Chert (Arrowhead/Tool Grade)

Physical Properties

Hardness: 7 on Mohs scale; Color: Mottled brown, grey, and black with translucent edges; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in limestone or chalk beds. Often Paleozoic or Mesozoic in age.

Uses & Applications

Historically used for stone tools and weapons due to sharp edges; currently used for decorative stone, flint-knapping enthusiasts, and occasionally in the construction of road bases.

Geological Facts

Chert exhibits conchoidal fracture, meaning it breaks like glass to produce razor-sharp edges. This piece shows signs of intentional flaking or 'knapping,' suggesting it may be a lithic debitage or tool fragment.

Field Identification & Locations

Identify in the field by its waxy texture, inability to be scratched by a steel blade, and sharp, shell-like fracture patterns. Commonly found in stream beds or eroding out of limestone outcrops.

Identified on: 4/19/2026

Mode: Standard