sedimentary

Chert (Brown variety)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan to chocolate brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz fibers); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan to chocolate brown
Luster: Waxy to dull

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from hydrothermal fluids. This specimen likely originates from nodules within limestone or shale beds, often dating to the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads and scrapers) due to its sharp edges. Modern use includes road surfacing, grinding media in ball mills, and occasionally as an ornamental stone in jewelry (lapidary).

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, making it a primitive tool for fire-making. It is structurally nearly identical to flint, though 'flint' is a term usually reserved for chert found in chalk deposits.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its inability to be scratched by a knife. Common in areas with limestone or dolomite outcrops, often appearing as distinct 'lumps' or nodules within the softer host rock.