CHERT: A coarse type of siliceous (silica) rock, a form of quartz, used for the manufacture of stone tools where flint was not available. It is of poorer quality than flint, formed from ancient ocean sediments, and often has a semi-glassy finish. It is pinkish, white, brown, gray, or bluegray in color. Flint, chert, and other siliceous rocks like obsidian are very hard, and produce a razor-sharp edge when properly flaked into tools. This crystalline form of the mineral silica is found as nodules in limestones. Varieties of chert are jasper, chalcedony, agate, flint, and novaculite. Chert and flint provided the main source of tools and weapons for Stone Age man.