sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Dark grey, brownish-red to black; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.65.

Hardness: 7 on Mohs scale
Color: Dark grey, brownish-red to black
Luster: Waxy to vitreous

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids. This specimen shows typical layering and a smooth, glass-like fracture common in sedimentary basins ranging from Precambrian to Cenozoic ages.

Uses & applications

Used historically for stone tools and weapons due to its sharp edges; modernly used in road construction, as a source for silica, and for lapidary work/jewelry.

Geological facts

Because of its high hardness and glass-like fracture, it was one of the most important minerals for early humans to create arrowheads and scrapers. It can create sparks when struck against steel.

Field identification & locations

Identify in the field by its distinct shell-like (conchoidal) fracture patterns, waxy texture, and inability to be scratched by a steel knife. Common in limestone and chalk formations globally.

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