Chert (variations include Flint or Jasper)

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: White, tan, or grey (in this specimen). Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.7.

Formation & Geological History

Formed from the precipitation of silica-rich fluids or the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) in marine environments. Often found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for stone tools (arrowheads/knives) due to its sharp edges. Today used in construction aggregate, road surfacing, and as a component in ceramics.

Geological Facts

Because of its conchoidal fracture pattern, chert breaks with extremely sharp edges, which is why it was the primary material for the 'Stone Age.' It is physically and chemically very resistant to weathering.

Field Identification & Locations

Identify in the field by its waxy texture, smooth curved (conchoidal) breaks, and its ability to scratch glass. It will not fizz with acid, distinguishing it from limestone. Commonly found in riverbeds or as nodules protruding from limestone cliffs.

Identified on: 4/27/2026

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