sedimentary

Chert (specifically Flint or Jasper variant)

Microcrystalline quartz (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Dark brown to black with reddish-brown edges. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (exhibits conchoidal fracture). Specific Gravity: 2.6–2.7.

Hardness: 6
Color: Dark brown to black with reddish-brown edges
Luster: Waxy to dull

Identified June 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 the chemical precipitation of silica in sedimentary basins. This specimen appears water-worn, suggesting a secondary transport history in a river or coastal environment.

Uses & applications

Historically used for making stone tools (knapping) due to its sharp edges. Currently used in construction aggregate, as a fire-starter (flint), and lower-quality pieces are used for landscaping or as aquarium stones.

Geological facts

Chert was one of the most vital materials for prehistoric humans; its ability to break into consistent, razor-sharp edges allowed for the creation of spears, arrowheads, and knives long before the Bronze Age.

Field identification & locations

Identify in the field by its smooth, waxy feel and the shell-like (conchoidal) curves where it has broken. Look for it in limestone or chalk deposits. It will easily scratch glass and strike sparks against steel.

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