Flint

Mohs hardness of 7; color typically grey, white, brown, or black with a chalky outer cortex; waxy to vitreous luster; cryptocrystalline or microcrystalline structure; conchoidal fracture with no cleavage; specific gravity around 2.60 to 2.65.

Formed diagenetically as nodules or masses in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions, primarily during the Cretaceous period.

Historically used for making stone tools, arrowheads, and firearm ignition (flintlock mechanisms); occasionally used for decorative building stone, road aggregate, and grinding balls.

Flint and chert are essentially the same material, though 'flint' typically refers to the variety found in chalk deposits. Because of its extremely sharp conchoidal fracture edges, it was one of the most important materials for early human technological development during the Stone Age.

Easily identified by its characteristic smooth, conchoidal fracture, sharp edges, chalky outer rind, and high hardness capable of scratching glass and producing sparks when struck against steel. Found globally in chalk and limestone formations, particularly famous along the chalk cliffs of southern England and parts of Western Europe.