sedimentary

Chert (specifically Red Chert / Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale; Color: Reddish-brown, tan, and gray waxy tones; Luster: Greasy to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on the Mohs scale
Color: Reddish-brown, tan, and gray waxy tones
Luster: Greasy to waxy

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most specimens date back to the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools and arrowheads; currently used as construction aggregate, road surfacing, and in some decorative lapidary jewelry like cabochons.

Geological facts

Because of its conchoidal fracture, it breaks with extremely sharp edges. It was the primary material for 'flintknapping' by prehistoric humans. It can also produce sparks when struck against steel, making it vital for fire-starting.

Field identification & locations

Identify in the field by its smooth, shell-like fracture pattern and inability to be scratched by a steel knife. It is frequently found in stream beds or within limestone outcrops globally, especially in the Midwestern United States and the UK.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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