Chert (Cherty Limestone or Flint)

Physical Properties

Hardness: 7 (Mohs scale), Color: Brown, tan, cream, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or sponge spicules) in marine or freshwater environments. This type of chert often occurs as nodules or lenses within carbonate rocks.

Uses & Applications

Historically used for stone tools due to its sharp edges; modernly used as road aggregate, in jewelry (as jasper), and as a decorative stone.

Geological Facts

Chert and flint were among the first materials used by early humans to create survival tools. When struck together with iron or pyrite, they create sparks, making them essential for primitive fire-starting. This specimen shows classic conchoidal (shell-like) fracturing common in high-silica rocks.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), smooth waxy texture, and sharp curved break patterns. Commonly found in limestone or chalk beds, riverbeds, and glacial deposits.

Identified on: 4/15/2026

Mode: Standard