Flint is a sedimentary rock composed entirely of silica. It occurs as concretions, in band or nodule form, in limestones, especially chalk. ItAElig;s colour is usually black, brown or tan. It is marine in origin. Flint is a hard, tough stone which fractures conchoidally. Flakes of Flint were used by primitive people for making arrowheads, scrapers, and other tools.