As you may have seen, throughout the topic we have talked about the materials of the earth's crust and we have not used the word stone even once. We will never use this term in geology. We will use the term mineral and rock instead.
Most rocks are formed by the association of several different minerals. For example, granite is made up of several components, which are different minerals. The gray (or transparent) mineral is quartz, the black mineral is called mica, and the white is called feldspar.
However, some rocks are made up of only one type of mineral. Thus, limestone rock is made up solely of the mineral calcite.
Taking all this into account, a rock can be defined as the association of one or several minerals.