Chert

Chert is a hard, fine-grained sedimentary rock composed mainly of microcrystalline quartz (a form of silica). It often forms from the accumulation of tiny silica-rich shells or from silica-rich solutions that fill spaces in other sediments. Chert can appear in various colors, including gray, brown, green, or red, depending on impurities. It is commonly found as nodules or layers within other sedimentary rocks like limestone or shale. Due to its durability and sharp fracture, chert has historically been used to create tools and arrowheads.