sedimentary

Chert (often called Flint or Jasper)

Cryptocrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, or gray
Luster: Waxy to dull

Identified April 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) on the ocean floor, or through chemical precipitation in groundwater. It can found in nodules within limestone or as bedded deposits.

Uses & applications

Historically used for stone tools and starting fires; currently used as a gemstone (when colorful like jasper), in road construction, and as a component in glass making.

Geological facts

Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's steel scalpel, making it the primary material for prehistoric arrowheads and spear tips.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fracture marks. Look for it in limestone or chalk outcrops.