sedimentary
Chert (Flint) with Limestone Matrix
Silicon Dioxide (SiO2) within Calcium Carbonate (CaCO3)
Hardness: 7 (Chert) / 3 (Limestone), Color: Tan, brown, white, and translucent gray, Luster: Waxy to vitreous (Chert) and dull (Limestone), Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Chert) / 3 (Limestone), Color: Tan, brown, white, and translucent gray, Luster: Waxy to vitreous (Chert) and dull (Limestone), Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through chemical precipitation of silica in marine environments, often replacing organic matter or filling voids in limestone seafloors. This specimen shows a nodule or fragment of chert embedded in its original host limestone.
Uses & applications
Historically used for stone tools and fire-starting (flint); currently used as an abrasive, in road construction, and for geological collecting.
Geological facts
This specimen shows the transition between the sedimentary host rock and the silica nodule. Flint is a variety of chert that occurs specifically in chalk or marly limestone deposits.
Field identification & locations
Identify in the field by the conchoidal (shell-like) fracture patterns on the shiny edges and the sharp difference in hardness between the white crust and the glassy interior. Common in sedimentary basins worldwide.
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