Chert (Flint)

Hardness: 7 Mohs; Color: Gray, blue-gray, brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Often found as nodules in limestone or chalk beds. Geologically common in various eras.

Historically used for stone tools and weapons due to sharp fracture edges; currently used as road aggregate, in jewelry (as sea glass-like pendants), and for fire-starting.

Chert has a conchoidal fracture, similar to glass, which allows it to be knapped into extremely sharp blades. The provided coordinates in Southern Brazil (Rio Grande do Sul) are consistent with areas containing sedimentary basins where chert nodules occur within basaltic or sedimentary layers.

Identify by its smooth, waxy surface and its ability to scratch glass. Look for the characteristic shell-like (conchoidal) curves where the rock has broken. Found in river beds and sedimentary outcrops.