Flint (within Limestone matrix)

Physical Properties

Hardness: 7 (Mohs scale); Color: Black to dark grey interior with a tan/white chalky exterior; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed as nodules or masses in sedimentary rocks like chalk and limestone through the replacement of calcium carbonate by silica-rich fluids. Often dated to the Cretaceous period.

Uses & Applications

Historically used for stone tools and weapons (arrowheads/knives); used today as an abrasive, in road construction, and for manufacturing glass and ceramics. Also used as a fire starter.

Geological Facts

Flint was the primary material for the Stone Age tool industry. The sharp edges created by its conchoidal fracture can be thinner and sharper than a surgical steel scalpel.

Field Identification & Locations

Identify in the field by its smooth, glass-like interior revealed by cracks, and its distinctive curved (conchoidal) fracture pattern. It often produces sparks when struck against steel. Commonly found in chalk or limestone deposits.

Identified on: 4/23/2026

Mode: Standard