The hardness of a mineral is a mechanical property that refers to its resistance to being scratched, carved, or ground by other objects. When the mechanical energy of an external object is used to carve or press into a mineral, the mineral itself shows a certain degree of firmness, and this degree of firmness is the measure of its hardness, expressed as H. Based on the previous research (Wang et al. 1982; Pan 1993) and the research work of the author of this book, the mechanical properties related to the mechanical function of mineral materials, one of which is the hardness of minerals, will be introduced here.