrystalline quartz, conchoidal fracture, and no visible cleavage. The pale translucent margin is probably chalcedony or weathered silica.
Formation & geological history
Forms when silica replaces carbonate sediment or accumulates from biogenic silica, later hardening during diagenesis; commonly Cretaceous to Paleozoic, though the specimen’s age cannot be determined visually.
Uses & applications
Used historically for sharp tools and fire-starting, and today for knapping, decorative stone, lapidary work, and limited aggregate applications.
Geological facts
Its sharp conchoidal edges are characteristic of flint and can produce sparks against steel; the dark color commonly reflects organic matter or finely dispersed impurities.
Field identification & locations
Identify by its very hard, fine-grained texture, waxy appearance, and curved shell-like fracture; it commonly occurs as nodules or layers in limestone and chalk. The image may also show a worked or naturally fractured edge.
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