Rocks consisting of micro-crystalline or sub micro-crystalline accumulations of silica have been sought by man since earliest times, as their fine grain size, homogeneity, hardness, and conchoidal fracture make them ideal for the production of cutting edges for tools and weapons. The widespread distribution and extensive use of these rocks has resulted in them being given a multiplicity of names, some of great antiquity. Textural and colour variations can justify some of these names. However, it is convenient to have a term which covers all rocks of this type, and in modern geological literature chert is the term which is becoming increasingly accepted.